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f41d911f PM |
1 | /* |
2 | * Read-Copy Update mechanism for mutual exclusion (tree-based version) | |
3 | * Internal non-public definitions that provide either classic | |
6cc68793 | 4 | * or preemptible semantics. |
f41d911f PM |
5 | * |
6 | * This program is free software; you can redistribute it and/or modify | |
7 | * it under the terms of the GNU General Public License as published by | |
8 | * the Free Software Foundation; either version 2 of the License, or | |
9 | * (at your option) any later version. | |
10 | * | |
11 | * This program is distributed in the hope that it will be useful, | |
12 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
14 | * GNU General Public License for more details. | |
15 | * | |
16 | * You should have received a copy of the GNU General Public License | |
87de1cfd PM |
17 | * along with this program; if not, you can access it online at |
18 | * http://www.gnu.org/licenses/gpl-2.0.html. | |
f41d911f PM |
19 | * |
20 | * Copyright Red Hat, 2009 | |
21 | * Copyright IBM Corporation, 2009 | |
22 | * | |
23 | * Author: Ingo Molnar <mingo@elte.hu> | |
24 | * Paul E. McKenney <paulmck@linux.vnet.ibm.com> | |
25 | */ | |
26 | ||
d9a3da06 | 27 | #include <linux/delay.h> |
3fbfbf7a | 28 | #include <linux/gfp.h> |
b626c1b6 | 29 | #include <linux/oom.h> |
62ab7072 | 30 | #include <linux/smpboot.h> |
4102adab | 31 | #include "../time/tick-internal.h" |
f41d911f | 32 | |
5b61b0ba MG |
33 | #define RCU_KTHREAD_PRIO 1 |
34 | ||
35 | #ifdef CONFIG_RCU_BOOST | |
36 | #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO | |
37 | #else | |
38 | #define RCU_BOOST_PRIO RCU_KTHREAD_PRIO | |
39 | #endif | |
40 | ||
3fbfbf7a PM |
41 | #ifdef CONFIG_RCU_NOCB_CPU |
42 | static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */ | |
43 | static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */ | |
1b0048a4 | 44 | static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */ |
3fbfbf7a PM |
45 | static char __initdata nocb_buf[NR_CPUS * 5]; |
46 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ | |
47 | ||
26845c28 PM |
48 | /* |
49 | * Check the RCU kernel configuration parameters and print informative | |
50 | * messages about anything out of the ordinary. If you like #ifdef, you | |
51 | * will love this function. | |
52 | */ | |
53 | static void __init rcu_bootup_announce_oddness(void) | |
54 | { | |
55 | #ifdef CONFIG_RCU_TRACE | |
efc151c3 | 56 | pr_info("\tRCU debugfs-based tracing is enabled.\n"); |
26845c28 PM |
57 | #endif |
58 | #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32) | |
efc151c3 | 59 | pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n", |
26845c28 PM |
60 | CONFIG_RCU_FANOUT); |
61 | #endif | |
62 | #ifdef CONFIG_RCU_FANOUT_EXACT | |
efc151c3 | 63 | pr_info("\tHierarchical RCU autobalancing is disabled.\n"); |
26845c28 PM |
64 | #endif |
65 | #ifdef CONFIG_RCU_FAST_NO_HZ | |
efc151c3 | 66 | pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n"); |
26845c28 PM |
67 | #endif |
68 | #ifdef CONFIG_PROVE_RCU | |
efc151c3 | 69 | pr_info("\tRCU lockdep checking is enabled.\n"); |
26845c28 PM |
70 | #endif |
71 | #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE | |
efc151c3 | 72 | pr_info("\tRCU torture testing starts during boot.\n"); |
26845c28 | 73 | #endif |
81a294c4 | 74 | #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE) |
efc151c3 | 75 | pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n"); |
a858af28 PM |
76 | #endif |
77 | #if defined(CONFIG_RCU_CPU_STALL_INFO) | |
efc151c3 | 78 | pr_info("\tAdditional per-CPU info printed with stalls.\n"); |
26845c28 PM |
79 | #endif |
80 | #if NUM_RCU_LVL_4 != 0 | |
efc151c3 | 81 | pr_info("\tFour-level hierarchy is enabled.\n"); |
26845c28 | 82 | #endif |
f885b7f2 | 83 | if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF) |
9a5739d7 | 84 | pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf); |
cca6f393 | 85 | if (nr_cpu_ids != NR_CPUS) |
efc151c3 | 86 | pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids); |
3fbfbf7a | 87 | #ifdef CONFIG_RCU_NOCB_CPU |
911af505 PM |
88 | #ifndef CONFIG_RCU_NOCB_CPU_NONE |
89 | if (!have_rcu_nocb_mask) { | |
615ee544 | 90 | zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL); |
911af505 PM |
91 | have_rcu_nocb_mask = true; |
92 | } | |
93 | #ifdef CONFIG_RCU_NOCB_CPU_ZERO | |
9a5739d7 | 94 | pr_info("\tOffload RCU callbacks from CPU 0\n"); |
911af505 PM |
95 | cpumask_set_cpu(0, rcu_nocb_mask); |
96 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */ | |
97 | #ifdef CONFIG_RCU_NOCB_CPU_ALL | |
9a5739d7 | 98 | pr_info("\tOffload RCU callbacks from all CPUs\n"); |
5d5a0800 | 99 | cpumask_copy(rcu_nocb_mask, cpu_possible_mask); |
911af505 PM |
100 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */ |
101 | #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */ | |
3fbfbf7a | 102 | if (have_rcu_nocb_mask) { |
5d5a0800 KT |
103 | if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { |
104 | pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n"); | |
105 | cpumask_and(rcu_nocb_mask, cpu_possible_mask, | |
106 | rcu_nocb_mask); | |
107 | } | |
3fbfbf7a | 108 | cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask); |
9a5739d7 | 109 | pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf); |
3fbfbf7a | 110 | if (rcu_nocb_poll) |
9a5739d7 | 111 | pr_info("\tPoll for callbacks from no-CBs CPUs.\n"); |
3fbfbf7a PM |
112 | } |
113 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ | |
26845c28 PM |
114 | } |
115 | ||
f41d911f PM |
116 | #ifdef CONFIG_TREE_PREEMPT_RCU |
117 | ||
a41bfeb2 | 118 | RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu); |
27f4d280 | 119 | static struct rcu_state *rcu_state = &rcu_preempt_state; |
f41d911f | 120 | |
d9a3da06 PM |
121 | static int rcu_preempted_readers_exp(struct rcu_node *rnp); |
122 | ||
f41d911f PM |
123 | /* |
124 | * Tell them what RCU they are running. | |
125 | */ | |
0e0fc1c2 | 126 | static void __init rcu_bootup_announce(void) |
f41d911f | 127 | { |
efc151c3 | 128 | pr_info("Preemptible hierarchical RCU implementation.\n"); |
26845c28 | 129 | rcu_bootup_announce_oddness(); |
f41d911f PM |
130 | } |
131 | ||
132 | /* | |
133 | * Return the number of RCU-preempt batches processed thus far | |
134 | * for debug and statistics. | |
135 | */ | |
136 | long rcu_batches_completed_preempt(void) | |
137 | { | |
138 | return rcu_preempt_state.completed; | |
139 | } | |
140 | EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt); | |
141 | ||
142 | /* | |
143 | * Return the number of RCU batches processed thus far for debug & stats. | |
144 | */ | |
145 | long rcu_batches_completed(void) | |
146 | { | |
147 | return rcu_batches_completed_preempt(); | |
148 | } | |
149 | EXPORT_SYMBOL_GPL(rcu_batches_completed); | |
150 | ||
bf66f18e PM |
151 | /* |
152 | * Force a quiescent state for preemptible RCU. | |
153 | */ | |
154 | void rcu_force_quiescent_state(void) | |
155 | { | |
4cdfc175 | 156 | force_quiescent_state(&rcu_preempt_state); |
bf66f18e PM |
157 | } |
158 | EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); | |
159 | ||
f41d911f | 160 | /* |
6cc68793 | 161 | * Record a preemptible-RCU quiescent state for the specified CPU. Note |
f41d911f PM |
162 | * that this just means that the task currently running on the CPU is |
163 | * not in a quiescent state. There might be any number of tasks blocked | |
164 | * while in an RCU read-side critical section. | |
25502a6c PM |
165 | * |
166 | * Unlike the other rcu_*_qs() functions, callers to this function | |
167 | * must disable irqs in order to protect the assignment to | |
168 | * ->rcu_read_unlock_special. | |
f41d911f | 169 | */ |
c3422bea | 170 | static void rcu_preempt_qs(int cpu) |
f41d911f PM |
171 | { |
172 | struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); | |
25502a6c | 173 | |
e4cc1f22 | 174 | if (rdp->passed_quiesce == 0) |
f7f7bac9 | 175 | trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs")); |
e4cc1f22 | 176 | rdp->passed_quiesce = 1; |
25502a6c | 177 | current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; |
f41d911f PM |
178 | } |
179 | ||
180 | /* | |
c3422bea PM |
181 | * We have entered the scheduler, and the current task might soon be |
182 | * context-switched away from. If this task is in an RCU read-side | |
183 | * critical section, we will no longer be able to rely on the CPU to | |
12f5f524 PM |
184 | * record that fact, so we enqueue the task on the blkd_tasks list. |
185 | * The task will dequeue itself when it exits the outermost enclosing | |
186 | * RCU read-side critical section. Therefore, the current grace period | |
187 | * cannot be permitted to complete until the blkd_tasks list entries | |
188 | * predating the current grace period drain, in other words, until | |
189 | * rnp->gp_tasks becomes NULL. | |
c3422bea PM |
190 | * |
191 | * Caller must disable preemption. | |
f41d911f | 192 | */ |
cba6d0d6 | 193 | static void rcu_preempt_note_context_switch(int cpu) |
f41d911f PM |
194 | { |
195 | struct task_struct *t = current; | |
c3422bea | 196 | unsigned long flags; |
f41d911f PM |
197 | struct rcu_data *rdp; |
198 | struct rcu_node *rnp; | |
199 | ||
10f39bb1 | 200 | if (t->rcu_read_lock_nesting > 0 && |
f41d911f PM |
201 | (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { |
202 | ||
203 | /* Possibly blocking in an RCU read-side critical section. */ | |
cba6d0d6 | 204 | rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu); |
f41d911f | 205 | rnp = rdp->mynode; |
1304afb2 | 206 | raw_spin_lock_irqsave(&rnp->lock, flags); |
6303b9c8 | 207 | smp_mb__after_unlock_lock(); |
f41d911f | 208 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; |
86848966 | 209 | t->rcu_blocked_node = rnp; |
f41d911f PM |
210 | |
211 | /* | |
212 | * If this CPU has already checked in, then this task | |
213 | * will hold up the next grace period rather than the | |
214 | * current grace period. Queue the task accordingly. | |
215 | * If the task is queued for the current grace period | |
216 | * (i.e., this CPU has not yet passed through a quiescent | |
217 | * state for the current grace period), then as long | |
218 | * as that task remains queued, the current grace period | |
12f5f524 PM |
219 | * cannot end. Note that there is some uncertainty as |
220 | * to exactly when the current grace period started. | |
221 | * We take a conservative approach, which can result | |
222 | * in unnecessarily waiting on tasks that started very | |
223 | * slightly after the current grace period began. C'est | |
224 | * la vie!!! | |
b0e165c0 PM |
225 | * |
226 | * But first, note that the current CPU must still be | |
227 | * on line! | |
f41d911f | 228 | */ |
b0e165c0 | 229 | WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0); |
e7d8842e | 230 | WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); |
12f5f524 PM |
231 | if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) { |
232 | list_add(&t->rcu_node_entry, rnp->gp_tasks->prev); | |
233 | rnp->gp_tasks = &t->rcu_node_entry; | |
27f4d280 PM |
234 | #ifdef CONFIG_RCU_BOOST |
235 | if (rnp->boost_tasks != NULL) | |
236 | rnp->boost_tasks = rnp->gp_tasks; | |
237 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
12f5f524 PM |
238 | } else { |
239 | list_add(&t->rcu_node_entry, &rnp->blkd_tasks); | |
240 | if (rnp->qsmask & rdp->grpmask) | |
241 | rnp->gp_tasks = &t->rcu_node_entry; | |
242 | } | |
d4c08f2a PM |
243 | trace_rcu_preempt_task(rdp->rsp->name, |
244 | t->pid, | |
245 | (rnp->qsmask & rdp->grpmask) | |
246 | ? rnp->gpnum | |
247 | : rnp->gpnum + 1); | |
1304afb2 | 248 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
10f39bb1 PM |
249 | } else if (t->rcu_read_lock_nesting < 0 && |
250 | t->rcu_read_unlock_special) { | |
251 | ||
252 | /* | |
253 | * Complete exit from RCU read-side critical section on | |
254 | * behalf of preempted instance of __rcu_read_unlock(). | |
255 | */ | |
256 | rcu_read_unlock_special(t); | |
f41d911f PM |
257 | } |
258 | ||
259 | /* | |
260 | * Either we were not in an RCU read-side critical section to | |
261 | * begin with, or we have now recorded that critical section | |
262 | * globally. Either way, we can now note a quiescent state | |
263 | * for this CPU. Again, if we were in an RCU read-side critical | |
264 | * section, and if that critical section was blocking the current | |
265 | * grace period, then the fact that the task has been enqueued | |
266 | * means that we continue to block the current grace period. | |
267 | */ | |
e7d8842e | 268 | local_irq_save(flags); |
cba6d0d6 | 269 | rcu_preempt_qs(cpu); |
e7d8842e | 270 | local_irq_restore(flags); |
f41d911f PM |
271 | } |
272 | ||
fc2219d4 PM |
273 | /* |
274 | * Check for preempted RCU readers blocking the current grace period | |
275 | * for the specified rcu_node structure. If the caller needs a reliable | |
276 | * answer, it must hold the rcu_node's ->lock. | |
277 | */ | |
27f4d280 | 278 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
fc2219d4 | 279 | { |
12f5f524 | 280 | return rnp->gp_tasks != NULL; |
fc2219d4 PM |
281 | } |
282 | ||
b668c9cf PM |
283 | /* |
284 | * Record a quiescent state for all tasks that were previously queued | |
285 | * on the specified rcu_node structure and that were blocking the current | |
286 | * RCU grace period. The caller must hold the specified rnp->lock with | |
287 | * irqs disabled, and this lock is released upon return, but irqs remain | |
288 | * disabled. | |
289 | */ | |
d3f6bad3 | 290 | static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
b668c9cf PM |
291 | __releases(rnp->lock) |
292 | { | |
293 | unsigned long mask; | |
294 | struct rcu_node *rnp_p; | |
295 | ||
27f4d280 | 296 | if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { |
1304afb2 | 297 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b668c9cf PM |
298 | return; /* Still need more quiescent states! */ |
299 | } | |
300 | ||
301 | rnp_p = rnp->parent; | |
302 | if (rnp_p == NULL) { | |
303 | /* | |
304 | * Either there is only one rcu_node in the tree, | |
305 | * or tasks were kicked up to root rcu_node due to | |
306 | * CPUs going offline. | |
307 | */ | |
d3f6bad3 | 308 | rcu_report_qs_rsp(&rcu_preempt_state, flags); |
b668c9cf PM |
309 | return; |
310 | } | |
311 | ||
312 | /* Report up the rest of the hierarchy. */ | |
313 | mask = rnp->grpmask; | |
1304afb2 PM |
314 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
315 | raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */ | |
6303b9c8 | 316 | smp_mb__after_unlock_lock(); |
d3f6bad3 | 317 | rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags); |
b668c9cf PM |
318 | } |
319 | ||
12f5f524 PM |
320 | /* |
321 | * Advance a ->blkd_tasks-list pointer to the next entry, instead | |
322 | * returning NULL if at the end of the list. | |
323 | */ | |
324 | static struct list_head *rcu_next_node_entry(struct task_struct *t, | |
325 | struct rcu_node *rnp) | |
326 | { | |
327 | struct list_head *np; | |
328 | ||
329 | np = t->rcu_node_entry.next; | |
330 | if (np == &rnp->blkd_tasks) | |
331 | np = NULL; | |
332 | return np; | |
333 | } | |
334 | ||
b668c9cf PM |
335 | /* |
336 | * Handle special cases during rcu_read_unlock(), such as needing to | |
337 | * notify RCU core processing or task having blocked during the RCU | |
338 | * read-side critical section. | |
339 | */ | |
2a3fa843 | 340 | void rcu_read_unlock_special(struct task_struct *t) |
f41d911f PM |
341 | { |
342 | int empty; | |
d9a3da06 | 343 | int empty_exp; |
389abd48 | 344 | int empty_exp_now; |
f41d911f | 345 | unsigned long flags; |
12f5f524 | 346 | struct list_head *np; |
82e78d80 PM |
347 | #ifdef CONFIG_RCU_BOOST |
348 | struct rt_mutex *rbmp = NULL; | |
349 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
f41d911f PM |
350 | struct rcu_node *rnp; |
351 | int special; | |
352 | ||
353 | /* NMI handlers cannot block and cannot safely manipulate state. */ | |
354 | if (in_nmi()) | |
355 | return; | |
356 | ||
357 | local_irq_save(flags); | |
358 | ||
359 | /* | |
360 | * If RCU core is waiting for this CPU to exit critical section, | |
361 | * let it know that we have done so. | |
362 | */ | |
363 | special = t->rcu_read_unlock_special; | |
364 | if (special & RCU_READ_UNLOCK_NEED_QS) { | |
c3422bea | 365 | rcu_preempt_qs(smp_processor_id()); |
79a62f95 LJ |
366 | if (!t->rcu_read_unlock_special) { |
367 | local_irq_restore(flags); | |
368 | return; | |
369 | } | |
f41d911f PM |
370 | } |
371 | ||
79a62f95 LJ |
372 | /* Hardware IRQ handlers cannot block, complain if they get here. */ |
373 | if (WARN_ON_ONCE(in_irq() || in_serving_softirq())) { | |
f41d911f PM |
374 | local_irq_restore(flags); |
375 | return; | |
376 | } | |
377 | ||
378 | /* Clean up if blocked during RCU read-side critical section. */ | |
379 | if (special & RCU_READ_UNLOCK_BLOCKED) { | |
380 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; | |
381 | ||
dd5d19ba PM |
382 | /* |
383 | * Remove this task from the list it blocked on. The | |
384 | * task can migrate while we acquire the lock, but at | |
385 | * most one time. So at most two passes through loop. | |
386 | */ | |
387 | for (;;) { | |
86848966 | 388 | rnp = t->rcu_blocked_node; |
1304afb2 | 389 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
6303b9c8 | 390 | smp_mb__after_unlock_lock(); |
86848966 | 391 | if (rnp == t->rcu_blocked_node) |
dd5d19ba | 392 | break; |
1304afb2 | 393 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
dd5d19ba | 394 | } |
27f4d280 | 395 | empty = !rcu_preempt_blocked_readers_cgp(rnp); |
d9a3da06 PM |
396 | empty_exp = !rcu_preempted_readers_exp(rnp); |
397 | smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ | |
12f5f524 | 398 | np = rcu_next_node_entry(t, rnp); |
f41d911f | 399 | list_del_init(&t->rcu_node_entry); |
82e78d80 | 400 | t->rcu_blocked_node = NULL; |
f7f7bac9 | 401 | trace_rcu_unlock_preempted_task(TPS("rcu_preempt"), |
d4c08f2a | 402 | rnp->gpnum, t->pid); |
12f5f524 PM |
403 | if (&t->rcu_node_entry == rnp->gp_tasks) |
404 | rnp->gp_tasks = np; | |
405 | if (&t->rcu_node_entry == rnp->exp_tasks) | |
406 | rnp->exp_tasks = np; | |
27f4d280 PM |
407 | #ifdef CONFIG_RCU_BOOST |
408 | if (&t->rcu_node_entry == rnp->boost_tasks) | |
409 | rnp->boost_tasks = np; | |
82e78d80 PM |
410 | /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */ |
411 | if (t->rcu_boost_mutex) { | |
412 | rbmp = t->rcu_boost_mutex; | |
413 | t->rcu_boost_mutex = NULL; | |
7765be2f | 414 | } |
27f4d280 | 415 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
f41d911f PM |
416 | |
417 | /* | |
418 | * If this was the last task on the current list, and if | |
419 | * we aren't waiting on any CPUs, report the quiescent state. | |
389abd48 PM |
420 | * Note that rcu_report_unblock_qs_rnp() releases rnp->lock, |
421 | * so we must take a snapshot of the expedited state. | |
f41d911f | 422 | */ |
389abd48 | 423 | empty_exp_now = !rcu_preempted_readers_exp(rnp); |
d4c08f2a | 424 | if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) { |
f7f7bac9 | 425 | trace_rcu_quiescent_state_report(TPS("preempt_rcu"), |
d4c08f2a PM |
426 | rnp->gpnum, |
427 | 0, rnp->qsmask, | |
428 | rnp->level, | |
429 | rnp->grplo, | |
430 | rnp->grphi, | |
431 | !!rnp->gp_tasks); | |
d3f6bad3 | 432 | rcu_report_unblock_qs_rnp(rnp, flags); |
c701d5d9 | 433 | } else { |
d4c08f2a | 434 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
c701d5d9 | 435 | } |
d9a3da06 | 436 | |
27f4d280 PM |
437 | #ifdef CONFIG_RCU_BOOST |
438 | /* Unboost if we were boosted. */ | |
82e78d80 PM |
439 | if (rbmp) |
440 | rt_mutex_unlock(rbmp); | |
27f4d280 PM |
441 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
442 | ||
d9a3da06 PM |
443 | /* |
444 | * If this was the last task on the expedited lists, | |
445 | * then we need to report up the rcu_node hierarchy. | |
446 | */ | |
389abd48 | 447 | if (!empty_exp && empty_exp_now) |
b40d293e | 448 | rcu_report_exp_rnp(&rcu_preempt_state, rnp, true); |
b668c9cf PM |
449 | } else { |
450 | local_irq_restore(flags); | |
f41d911f | 451 | } |
f41d911f PM |
452 | } |
453 | ||
1ed509a2 PM |
454 | #ifdef CONFIG_RCU_CPU_STALL_VERBOSE |
455 | ||
456 | /* | |
457 | * Dump detailed information for all tasks blocking the current RCU | |
458 | * grace period on the specified rcu_node structure. | |
459 | */ | |
460 | static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) | |
461 | { | |
462 | unsigned long flags; | |
1ed509a2 PM |
463 | struct task_struct *t; |
464 | ||
12f5f524 | 465 | raw_spin_lock_irqsave(&rnp->lock, flags); |
5fd4dc06 PM |
466 | if (!rcu_preempt_blocked_readers_cgp(rnp)) { |
467 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
468 | return; | |
469 | } | |
12f5f524 PM |
470 | t = list_entry(rnp->gp_tasks, |
471 | struct task_struct, rcu_node_entry); | |
472 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) | |
473 | sched_show_task(t); | |
474 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
1ed509a2 PM |
475 | } |
476 | ||
477 | /* | |
478 | * Dump detailed information for all tasks blocking the current RCU | |
479 | * grace period. | |
480 | */ | |
481 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
482 | { | |
483 | struct rcu_node *rnp = rcu_get_root(rsp); | |
484 | ||
485 | rcu_print_detail_task_stall_rnp(rnp); | |
486 | rcu_for_each_leaf_node(rsp, rnp) | |
487 | rcu_print_detail_task_stall_rnp(rnp); | |
488 | } | |
489 | ||
490 | #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ | |
491 | ||
492 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
493 | { | |
494 | } | |
495 | ||
496 | #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ | |
497 | ||
a858af28 PM |
498 | #ifdef CONFIG_RCU_CPU_STALL_INFO |
499 | ||
500 | static void rcu_print_task_stall_begin(struct rcu_node *rnp) | |
501 | { | |
efc151c3 | 502 | pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", |
a858af28 PM |
503 | rnp->level, rnp->grplo, rnp->grphi); |
504 | } | |
505 | ||
506 | static void rcu_print_task_stall_end(void) | |
507 | { | |
efc151c3 | 508 | pr_cont("\n"); |
a858af28 PM |
509 | } |
510 | ||
511 | #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ | |
512 | ||
513 | static void rcu_print_task_stall_begin(struct rcu_node *rnp) | |
514 | { | |
515 | } | |
516 | ||
517 | static void rcu_print_task_stall_end(void) | |
518 | { | |
519 | } | |
520 | ||
521 | #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */ | |
522 | ||
f41d911f PM |
523 | /* |
524 | * Scan the current list of tasks blocked within RCU read-side critical | |
525 | * sections, printing out the tid of each. | |
526 | */ | |
9bc8b558 | 527 | static int rcu_print_task_stall(struct rcu_node *rnp) |
f41d911f | 528 | { |
f41d911f | 529 | struct task_struct *t; |
9bc8b558 | 530 | int ndetected = 0; |
f41d911f | 531 | |
27f4d280 | 532 | if (!rcu_preempt_blocked_readers_cgp(rnp)) |
9bc8b558 | 533 | return 0; |
a858af28 | 534 | rcu_print_task_stall_begin(rnp); |
12f5f524 PM |
535 | t = list_entry(rnp->gp_tasks, |
536 | struct task_struct, rcu_node_entry); | |
9bc8b558 | 537 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { |
efc151c3 | 538 | pr_cont(" P%d", t->pid); |
9bc8b558 PM |
539 | ndetected++; |
540 | } | |
a858af28 | 541 | rcu_print_task_stall_end(); |
9bc8b558 | 542 | return ndetected; |
f41d911f PM |
543 | } |
544 | ||
b0e165c0 PM |
545 | /* |
546 | * Check that the list of blocked tasks for the newly completed grace | |
547 | * period is in fact empty. It is a serious bug to complete a grace | |
548 | * period that still has RCU readers blocked! This function must be | |
549 | * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock | |
550 | * must be held by the caller. | |
12f5f524 PM |
551 | * |
552 | * Also, if there are blocked tasks on the list, they automatically | |
553 | * block the newly created grace period, so set up ->gp_tasks accordingly. | |
b0e165c0 PM |
554 | */ |
555 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
556 | { | |
27f4d280 | 557 | WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)); |
12f5f524 PM |
558 | if (!list_empty(&rnp->blkd_tasks)) |
559 | rnp->gp_tasks = rnp->blkd_tasks.next; | |
28ecd580 | 560 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
561 | } |
562 | ||
33f76148 PM |
563 | #ifdef CONFIG_HOTPLUG_CPU |
564 | ||
dd5d19ba PM |
565 | /* |
566 | * Handle tasklist migration for case in which all CPUs covered by the | |
567 | * specified rcu_node have gone offline. Move them up to the root | |
568 | * rcu_node. The reason for not just moving them to the immediate | |
569 | * parent is to remove the need for rcu_read_unlock_special() to | |
570 | * make more than two attempts to acquire the target rcu_node's lock. | |
b668c9cf PM |
571 | * Returns true if there were tasks blocking the current RCU grace |
572 | * period. | |
dd5d19ba | 573 | * |
237c80c5 PM |
574 | * Returns 1 if there was previously a task blocking the current grace |
575 | * period on the specified rcu_node structure. | |
576 | * | |
dd5d19ba PM |
577 | * The caller must hold rnp->lock with irqs disabled. |
578 | */ | |
237c80c5 PM |
579 | static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
580 | struct rcu_node *rnp, | |
581 | struct rcu_data *rdp) | |
dd5d19ba | 582 | { |
dd5d19ba PM |
583 | struct list_head *lp; |
584 | struct list_head *lp_root; | |
d9a3da06 | 585 | int retval = 0; |
dd5d19ba | 586 | struct rcu_node *rnp_root = rcu_get_root(rsp); |
12f5f524 | 587 | struct task_struct *t; |
dd5d19ba | 588 | |
86848966 PM |
589 | if (rnp == rnp_root) { |
590 | WARN_ONCE(1, "Last CPU thought to be offlined?"); | |
237c80c5 | 591 | return 0; /* Shouldn't happen: at least one CPU online. */ |
86848966 | 592 | } |
12f5f524 PM |
593 | |
594 | /* If we are on an internal node, complain bitterly. */ | |
595 | WARN_ON_ONCE(rnp != rdp->mynode); | |
dd5d19ba PM |
596 | |
597 | /* | |
12f5f524 PM |
598 | * Move tasks up to root rcu_node. Don't try to get fancy for |
599 | * this corner-case operation -- just put this node's tasks | |
600 | * at the head of the root node's list, and update the root node's | |
601 | * ->gp_tasks and ->exp_tasks pointers to those of this node's, | |
602 | * if non-NULL. This might result in waiting for more tasks than | |
603 | * absolutely necessary, but this is a good performance/complexity | |
604 | * tradeoff. | |
dd5d19ba | 605 | */ |
2036d94a | 606 | if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0) |
d9a3da06 PM |
607 | retval |= RCU_OFL_TASKS_NORM_GP; |
608 | if (rcu_preempted_readers_exp(rnp)) | |
609 | retval |= RCU_OFL_TASKS_EXP_GP; | |
12f5f524 PM |
610 | lp = &rnp->blkd_tasks; |
611 | lp_root = &rnp_root->blkd_tasks; | |
612 | while (!list_empty(lp)) { | |
613 | t = list_entry(lp->next, typeof(*t), rcu_node_entry); | |
614 | raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ | |
6303b9c8 | 615 | smp_mb__after_unlock_lock(); |
12f5f524 PM |
616 | list_del(&t->rcu_node_entry); |
617 | t->rcu_blocked_node = rnp_root; | |
618 | list_add(&t->rcu_node_entry, lp_root); | |
619 | if (&t->rcu_node_entry == rnp->gp_tasks) | |
620 | rnp_root->gp_tasks = rnp->gp_tasks; | |
621 | if (&t->rcu_node_entry == rnp->exp_tasks) | |
622 | rnp_root->exp_tasks = rnp->exp_tasks; | |
27f4d280 PM |
623 | #ifdef CONFIG_RCU_BOOST |
624 | if (&t->rcu_node_entry == rnp->boost_tasks) | |
625 | rnp_root->boost_tasks = rnp->boost_tasks; | |
626 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
12f5f524 | 627 | raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ |
dd5d19ba | 628 | } |
27f4d280 | 629 | |
1e3fd2b3 PM |
630 | rnp->gp_tasks = NULL; |
631 | rnp->exp_tasks = NULL; | |
27f4d280 | 632 | #ifdef CONFIG_RCU_BOOST |
1e3fd2b3 | 633 | rnp->boost_tasks = NULL; |
5cc900cf PM |
634 | /* |
635 | * In case root is being boosted and leaf was not. Make sure | |
636 | * that we boost the tasks blocking the current grace period | |
637 | * in this case. | |
638 | */ | |
27f4d280 | 639 | raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ |
6303b9c8 | 640 | smp_mb__after_unlock_lock(); |
27f4d280 | 641 | if (rnp_root->boost_tasks != NULL && |
5cc900cf PM |
642 | rnp_root->boost_tasks != rnp_root->gp_tasks && |
643 | rnp_root->boost_tasks != rnp_root->exp_tasks) | |
27f4d280 PM |
644 | rnp_root->boost_tasks = rnp_root->gp_tasks; |
645 | raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ | |
646 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
647 | ||
237c80c5 | 648 | return retval; |
dd5d19ba PM |
649 | } |
650 | ||
e5601400 PM |
651 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
652 | ||
f41d911f PM |
653 | /* |
654 | * Check for a quiescent state from the current CPU. When a task blocks, | |
655 | * the task is recorded in the corresponding CPU's rcu_node structure, | |
656 | * which is checked elsewhere. | |
657 | * | |
658 | * Caller must disable hard irqs. | |
659 | */ | |
660 | static void rcu_preempt_check_callbacks(int cpu) | |
661 | { | |
662 | struct task_struct *t = current; | |
663 | ||
664 | if (t->rcu_read_lock_nesting == 0) { | |
c3422bea | 665 | rcu_preempt_qs(cpu); |
f41d911f PM |
666 | return; |
667 | } | |
10f39bb1 PM |
668 | if (t->rcu_read_lock_nesting > 0 && |
669 | per_cpu(rcu_preempt_data, cpu).qs_pending) | |
c3422bea | 670 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; |
f41d911f PM |
671 | } |
672 | ||
a46e0899 PM |
673 | #ifdef CONFIG_RCU_BOOST |
674 | ||
09223371 SL |
675 | static void rcu_preempt_do_callbacks(void) |
676 | { | |
c9d4b0af | 677 | rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data)); |
09223371 SL |
678 | } |
679 | ||
a46e0899 PM |
680 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
681 | ||
f41d911f | 682 | /* |
6cc68793 | 683 | * Queue a preemptible-RCU callback for invocation after a grace period. |
f41d911f PM |
684 | */ |
685 | void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) | |
686 | { | |
3fbfbf7a | 687 | __call_rcu(head, func, &rcu_preempt_state, -1, 0); |
f41d911f PM |
688 | } |
689 | EXPORT_SYMBOL_GPL(call_rcu); | |
690 | ||
486e2593 PM |
691 | /* |
692 | * Queue an RCU callback for lazy invocation after a grace period. | |
693 | * This will likely be later named something like "call_rcu_lazy()", | |
694 | * but this change will require some way of tagging the lazy RCU | |
695 | * callbacks in the list of pending callbacks. Until then, this | |
696 | * function may only be called from __kfree_rcu(). | |
697 | */ | |
698 | void kfree_call_rcu(struct rcu_head *head, | |
699 | void (*func)(struct rcu_head *rcu)) | |
700 | { | |
3fbfbf7a | 701 | __call_rcu(head, func, &rcu_preempt_state, -1, 1); |
486e2593 PM |
702 | } |
703 | EXPORT_SYMBOL_GPL(kfree_call_rcu); | |
704 | ||
6ebb237b PM |
705 | /** |
706 | * synchronize_rcu - wait until a grace period has elapsed. | |
707 | * | |
708 | * Control will return to the caller some time after a full grace | |
709 | * period has elapsed, in other words after all currently executing RCU | |
77d8485a PM |
710 | * read-side critical sections have completed. Note, however, that |
711 | * upon return from synchronize_rcu(), the caller might well be executing | |
712 | * concurrently with new RCU read-side critical sections that began while | |
713 | * synchronize_rcu() was waiting. RCU read-side critical sections are | |
714 | * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. | |
f0a0e6f2 PM |
715 | * |
716 | * See the description of synchronize_sched() for more detailed information | |
717 | * on memory ordering guarantees. | |
6ebb237b PM |
718 | */ |
719 | void synchronize_rcu(void) | |
720 | { | |
fe15d706 PM |
721 | rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && |
722 | !lock_is_held(&rcu_lock_map) && | |
723 | !lock_is_held(&rcu_sched_lock_map), | |
724 | "Illegal synchronize_rcu() in RCU read-side critical section"); | |
6ebb237b PM |
725 | if (!rcu_scheduler_active) |
726 | return; | |
3705b88d AM |
727 | if (rcu_expedited) |
728 | synchronize_rcu_expedited(); | |
729 | else | |
730 | wait_rcu_gp(call_rcu); | |
6ebb237b PM |
731 | } |
732 | EXPORT_SYMBOL_GPL(synchronize_rcu); | |
733 | ||
d9a3da06 | 734 | static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); |
bcfa57ce | 735 | static unsigned long sync_rcu_preempt_exp_count; |
d9a3da06 PM |
736 | static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); |
737 | ||
738 | /* | |
739 | * Return non-zero if there are any tasks in RCU read-side critical | |
740 | * sections blocking the current preemptible-RCU expedited grace period. | |
741 | * If there is no preemptible-RCU expedited grace period currently in | |
742 | * progress, returns zero unconditionally. | |
743 | */ | |
744 | static int rcu_preempted_readers_exp(struct rcu_node *rnp) | |
745 | { | |
12f5f524 | 746 | return rnp->exp_tasks != NULL; |
d9a3da06 PM |
747 | } |
748 | ||
749 | /* | |
750 | * return non-zero if there is no RCU expedited grace period in progress | |
751 | * for the specified rcu_node structure, in other words, if all CPUs and | |
752 | * tasks covered by the specified rcu_node structure have done their bit | |
753 | * for the current expedited grace period. Works only for preemptible | |
754 | * RCU -- other RCU implementation use other means. | |
755 | * | |
756 | * Caller must hold sync_rcu_preempt_exp_mutex. | |
757 | */ | |
758 | static int sync_rcu_preempt_exp_done(struct rcu_node *rnp) | |
759 | { | |
760 | return !rcu_preempted_readers_exp(rnp) && | |
761 | ACCESS_ONCE(rnp->expmask) == 0; | |
762 | } | |
763 | ||
764 | /* | |
765 | * Report the exit from RCU read-side critical section for the last task | |
766 | * that queued itself during or before the current expedited preemptible-RCU | |
767 | * grace period. This event is reported either to the rcu_node structure on | |
768 | * which the task was queued or to one of that rcu_node structure's ancestors, | |
769 | * recursively up the tree. (Calm down, calm down, we do the recursion | |
770 | * iteratively!) | |
771 | * | |
b40d293e TG |
772 | * Most callers will set the "wake" flag, but the task initiating the |
773 | * expedited grace period need not wake itself. | |
774 | * | |
d9a3da06 PM |
775 | * Caller must hold sync_rcu_preempt_exp_mutex. |
776 | */ | |
b40d293e TG |
777 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, |
778 | bool wake) | |
d9a3da06 PM |
779 | { |
780 | unsigned long flags; | |
781 | unsigned long mask; | |
782 | ||
1304afb2 | 783 | raw_spin_lock_irqsave(&rnp->lock, flags); |
6303b9c8 | 784 | smp_mb__after_unlock_lock(); |
d9a3da06 | 785 | for (;;) { |
131906b0 PM |
786 | if (!sync_rcu_preempt_exp_done(rnp)) { |
787 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
d9a3da06 | 788 | break; |
131906b0 | 789 | } |
d9a3da06 | 790 | if (rnp->parent == NULL) { |
131906b0 | 791 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
78e4bc34 PM |
792 | if (wake) { |
793 | smp_mb(); /* EGP done before wake_up(). */ | |
b40d293e | 794 | wake_up(&sync_rcu_preempt_exp_wq); |
78e4bc34 | 795 | } |
d9a3da06 PM |
796 | break; |
797 | } | |
798 | mask = rnp->grpmask; | |
1304afb2 | 799 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ |
d9a3da06 | 800 | rnp = rnp->parent; |
1304afb2 | 801 | raw_spin_lock(&rnp->lock); /* irqs already disabled */ |
6303b9c8 | 802 | smp_mb__after_unlock_lock(); |
d9a3da06 PM |
803 | rnp->expmask &= ~mask; |
804 | } | |
d9a3da06 PM |
805 | } |
806 | ||
807 | /* | |
808 | * Snapshot the tasks blocking the newly started preemptible-RCU expedited | |
809 | * grace period for the specified rcu_node structure. If there are no such | |
810 | * tasks, report it up the rcu_node hierarchy. | |
811 | * | |
7b2e6011 PM |
812 | * Caller must hold sync_rcu_preempt_exp_mutex and must exclude |
813 | * CPU hotplug operations. | |
d9a3da06 PM |
814 | */ |
815 | static void | |
816 | sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) | |
817 | { | |
1217ed1b | 818 | unsigned long flags; |
12f5f524 | 819 | int must_wait = 0; |
d9a3da06 | 820 | |
1217ed1b | 821 | raw_spin_lock_irqsave(&rnp->lock, flags); |
6303b9c8 | 822 | smp_mb__after_unlock_lock(); |
c701d5d9 | 823 | if (list_empty(&rnp->blkd_tasks)) { |
1217ed1b | 824 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
c701d5d9 | 825 | } else { |
12f5f524 | 826 | rnp->exp_tasks = rnp->blkd_tasks.next; |
1217ed1b | 827 | rcu_initiate_boost(rnp, flags); /* releases rnp->lock */ |
12f5f524 PM |
828 | must_wait = 1; |
829 | } | |
d9a3da06 | 830 | if (!must_wait) |
b40d293e | 831 | rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */ |
d9a3da06 PM |
832 | } |
833 | ||
236fefaf PM |
834 | /** |
835 | * synchronize_rcu_expedited - Brute-force RCU grace period | |
836 | * | |
837 | * Wait for an RCU-preempt grace period, but expedite it. The basic | |
838 | * idea is to invoke synchronize_sched_expedited() to push all the tasks to | |
839 | * the ->blkd_tasks lists and wait for this list to drain. This consumes | |
840 | * significant time on all CPUs and is unfriendly to real-time workloads, | |
841 | * so is thus not recommended for any sort of common-case code. | |
842 | * In fact, if you are using synchronize_rcu_expedited() in a loop, | |
843 | * please restructure your code to batch your updates, and then Use a | |
844 | * single synchronize_rcu() instead. | |
845 | * | |
846 | * Note that it is illegal to call this function while holding any lock | |
847 | * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal | |
848 | * to call this function from a CPU-hotplug notifier. Failing to observe | |
849 | * these restriction will result in deadlock. | |
019129d5 PM |
850 | */ |
851 | void synchronize_rcu_expedited(void) | |
852 | { | |
d9a3da06 PM |
853 | unsigned long flags; |
854 | struct rcu_node *rnp; | |
855 | struct rcu_state *rsp = &rcu_preempt_state; | |
bcfa57ce | 856 | unsigned long snap; |
d9a3da06 PM |
857 | int trycount = 0; |
858 | ||
859 | smp_mb(); /* Caller's modifications seen first by other CPUs. */ | |
860 | snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1; | |
861 | smp_mb(); /* Above access cannot bleed into critical section. */ | |
862 | ||
1943c89d PM |
863 | /* |
864 | * Block CPU-hotplug operations. This means that any CPU-hotplug | |
865 | * operation that finds an rcu_node structure with tasks in the | |
866 | * process of being boosted will know that all tasks blocking | |
867 | * this expedited grace period will already be in the process of | |
868 | * being boosted. This simplifies the process of moving tasks | |
869 | * from leaf to root rcu_node structures. | |
870 | */ | |
871 | get_online_cpus(); | |
872 | ||
d9a3da06 PM |
873 | /* |
874 | * Acquire lock, falling back to synchronize_rcu() if too many | |
875 | * lock-acquisition failures. Of course, if someone does the | |
876 | * expedited grace period for us, just leave. | |
877 | */ | |
878 | while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) { | |
1943c89d PM |
879 | if (ULONG_CMP_LT(snap, |
880 | ACCESS_ONCE(sync_rcu_preempt_exp_count))) { | |
881 | put_online_cpus(); | |
882 | goto mb_ret; /* Others did our work for us. */ | |
883 | } | |
c701d5d9 | 884 | if (trycount++ < 10) { |
d9a3da06 | 885 | udelay(trycount * num_online_cpus()); |
c701d5d9 | 886 | } else { |
1943c89d | 887 | put_online_cpus(); |
3705b88d | 888 | wait_rcu_gp(call_rcu); |
d9a3da06 PM |
889 | return; |
890 | } | |
d9a3da06 | 891 | } |
1943c89d PM |
892 | if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) { |
893 | put_online_cpus(); | |
d9a3da06 | 894 | goto unlock_mb_ret; /* Others did our work for us. */ |
1943c89d | 895 | } |
d9a3da06 | 896 | |
12f5f524 | 897 | /* force all RCU readers onto ->blkd_tasks lists. */ |
d9a3da06 PM |
898 | synchronize_sched_expedited(); |
899 | ||
d9a3da06 PM |
900 | /* Initialize ->expmask for all non-leaf rcu_node structures. */ |
901 | rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) { | |
1943c89d | 902 | raw_spin_lock_irqsave(&rnp->lock, flags); |
6303b9c8 | 903 | smp_mb__after_unlock_lock(); |
d9a3da06 | 904 | rnp->expmask = rnp->qsmaskinit; |
1943c89d | 905 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
d9a3da06 PM |
906 | } |
907 | ||
12f5f524 | 908 | /* Snapshot current state of ->blkd_tasks lists. */ |
d9a3da06 PM |
909 | rcu_for_each_leaf_node(rsp, rnp) |
910 | sync_rcu_preempt_exp_init(rsp, rnp); | |
911 | if (NUM_RCU_NODES > 1) | |
912 | sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp)); | |
913 | ||
1943c89d | 914 | put_online_cpus(); |
d9a3da06 | 915 | |
12f5f524 | 916 | /* Wait for snapshotted ->blkd_tasks lists to drain. */ |
d9a3da06 PM |
917 | rnp = rcu_get_root(rsp); |
918 | wait_event(sync_rcu_preempt_exp_wq, | |
919 | sync_rcu_preempt_exp_done(rnp)); | |
920 | ||
921 | /* Clean up and exit. */ | |
922 | smp_mb(); /* ensure expedited GP seen before counter increment. */ | |
923 | ACCESS_ONCE(sync_rcu_preempt_exp_count)++; | |
924 | unlock_mb_ret: | |
925 | mutex_unlock(&sync_rcu_preempt_exp_mutex); | |
926 | mb_ret: | |
927 | smp_mb(); /* ensure subsequent action seen after grace period. */ | |
019129d5 PM |
928 | } |
929 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
930 | ||
e74f4c45 PM |
931 | /** |
932 | * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. | |
f0a0e6f2 PM |
933 | * |
934 | * Note that this primitive does not necessarily wait for an RCU grace period | |
935 | * to complete. For example, if there are no RCU callbacks queued anywhere | |
936 | * in the system, then rcu_barrier() is within its rights to return | |
937 | * immediately, without waiting for anything, much less an RCU grace period. | |
e74f4c45 PM |
938 | */ |
939 | void rcu_barrier(void) | |
940 | { | |
037b64ed | 941 | _rcu_barrier(&rcu_preempt_state); |
e74f4c45 PM |
942 | } |
943 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
944 | ||
1eba8f84 | 945 | /* |
6cc68793 | 946 | * Initialize preemptible RCU's state structures. |
1eba8f84 PM |
947 | */ |
948 | static void __init __rcu_init_preempt(void) | |
949 | { | |
394f99a9 | 950 | rcu_init_one(&rcu_preempt_state, &rcu_preempt_data); |
1eba8f84 PM |
951 | } |
952 | ||
2439b696 PM |
953 | /* |
954 | * Check for a task exiting while in a preemptible-RCU read-side | |
955 | * critical section, clean up if so. No need to issue warnings, | |
956 | * as debug_check_no_locks_held() already does this if lockdep | |
957 | * is enabled. | |
958 | */ | |
959 | void exit_rcu(void) | |
960 | { | |
961 | struct task_struct *t = current; | |
962 | ||
963 | if (likely(list_empty(¤t->rcu_node_entry))) | |
964 | return; | |
965 | t->rcu_read_lock_nesting = 1; | |
966 | barrier(); | |
967 | t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED; | |
968 | __rcu_read_unlock(); | |
969 | } | |
970 | ||
f41d911f PM |
971 | #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ |
972 | ||
27f4d280 PM |
973 | static struct rcu_state *rcu_state = &rcu_sched_state; |
974 | ||
f41d911f PM |
975 | /* |
976 | * Tell them what RCU they are running. | |
977 | */ | |
0e0fc1c2 | 978 | static void __init rcu_bootup_announce(void) |
f41d911f | 979 | { |
efc151c3 | 980 | pr_info("Hierarchical RCU implementation.\n"); |
26845c28 | 981 | rcu_bootup_announce_oddness(); |
f41d911f PM |
982 | } |
983 | ||
984 | /* | |
985 | * Return the number of RCU batches processed thus far for debug & stats. | |
986 | */ | |
987 | long rcu_batches_completed(void) | |
988 | { | |
989 | return rcu_batches_completed_sched(); | |
990 | } | |
991 | EXPORT_SYMBOL_GPL(rcu_batches_completed); | |
992 | ||
bf66f18e PM |
993 | /* |
994 | * Force a quiescent state for RCU, which, because there is no preemptible | |
995 | * RCU, becomes the same as rcu-sched. | |
996 | */ | |
997 | void rcu_force_quiescent_state(void) | |
998 | { | |
999 | rcu_sched_force_quiescent_state(); | |
1000 | } | |
1001 | EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); | |
1002 | ||
cba6d0d6 PM |
1003 | /* |
1004 | * Because preemptible RCU does not exist, we never have to check for | |
1005 | * CPUs being in quiescent states. | |
1006 | */ | |
1007 | static void rcu_preempt_note_context_switch(int cpu) | |
1008 | { | |
1009 | } | |
1010 | ||
fc2219d4 | 1011 | /* |
6cc68793 | 1012 | * Because preemptible RCU does not exist, there are never any preempted |
fc2219d4 PM |
1013 | * RCU readers. |
1014 | */ | |
27f4d280 | 1015 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
fc2219d4 PM |
1016 | { |
1017 | return 0; | |
1018 | } | |
1019 | ||
b668c9cf PM |
1020 | #ifdef CONFIG_HOTPLUG_CPU |
1021 | ||
1022 | /* Because preemptible RCU does not exist, no quieting of tasks. */ | |
d3f6bad3 | 1023 | static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
b668c9cf | 1024 | { |
1304afb2 | 1025 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b668c9cf PM |
1026 | } |
1027 | ||
1028 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
1029 | ||
1ed509a2 | 1030 | /* |
6cc68793 | 1031 | * Because preemptible RCU does not exist, we never have to check for |
1ed509a2 PM |
1032 | * tasks blocked within RCU read-side critical sections. |
1033 | */ | |
1034 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
1035 | { | |
1036 | } | |
1037 | ||
f41d911f | 1038 | /* |
6cc68793 | 1039 | * Because preemptible RCU does not exist, we never have to check for |
f41d911f PM |
1040 | * tasks blocked within RCU read-side critical sections. |
1041 | */ | |
9bc8b558 | 1042 | static int rcu_print_task_stall(struct rcu_node *rnp) |
f41d911f | 1043 | { |
9bc8b558 | 1044 | return 0; |
f41d911f PM |
1045 | } |
1046 | ||
b0e165c0 | 1047 | /* |
6cc68793 | 1048 | * Because there is no preemptible RCU, there can be no readers blocked, |
49e29126 PM |
1049 | * so there is no need to check for blocked tasks. So check only for |
1050 | * bogus qsmask values. | |
b0e165c0 PM |
1051 | */ |
1052 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
1053 | { | |
49e29126 | 1054 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
1055 | } |
1056 | ||
33f76148 PM |
1057 | #ifdef CONFIG_HOTPLUG_CPU |
1058 | ||
dd5d19ba | 1059 | /* |
6cc68793 | 1060 | * Because preemptible RCU does not exist, it never needs to migrate |
237c80c5 PM |
1061 | * tasks that were blocked within RCU read-side critical sections, and |
1062 | * such non-existent tasks cannot possibly have been blocking the current | |
1063 | * grace period. | |
dd5d19ba | 1064 | */ |
237c80c5 PM |
1065 | static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
1066 | struct rcu_node *rnp, | |
1067 | struct rcu_data *rdp) | |
dd5d19ba | 1068 | { |
237c80c5 | 1069 | return 0; |
dd5d19ba PM |
1070 | } |
1071 | ||
e5601400 PM |
1072 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
1073 | ||
f41d911f | 1074 | /* |
6cc68793 | 1075 | * Because preemptible RCU does not exist, it never has any callbacks |
f41d911f PM |
1076 | * to check. |
1077 | */ | |
1eba8f84 | 1078 | static void rcu_preempt_check_callbacks(int cpu) |
f41d911f PM |
1079 | { |
1080 | } | |
1081 | ||
486e2593 PM |
1082 | /* |
1083 | * Queue an RCU callback for lazy invocation after a grace period. | |
1084 | * This will likely be later named something like "call_rcu_lazy()", | |
1085 | * but this change will require some way of tagging the lazy RCU | |
1086 | * callbacks in the list of pending callbacks. Until then, this | |
1087 | * function may only be called from __kfree_rcu(). | |
1088 | * | |
1089 | * Because there is no preemptible RCU, we use RCU-sched instead. | |
1090 | */ | |
1091 | void kfree_call_rcu(struct rcu_head *head, | |
1092 | void (*func)(struct rcu_head *rcu)) | |
1093 | { | |
3fbfbf7a | 1094 | __call_rcu(head, func, &rcu_sched_state, -1, 1); |
486e2593 PM |
1095 | } |
1096 | EXPORT_SYMBOL_GPL(kfree_call_rcu); | |
1097 | ||
019129d5 PM |
1098 | /* |
1099 | * Wait for an rcu-preempt grace period, but make it happen quickly. | |
6cc68793 | 1100 | * But because preemptible RCU does not exist, map to rcu-sched. |
019129d5 PM |
1101 | */ |
1102 | void synchronize_rcu_expedited(void) | |
1103 | { | |
1104 | synchronize_sched_expedited(); | |
1105 | } | |
1106 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
1107 | ||
d9a3da06 PM |
1108 | #ifdef CONFIG_HOTPLUG_CPU |
1109 | ||
1110 | /* | |
6cc68793 | 1111 | * Because preemptible RCU does not exist, there is never any need to |
d9a3da06 PM |
1112 | * report on tasks preempted in RCU read-side critical sections during |
1113 | * expedited RCU grace periods. | |
1114 | */ | |
b40d293e TG |
1115 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, |
1116 | bool wake) | |
d9a3da06 | 1117 | { |
d9a3da06 PM |
1118 | } |
1119 | ||
1120 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
1121 | ||
e74f4c45 | 1122 | /* |
6cc68793 | 1123 | * Because preemptible RCU does not exist, rcu_barrier() is just |
e74f4c45 PM |
1124 | * another name for rcu_barrier_sched(). |
1125 | */ | |
1126 | void rcu_barrier(void) | |
1127 | { | |
1128 | rcu_barrier_sched(); | |
1129 | } | |
1130 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
1131 | ||
1eba8f84 | 1132 | /* |
6cc68793 | 1133 | * Because preemptible RCU does not exist, it need not be initialized. |
1eba8f84 PM |
1134 | */ |
1135 | static void __init __rcu_init_preempt(void) | |
1136 | { | |
1137 | } | |
1138 | ||
2439b696 PM |
1139 | /* |
1140 | * Because preemptible RCU does not exist, tasks cannot possibly exit | |
1141 | * while in preemptible RCU read-side critical sections. | |
1142 | */ | |
1143 | void exit_rcu(void) | |
1144 | { | |
1145 | } | |
1146 | ||
f41d911f | 1147 | #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ |
8bd93a2c | 1148 | |
27f4d280 PM |
1149 | #ifdef CONFIG_RCU_BOOST |
1150 | ||
1696a8be | 1151 | #include "../locking/rtmutex_common.h" |
27f4d280 | 1152 | |
0ea1f2eb PM |
1153 | #ifdef CONFIG_RCU_TRACE |
1154 | ||
1155 | static void rcu_initiate_boost_trace(struct rcu_node *rnp) | |
1156 | { | |
1157 | if (list_empty(&rnp->blkd_tasks)) | |
1158 | rnp->n_balk_blkd_tasks++; | |
1159 | else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL) | |
1160 | rnp->n_balk_exp_gp_tasks++; | |
1161 | else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL) | |
1162 | rnp->n_balk_boost_tasks++; | |
1163 | else if (rnp->gp_tasks != NULL && rnp->qsmask != 0) | |
1164 | rnp->n_balk_notblocked++; | |
1165 | else if (rnp->gp_tasks != NULL && | |
a9f4793d | 1166 | ULONG_CMP_LT(jiffies, rnp->boost_time)) |
0ea1f2eb PM |
1167 | rnp->n_balk_notyet++; |
1168 | else | |
1169 | rnp->n_balk_nos++; | |
1170 | } | |
1171 | ||
1172 | #else /* #ifdef CONFIG_RCU_TRACE */ | |
1173 | ||
1174 | static void rcu_initiate_boost_trace(struct rcu_node *rnp) | |
1175 | { | |
1176 | } | |
1177 | ||
1178 | #endif /* #else #ifdef CONFIG_RCU_TRACE */ | |
1179 | ||
5d01bbd1 TG |
1180 | static void rcu_wake_cond(struct task_struct *t, int status) |
1181 | { | |
1182 | /* | |
1183 | * If the thread is yielding, only wake it when this | |
1184 | * is invoked from idle | |
1185 | */ | |
1186 | if (status != RCU_KTHREAD_YIELDING || is_idle_task(current)) | |
1187 | wake_up_process(t); | |
1188 | } | |
1189 | ||
27f4d280 PM |
1190 | /* |
1191 | * Carry out RCU priority boosting on the task indicated by ->exp_tasks | |
1192 | * or ->boost_tasks, advancing the pointer to the next task in the | |
1193 | * ->blkd_tasks list. | |
1194 | * | |
1195 | * Note that irqs must be enabled: boosting the task can block. | |
1196 | * Returns 1 if there are more tasks needing to be boosted. | |
1197 | */ | |
1198 | static int rcu_boost(struct rcu_node *rnp) | |
1199 | { | |
1200 | unsigned long flags; | |
1201 | struct rt_mutex mtx; | |
1202 | struct task_struct *t; | |
1203 | struct list_head *tb; | |
1204 | ||
1205 | if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) | |
1206 | return 0; /* Nothing left to boost. */ | |
1207 | ||
1208 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
6303b9c8 | 1209 | smp_mb__after_unlock_lock(); |
27f4d280 PM |
1210 | |
1211 | /* | |
1212 | * Recheck under the lock: all tasks in need of boosting | |
1213 | * might exit their RCU read-side critical sections on their own. | |
1214 | */ | |
1215 | if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { | |
1216 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
1217 | return 0; | |
1218 | } | |
1219 | ||
1220 | /* | |
1221 | * Preferentially boost tasks blocking expedited grace periods. | |
1222 | * This cannot starve the normal grace periods because a second | |
1223 | * expedited grace period must boost all blocked tasks, including | |
1224 | * those blocking the pre-existing normal grace period. | |
1225 | */ | |
0ea1f2eb | 1226 | if (rnp->exp_tasks != NULL) { |
27f4d280 | 1227 | tb = rnp->exp_tasks; |
0ea1f2eb PM |
1228 | rnp->n_exp_boosts++; |
1229 | } else { | |
27f4d280 | 1230 | tb = rnp->boost_tasks; |
0ea1f2eb PM |
1231 | rnp->n_normal_boosts++; |
1232 | } | |
1233 | rnp->n_tasks_boosted++; | |
27f4d280 PM |
1234 | |
1235 | /* | |
1236 | * We boost task t by manufacturing an rt_mutex that appears to | |
1237 | * be held by task t. We leave a pointer to that rt_mutex where | |
1238 | * task t can find it, and task t will release the mutex when it | |
1239 | * exits its outermost RCU read-side critical section. Then | |
1240 | * simply acquiring this artificial rt_mutex will boost task | |
1241 | * t's priority. (Thanks to tglx for suggesting this approach!) | |
1242 | * | |
1243 | * Note that task t must acquire rnp->lock to remove itself from | |
1244 | * the ->blkd_tasks list, which it will do from exit() if from | |
1245 | * nowhere else. We therefore are guaranteed that task t will | |
1246 | * stay around at least until we drop rnp->lock. Note that | |
1247 | * rnp->lock also resolves races between our priority boosting | |
1248 | * and task t's exiting its outermost RCU read-side critical | |
1249 | * section. | |
1250 | */ | |
1251 | t = container_of(tb, struct task_struct, rcu_node_entry); | |
1252 | rt_mutex_init_proxy_locked(&mtx, t); | |
1253 | t->rcu_boost_mutex = &mtx; | |
27f4d280 PM |
1254 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1255 | rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */ | |
1256 | rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ | |
1257 | ||
4f89b336 PM |
1258 | return ACCESS_ONCE(rnp->exp_tasks) != NULL || |
1259 | ACCESS_ONCE(rnp->boost_tasks) != NULL; | |
27f4d280 PM |
1260 | } |
1261 | ||
27f4d280 PM |
1262 | /* |
1263 | * Priority-boosting kthread. One per leaf rcu_node and one for the | |
1264 | * root rcu_node. | |
1265 | */ | |
1266 | static int rcu_boost_kthread(void *arg) | |
1267 | { | |
1268 | struct rcu_node *rnp = (struct rcu_node *)arg; | |
1269 | int spincnt = 0; | |
1270 | int more2boost; | |
1271 | ||
f7f7bac9 | 1272 | trace_rcu_utilization(TPS("Start boost kthread@init")); |
27f4d280 | 1273 | for (;;) { |
d71df90e | 1274 | rnp->boost_kthread_status = RCU_KTHREAD_WAITING; |
f7f7bac9 | 1275 | trace_rcu_utilization(TPS("End boost kthread@rcu_wait")); |
08bca60a | 1276 | rcu_wait(rnp->boost_tasks || rnp->exp_tasks); |
f7f7bac9 | 1277 | trace_rcu_utilization(TPS("Start boost kthread@rcu_wait")); |
d71df90e | 1278 | rnp->boost_kthread_status = RCU_KTHREAD_RUNNING; |
27f4d280 PM |
1279 | more2boost = rcu_boost(rnp); |
1280 | if (more2boost) | |
1281 | spincnt++; | |
1282 | else | |
1283 | spincnt = 0; | |
1284 | if (spincnt > 10) { | |
5d01bbd1 | 1285 | rnp->boost_kthread_status = RCU_KTHREAD_YIELDING; |
f7f7bac9 | 1286 | trace_rcu_utilization(TPS("End boost kthread@rcu_yield")); |
5d01bbd1 | 1287 | schedule_timeout_interruptible(2); |
f7f7bac9 | 1288 | trace_rcu_utilization(TPS("Start boost kthread@rcu_yield")); |
27f4d280 PM |
1289 | spincnt = 0; |
1290 | } | |
1291 | } | |
1217ed1b | 1292 | /* NOTREACHED */ |
f7f7bac9 | 1293 | trace_rcu_utilization(TPS("End boost kthread@notreached")); |
27f4d280 PM |
1294 | return 0; |
1295 | } | |
1296 | ||
1297 | /* | |
1298 | * Check to see if it is time to start boosting RCU readers that are | |
1299 | * blocking the current grace period, and, if so, tell the per-rcu_node | |
1300 | * kthread to start boosting them. If there is an expedited grace | |
1301 | * period in progress, it is always time to boost. | |
1302 | * | |
b065a853 PM |
1303 | * The caller must hold rnp->lock, which this function releases. |
1304 | * The ->boost_kthread_task is immortal, so we don't need to worry | |
1305 | * about it going away. | |
27f4d280 | 1306 | */ |
1217ed1b | 1307 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
27f4d280 PM |
1308 | { |
1309 | struct task_struct *t; | |
1310 | ||
0ea1f2eb PM |
1311 | if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { |
1312 | rnp->n_balk_exp_gp_tasks++; | |
1217ed1b | 1313 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 | 1314 | return; |
0ea1f2eb | 1315 | } |
27f4d280 PM |
1316 | if (rnp->exp_tasks != NULL || |
1317 | (rnp->gp_tasks != NULL && | |
1318 | rnp->boost_tasks == NULL && | |
1319 | rnp->qsmask == 0 && | |
1320 | ULONG_CMP_GE(jiffies, rnp->boost_time))) { | |
1321 | if (rnp->exp_tasks == NULL) | |
1322 | rnp->boost_tasks = rnp->gp_tasks; | |
1217ed1b | 1323 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 | 1324 | t = rnp->boost_kthread_task; |
5d01bbd1 TG |
1325 | if (t) |
1326 | rcu_wake_cond(t, rnp->boost_kthread_status); | |
1217ed1b | 1327 | } else { |
0ea1f2eb | 1328 | rcu_initiate_boost_trace(rnp); |
1217ed1b PM |
1329 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1330 | } | |
27f4d280 PM |
1331 | } |
1332 | ||
a46e0899 PM |
1333 | /* |
1334 | * Wake up the per-CPU kthread to invoke RCU callbacks. | |
1335 | */ | |
1336 | static void invoke_rcu_callbacks_kthread(void) | |
1337 | { | |
1338 | unsigned long flags; | |
1339 | ||
1340 | local_irq_save(flags); | |
1341 | __this_cpu_write(rcu_cpu_has_work, 1); | |
1eb52121 | 1342 | if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && |
5d01bbd1 TG |
1343 | current != __this_cpu_read(rcu_cpu_kthread_task)) { |
1344 | rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task), | |
1345 | __this_cpu_read(rcu_cpu_kthread_status)); | |
1346 | } | |
a46e0899 PM |
1347 | local_irq_restore(flags); |
1348 | } | |
1349 | ||
dff1672d PM |
1350 | /* |
1351 | * Is the current CPU running the RCU-callbacks kthread? | |
1352 | * Caller must have preemption disabled. | |
1353 | */ | |
1354 | static bool rcu_is_callbacks_kthread(void) | |
1355 | { | |
c9d4b0af | 1356 | return __this_cpu_read(rcu_cpu_kthread_task) == current; |
dff1672d PM |
1357 | } |
1358 | ||
27f4d280 PM |
1359 | #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) |
1360 | ||
1361 | /* | |
1362 | * Do priority-boost accounting for the start of a new grace period. | |
1363 | */ | |
1364 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) | |
1365 | { | |
1366 | rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; | |
1367 | } | |
1368 | ||
27f4d280 PM |
1369 | /* |
1370 | * Create an RCU-boost kthread for the specified node if one does not | |
1371 | * already exist. We only create this kthread for preemptible RCU. | |
1372 | * Returns zero if all is well, a negated errno otherwise. | |
1373 | */ | |
49fb4c62 | 1374 | static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp, |
5d01bbd1 | 1375 | struct rcu_node *rnp) |
27f4d280 | 1376 | { |
5d01bbd1 | 1377 | int rnp_index = rnp - &rsp->node[0]; |
27f4d280 PM |
1378 | unsigned long flags; |
1379 | struct sched_param sp; | |
1380 | struct task_struct *t; | |
1381 | ||
1382 | if (&rcu_preempt_state != rsp) | |
1383 | return 0; | |
5d01bbd1 TG |
1384 | |
1385 | if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0) | |
1386 | return 0; | |
1387 | ||
a46e0899 | 1388 | rsp->boost = 1; |
27f4d280 PM |
1389 | if (rnp->boost_kthread_task != NULL) |
1390 | return 0; | |
1391 | t = kthread_create(rcu_boost_kthread, (void *)rnp, | |
5b61b0ba | 1392 | "rcub/%d", rnp_index); |
27f4d280 PM |
1393 | if (IS_ERR(t)) |
1394 | return PTR_ERR(t); | |
1395 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
6303b9c8 | 1396 | smp_mb__after_unlock_lock(); |
27f4d280 PM |
1397 | rnp->boost_kthread_task = t; |
1398 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
5b61b0ba | 1399 | sp.sched_priority = RCU_BOOST_PRIO; |
27f4d280 | 1400 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); |
9a432736 | 1401 | wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ |
27f4d280 PM |
1402 | return 0; |
1403 | } | |
1404 | ||
f8b7fc6b PM |
1405 | static void rcu_kthread_do_work(void) |
1406 | { | |
c9d4b0af CL |
1407 | rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data)); |
1408 | rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data)); | |
f8b7fc6b PM |
1409 | rcu_preempt_do_callbacks(); |
1410 | } | |
1411 | ||
62ab7072 | 1412 | static void rcu_cpu_kthread_setup(unsigned int cpu) |
f8b7fc6b | 1413 | { |
f8b7fc6b | 1414 | struct sched_param sp; |
f8b7fc6b | 1415 | |
62ab7072 PM |
1416 | sp.sched_priority = RCU_KTHREAD_PRIO; |
1417 | sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); | |
f8b7fc6b PM |
1418 | } |
1419 | ||
62ab7072 | 1420 | static void rcu_cpu_kthread_park(unsigned int cpu) |
f8b7fc6b | 1421 | { |
62ab7072 | 1422 | per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; |
f8b7fc6b PM |
1423 | } |
1424 | ||
62ab7072 | 1425 | static int rcu_cpu_kthread_should_run(unsigned int cpu) |
f8b7fc6b | 1426 | { |
c9d4b0af | 1427 | return __this_cpu_read(rcu_cpu_has_work); |
f8b7fc6b PM |
1428 | } |
1429 | ||
1430 | /* | |
1431 | * Per-CPU kernel thread that invokes RCU callbacks. This replaces the | |
e0f23060 PM |
1432 | * RCU softirq used in flavors and configurations of RCU that do not |
1433 | * support RCU priority boosting. | |
f8b7fc6b | 1434 | */ |
62ab7072 | 1435 | static void rcu_cpu_kthread(unsigned int cpu) |
f8b7fc6b | 1436 | { |
c9d4b0af CL |
1437 | unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status); |
1438 | char work, *workp = this_cpu_ptr(&rcu_cpu_has_work); | |
62ab7072 | 1439 | int spincnt; |
f8b7fc6b | 1440 | |
62ab7072 | 1441 | for (spincnt = 0; spincnt < 10; spincnt++) { |
f7f7bac9 | 1442 | trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait")); |
f8b7fc6b | 1443 | local_bh_disable(); |
f8b7fc6b | 1444 | *statusp = RCU_KTHREAD_RUNNING; |
62ab7072 PM |
1445 | this_cpu_inc(rcu_cpu_kthread_loops); |
1446 | local_irq_disable(); | |
f8b7fc6b PM |
1447 | work = *workp; |
1448 | *workp = 0; | |
62ab7072 | 1449 | local_irq_enable(); |
f8b7fc6b PM |
1450 | if (work) |
1451 | rcu_kthread_do_work(); | |
1452 | local_bh_enable(); | |
62ab7072 | 1453 | if (*workp == 0) { |
f7f7bac9 | 1454 | trace_rcu_utilization(TPS("End CPU kthread@rcu_wait")); |
62ab7072 PM |
1455 | *statusp = RCU_KTHREAD_WAITING; |
1456 | return; | |
f8b7fc6b PM |
1457 | } |
1458 | } | |
62ab7072 | 1459 | *statusp = RCU_KTHREAD_YIELDING; |
f7f7bac9 | 1460 | trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield")); |
62ab7072 | 1461 | schedule_timeout_interruptible(2); |
f7f7bac9 | 1462 | trace_rcu_utilization(TPS("End CPU kthread@rcu_yield")); |
62ab7072 | 1463 | *statusp = RCU_KTHREAD_WAITING; |
f8b7fc6b PM |
1464 | } |
1465 | ||
1466 | /* | |
1467 | * Set the per-rcu_node kthread's affinity to cover all CPUs that are | |
1468 | * served by the rcu_node in question. The CPU hotplug lock is still | |
1469 | * held, so the value of rnp->qsmaskinit will be stable. | |
1470 | * | |
1471 | * We don't include outgoingcpu in the affinity set, use -1 if there is | |
1472 | * no outgoing CPU. If there are no CPUs left in the affinity set, | |
1473 | * this function allows the kthread to execute on any CPU. | |
1474 | */ | |
5d01bbd1 | 1475 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
f8b7fc6b | 1476 | { |
5d01bbd1 TG |
1477 | struct task_struct *t = rnp->boost_kthread_task; |
1478 | unsigned long mask = rnp->qsmaskinit; | |
f8b7fc6b PM |
1479 | cpumask_var_t cm; |
1480 | int cpu; | |
f8b7fc6b | 1481 | |
5d01bbd1 | 1482 | if (!t) |
f8b7fc6b | 1483 | return; |
5d01bbd1 | 1484 | if (!zalloc_cpumask_var(&cm, GFP_KERNEL)) |
f8b7fc6b | 1485 | return; |
f8b7fc6b PM |
1486 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) |
1487 | if ((mask & 0x1) && cpu != outgoingcpu) | |
1488 | cpumask_set_cpu(cpu, cm); | |
1489 | if (cpumask_weight(cm) == 0) { | |
1490 | cpumask_setall(cm); | |
1491 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) | |
1492 | cpumask_clear_cpu(cpu, cm); | |
1493 | WARN_ON_ONCE(cpumask_weight(cm) == 0); | |
1494 | } | |
5d01bbd1 | 1495 | set_cpus_allowed_ptr(t, cm); |
f8b7fc6b PM |
1496 | free_cpumask_var(cm); |
1497 | } | |
1498 | ||
62ab7072 PM |
1499 | static struct smp_hotplug_thread rcu_cpu_thread_spec = { |
1500 | .store = &rcu_cpu_kthread_task, | |
1501 | .thread_should_run = rcu_cpu_kthread_should_run, | |
1502 | .thread_fn = rcu_cpu_kthread, | |
1503 | .thread_comm = "rcuc/%u", | |
1504 | .setup = rcu_cpu_kthread_setup, | |
1505 | .park = rcu_cpu_kthread_park, | |
1506 | }; | |
f8b7fc6b PM |
1507 | |
1508 | /* | |
1509 | * Spawn all kthreads -- called as soon as the scheduler is running. | |
1510 | */ | |
1511 | static int __init rcu_spawn_kthreads(void) | |
1512 | { | |
f8b7fc6b | 1513 | struct rcu_node *rnp; |
5d01bbd1 | 1514 | int cpu; |
f8b7fc6b | 1515 | |
b0d30417 | 1516 | rcu_scheduler_fully_active = 1; |
62ab7072 | 1517 | for_each_possible_cpu(cpu) |
f8b7fc6b | 1518 | per_cpu(rcu_cpu_has_work, cpu) = 0; |
62ab7072 | 1519 | BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec)); |
f8b7fc6b | 1520 | rnp = rcu_get_root(rcu_state); |
5d01bbd1 | 1521 | (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); |
f8b7fc6b PM |
1522 | if (NUM_RCU_NODES > 1) { |
1523 | rcu_for_each_leaf_node(rcu_state, rnp) | |
5d01bbd1 | 1524 | (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); |
f8b7fc6b PM |
1525 | } |
1526 | return 0; | |
1527 | } | |
1528 | early_initcall(rcu_spawn_kthreads); | |
1529 | ||
49fb4c62 | 1530 | static void rcu_prepare_kthreads(int cpu) |
f8b7fc6b PM |
1531 | { |
1532 | struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu); | |
1533 | struct rcu_node *rnp = rdp->mynode; | |
1534 | ||
1535 | /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ | |
62ab7072 | 1536 | if (rcu_scheduler_fully_active) |
5d01bbd1 | 1537 | (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); |
f8b7fc6b PM |
1538 | } |
1539 | ||
27f4d280 PM |
1540 | #else /* #ifdef CONFIG_RCU_BOOST */ |
1541 | ||
1217ed1b | 1542 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
27f4d280 | 1543 | { |
1217ed1b | 1544 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 PM |
1545 | } |
1546 | ||
a46e0899 | 1547 | static void invoke_rcu_callbacks_kthread(void) |
27f4d280 | 1548 | { |
a46e0899 | 1549 | WARN_ON_ONCE(1); |
27f4d280 PM |
1550 | } |
1551 | ||
dff1672d PM |
1552 | static bool rcu_is_callbacks_kthread(void) |
1553 | { | |
1554 | return false; | |
1555 | } | |
1556 | ||
27f4d280 PM |
1557 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) |
1558 | { | |
1559 | } | |
1560 | ||
5d01bbd1 | 1561 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
f8b7fc6b PM |
1562 | { |
1563 | } | |
1564 | ||
b0d30417 PM |
1565 | static int __init rcu_scheduler_really_started(void) |
1566 | { | |
1567 | rcu_scheduler_fully_active = 1; | |
1568 | return 0; | |
1569 | } | |
1570 | early_initcall(rcu_scheduler_really_started); | |
1571 | ||
49fb4c62 | 1572 | static void rcu_prepare_kthreads(int cpu) |
f8b7fc6b PM |
1573 | { |
1574 | } | |
1575 | ||
27f4d280 PM |
1576 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ |
1577 | ||
8bd93a2c PM |
1578 | #if !defined(CONFIG_RCU_FAST_NO_HZ) |
1579 | ||
1580 | /* | |
1581 | * Check to see if any future RCU-related work will need to be done | |
1582 | * by the current CPU, even if none need be done immediately, returning | |
1583 | * 1 if so. This function is part of the RCU implementation; it is -not- | |
1584 | * an exported member of the RCU API. | |
1585 | * | |
7cb92499 PM |
1586 | * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs |
1587 | * any flavor of RCU. | |
8bd93a2c | 1588 | */ |
ffa83fb5 | 1589 | #ifndef CONFIG_RCU_NOCB_CPU_ALL |
aa9b1630 | 1590 | int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) |
8bd93a2c | 1591 | { |
aa9b1630 | 1592 | *delta_jiffies = ULONG_MAX; |
c0f4dfd4 | 1593 | return rcu_cpu_has_callbacks(cpu, NULL); |
7cb92499 | 1594 | } |
ffa83fb5 | 1595 | #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ |
7cb92499 PM |
1596 | |
1597 | /* | |
1598 | * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up | |
1599 | * after it. | |
1600 | */ | |
1601 | static void rcu_cleanup_after_idle(int cpu) | |
1602 | { | |
1603 | } | |
1604 | ||
aea1b35e | 1605 | /* |
a858af28 | 1606 | * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n, |
aea1b35e PM |
1607 | * is nothing. |
1608 | */ | |
1609 | static void rcu_prepare_for_idle(int cpu) | |
1610 | { | |
1611 | } | |
1612 | ||
c57afe80 PM |
1613 | /* |
1614 | * Don't bother keeping a running count of the number of RCU callbacks | |
1615 | * posted because CONFIG_RCU_FAST_NO_HZ=n. | |
1616 | */ | |
1617 | static void rcu_idle_count_callbacks_posted(void) | |
1618 | { | |
1619 | } | |
1620 | ||
8bd93a2c PM |
1621 | #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
1622 | ||
f23f7fa1 PM |
1623 | /* |
1624 | * This code is invoked when a CPU goes idle, at which point we want | |
1625 | * to have the CPU do everything required for RCU so that it can enter | |
1626 | * the energy-efficient dyntick-idle mode. This is handled by a | |
1627 | * state machine implemented by rcu_prepare_for_idle() below. | |
1628 | * | |
1629 | * The following three proprocessor symbols control this state machine: | |
1630 | * | |
f23f7fa1 PM |
1631 | * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted |
1632 | * to sleep in dyntick-idle mode with RCU callbacks pending. This | |
1633 | * is sized to be roughly one RCU grace period. Those energy-efficiency | |
1634 | * benchmarkers who might otherwise be tempted to set this to a large | |
1635 | * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your | |
1636 | * system. And if you are -that- concerned about energy efficiency, | |
1637 | * just power the system down and be done with it! | |
778d250a PM |
1638 | * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is |
1639 | * permitted to sleep in dyntick-idle mode with only lazy RCU | |
1640 | * callbacks pending. Setting this too high can OOM your system. | |
f23f7fa1 PM |
1641 | * |
1642 | * The values below work well in practice. If future workloads require | |
1643 | * adjustment, they can be converted into kernel config parameters, though | |
1644 | * making the state machine smarter might be a better option. | |
1645 | */ | |
e84c48ae | 1646 | #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */ |
778d250a | 1647 | #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */ |
f23f7fa1 | 1648 | |
5e44ce35 PM |
1649 | static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY; |
1650 | module_param(rcu_idle_gp_delay, int, 0644); | |
1651 | static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY; | |
1652 | module_param(rcu_idle_lazy_gp_delay, int, 0644); | |
486e2593 | 1653 | |
d689fe22 | 1654 | extern int tick_nohz_active; |
486e2593 PM |
1655 | |
1656 | /* | |
c229828c PM |
1657 | * Try to advance callbacks for all flavors of RCU on the current CPU, but |
1658 | * only if it has been awhile since the last time we did so. Afterwards, | |
1659 | * if there are any callbacks ready for immediate invocation, return true. | |
486e2593 | 1660 | */ |
f1f399d1 | 1661 | static bool __maybe_unused rcu_try_advance_all_cbs(void) |
486e2593 | 1662 | { |
c0f4dfd4 PM |
1663 | bool cbs_ready = false; |
1664 | struct rcu_data *rdp; | |
c229828c | 1665 | struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
c0f4dfd4 PM |
1666 | struct rcu_node *rnp; |
1667 | struct rcu_state *rsp; | |
486e2593 | 1668 | |
c229828c PM |
1669 | /* Exit early if we advanced recently. */ |
1670 | if (jiffies == rdtp->last_advance_all) | |
1671 | return 0; | |
1672 | rdtp->last_advance_all = jiffies; | |
1673 | ||
c0f4dfd4 PM |
1674 | for_each_rcu_flavor(rsp) { |
1675 | rdp = this_cpu_ptr(rsp->rda); | |
1676 | rnp = rdp->mynode; | |
486e2593 | 1677 | |
c0f4dfd4 PM |
1678 | /* |
1679 | * Don't bother checking unless a grace period has | |
1680 | * completed since we last checked and there are | |
1681 | * callbacks not yet ready to invoke. | |
1682 | */ | |
1683 | if (rdp->completed != rnp->completed && | |
1684 | rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL]) | |
470716fc | 1685 | note_gp_changes(rsp, rdp); |
486e2593 | 1686 | |
c0f4dfd4 PM |
1687 | if (cpu_has_callbacks_ready_to_invoke(rdp)) |
1688 | cbs_ready = true; | |
1689 | } | |
1690 | return cbs_ready; | |
486e2593 PM |
1691 | } |
1692 | ||
aa9b1630 | 1693 | /* |
c0f4dfd4 PM |
1694 | * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready |
1695 | * to invoke. If the CPU has callbacks, try to advance them. Tell the | |
1696 | * caller to set the timeout based on whether or not there are non-lazy | |
1697 | * callbacks. | |
aa9b1630 | 1698 | * |
c0f4dfd4 | 1699 | * The caller must have disabled interrupts. |
aa9b1630 | 1700 | */ |
ffa83fb5 | 1701 | #ifndef CONFIG_RCU_NOCB_CPU_ALL |
c0f4dfd4 | 1702 | int rcu_needs_cpu(int cpu, unsigned long *dj) |
aa9b1630 PM |
1703 | { |
1704 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); | |
1705 | ||
c0f4dfd4 PM |
1706 | /* Snapshot to detect later posting of non-lazy callback. */ |
1707 | rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; | |
1708 | ||
aa9b1630 | 1709 | /* If no callbacks, RCU doesn't need the CPU. */ |
c0f4dfd4 PM |
1710 | if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) { |
1711 | *dj = ULONG_MAX; | |
aa9b1630 PM |
1712 | return 0; |
1713 | } | |
c0f4dfd4 PM |
1714 | |
1715 | /* Attempt to advance callbacks. */ | |
1716 | if (rcu_try_advance_all_cbs()) { | |
1717 | /* Some ready to invoke, so initiate later invocation. */ | |
1718 | invoke_rcu_core(); | |
aa9b1630 PM |
1719 | return 1; |
1720 | } | |
c0f4dfd4 PM |
1721 | rdtp->last_accelerate = jiffies; |
1722 | ||
1723 | /* Request timer delay depending on laziness, and round. */ | |
6faf7283 | 1724 | if (!rdtp->all_lazy) { |
c0f4dfd4 PM |
1725 | *dj = round_up(rcu_idle_gp_delay + jiffies, |
1726 | rcu_idle_gp_delay) - jiffies; | |
e84c48ae | 1727 | } else { |
c0f4dfd4 | 1728 | *dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies; |
e84c48ae | 1729 | } |
aa9b1630 PM |
1730 | return 0; |
1731 | } | |
ffa83fb5 | 1732 | #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ |
aa9b1630 | 1733 | |
21e52e15 | 1734 | /* |
c0f4dfd4 PM |
1735 | * Prepare a CPU for idle from an RCU perspective. The first major task |
1736 | * is to sense whether nohz mode has been enabled or disabled via sysfs. | |
1737 | * The second major task is to check to see if a non-lazy callback has | |
1738 | * arrived at a CPU that previously had only lazy callbacks. The third | |
1739 | * major task is to accelerate (that is, assign grace-period numbers to) | |
1740 | * any recently arrived callbacks. | |
aea1b35e PM |
1741 | * |
1742 | * The caller must have disabled interrupts. | |
8bd93a2c | 1743 | */ |
aea1b35e | 1744 | static void rcu_prepare_for_idle(int cpu) |
8bd93a2c | 1745 | { |
f1f399d1 | 1746 | #ifndef CONFIG_RCU_NOCB_CPU_ALL |
c0f4dfd4 | 1747 | struct rcu_data *rdp; |
5955f7ee | 1748 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
c0f4dfd4 PM |
1749 | struct rcu_node *rnp; |
1750 | struct rcu_state *rsp; | |
9d2ad243 PM |
1751 | int tne; |
1752 | ||
1753 | /* Handle nohz enablement switches conservatively. */ | |
d689fe22 | 1754 | tne = ACCESS_ONCE(tick_nohz_active); |
9d2ad243 | 1755 | if (tne != rdtp->tick_nohz_enabled_snap) { |
c0f4dfd4 | 1756 | if (rcu_cpu_has_callbacks(cpu, NULL)) |
9d2ad243 PM |
1757 | invoke_rcu_core(); /* force nohz to see update. */ |
1758 | rdtp->tick_nohz_enabled_snap = tne; | |
1759 | return; | |
1760 | } | |
1761 | if (!tne) | |
1762 | return; | |
f511fc62 | 1763 | |
c0f4dfd4 | 1764 | /* If this is a no-CBs CPU, no callbacks, just return. */ |
534c97b0 | 1765 | if (rcu_is_nocb_cpu(cpu)) |
9a0c6fef | 1766 | return; |
9a0c6fef | 1767 | |
c57afe80 | 1768 | /* |
c0f4dfd4 PM |
1769 | * If a non-lazy callback arrived at a CPU having only lazy |
1770 | * callbacks, invoke RCU core for the side-effect of recalculating | |
1771 | * idle duration on re-entry to idle. | |
c57afe80 | 1772 | */ |
c0f4dfd4 PM |
1773 | if (rdtp->all_lazy && |
1774 | rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) { | |
c337f8f5 PM |
1775 | rdtp->all_lazy = false; |
1776 | rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; | |
c0f4dfd4 | 1777 | invoke_rcu_core(); |
c57afe80 PM |
1778 | return; |
1779 | } | |
c57afe80 | 1780 | |
3084f2f8 | 1781 | /* |
c0f4dfd4 PM |
1782 | * If we have not yet accelerated this jiffy, accelerate all |
1783 | * callbacks on this CPU. | |
3084f2f8 | 1784 | */ |
c0f4dfd4 | 1785 | if (rdtp->last_accelerate == jiffies) |
aea1b35e | 1786 | return; |
c0f4dfd4 PM |
1787 | rdtp->last_accelerate = jiffies; |
1788 | for_each_rcu_flavor(rsp) { | |
1789 | rdp = per_cpu_ptr(rsp->rda, cpu); | |
1790 | if (!*rdp->nxttail[RCU_DONE_TAIL]) | |
1791 | continue; | |
1792 | rnp = rdp->mynode; | |
1793 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ | |
6303b9c8 | 1794 | smp_mb__after_unlock_lock(); |
c0f4dfd4 PM |
1795 | rcu_accelerate_cbs(rsp, rnp, rdp); |
1796 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ | |
77e38ed3 | 1797 | } |
f1f399d1 | 1798 | #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ |
c0f4dfd4 | 1799 | } |
3084f2f8 | 1800 | |
c0f4dfd4 PM |
1801 | /* |
1802 | * Clean up for exit from idle. Attempt to advance callbacks based on | |
1803 | * any grace periods that elapsed while the CPU was idle, and if any | |
1804 | * callbacks are now ready to invoke, initiate invocation. | |
1805 | */ | |
1806 | static void rcu_cleanup_after_idle(int cpu) | |
1807 | { | |
f1f399d1 | 1808 | #ifndef CONFIG_RCU_NOCB_CPU_ALL |
534c97b0 | 1809 | if (rcu_is_nocb_cpu(cpu)) |
aea1b35e | 1810 | return; |
7a497c96 PM |
1811 | if (rcu_try_advance_all_cbs()) |
1812 | invoke_rcu_core(); | |
f1f399d1 | 1813 | #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ |
8bd93a2c PM |
1814 | } |
1815 | ||
c57afe80 | 1816 | /* |
98248a0e PM |
1817 | * Keep a running count of the number of non-lazy callbacks posted |
1818 | * on this CPU. This running counter (which is never decremented) allows | |
1819 | * rcu_prepare_for_idle() to detect when something out of the idle loop | |
1820 | * posts a callback, even if an equal number of callbacks are invoked. | |
1821 | * Of course, callbacks should only be posted from within a trace event | |
1822 | * designed to be called from idle or from within RCU_NONIDLE(). | |
c57afe80 PM |
1823 | */ |
1824 | static void rcu_idle_count_callbacks_posted(void) | |
1825 | { | |
5955f7ee | 1826 | __this_cpu_add(rcu_dynticks.nonlazy_posted, 1); |
c57afe80 PM |
1827 | } |
1828 | ||
b626c1b6 PM |
1829 | /* |
1830 | * Data for flushing lazy RCU callbacks at OOM time. | |
1831 | */ | |
1832 | static atomic_t oom_callback_count; | |
1833 | static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq); | |
1834 | ||
1835 | /* | |
1836 | * RCU OOM callback -- decrement the outstanding count and deliver the | |
1837 | * wake-up if we are the last one. | |
1838 | */ | |
1839 | static void rcu_oom_callback(struct rcu_head *rhp) | |
1840 | { | |
1841 | if (atomic_dec_and_test(&oom_callback_count)) | |
1842 | wake_up(&oom_callback_wq); | |
1843 | } | |
1844 | ||
1845 | /* | |
1846 | * Post an rcu_oom_notify callback on the current CPU if it has at | |
1847 | * least one lazy callback. This will unnecessarily post callbacks | |
1848 | * to CPUs that already have a non-lazy callback at the end of their | |
1849 | * callback list, but this is an infrequent operation, so accept some | |
1850 | * extra overhead to keep things simple. | |
1851 | */ | |
1852 | static void rcu_oom_notify_cpu(void *unused) | |
1853 | { | |
1854 | struct rcu_state *rsp; | |
1855 | struct rcu_data *rdp; | |
1856 | ||
1857 | for_each_rcu_flavor(rsp) { | |
1858 | rdp = __this_cpu_ptr(rsp->rda); | |
1859 | if (rdp->qlen_lazy != 0) { | |
1860 | atomic_inc(&oom_callback_count); | |
1861 | rsp->call(&rdp->oom_head, rcu_oom_callback); | |
1862 | } | |
1863 | } | |
1864 | } | |
1865 | ||
1866 | /* | |
1867 | * If low on memory, ensure that each CPU has a non-lazy callback. | |
1868 | * This will wake up CPUs that have only lazy callbacks, in turn | |
1869 | * ensuring that they free up the corresponding memory in a timely manner. | |
1870 | * Because an uncertain amount of memory will be freed in some uncertain | |
1871 | * timeframe, we do not claim to have freed anything. | |
1872 | */ | |
1873 | static int rcu_oom_notify(struct notifier_block *self, | |
1874 | unsigned long notused, void *nfreed) | |
1875 | { | |
1876 | int cpu; | |
1877 | ||
1878 | /* Wait for callbacks from earlier instance to complete. */ | |
1879 | wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0); | |
78e4bc34 | 1880 | smp_mb(); /* Ensure callback reuse happens after callback invocation. */ |
b626c1b6 PM |
1881 | |
1882 | /* | |
1883 | * Prevent premature wakeup: ensure that all increments happen | |
1884 | * before there is a chance of the counter reaching zero. | |
1885 | */ | |
1886 | atomic_set(&oom_callback_count, 1); | |
1887 | ||
1888 | get_online_cpus(); | |
1889 | for_each_online_cpu(cpu) { | |
1890 | smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1); | |
1891 | cond_resched(); | |
1892 | } | |
1893 | put_online_cpus(); | |
1894 | ||
1895 | /* Unconditionally decrement: no need to wake ourselves up. */ | |
1896 | atomic_dec(&oom_callback_count); | |
1897 | ||
1898 | return NOTIFY_OK; | |
1899 | } | |
1900 | ||
1901 | static struct notifier_block rcu_oom_nb = { | |
1902 | .notifier_call = rcu_oom_notify | |
1903 | }; | |
1904 | ||
1905 | static int __init rcu_register_oom_notifier(void) | |
1906 | { | |
1907 | register_oom_notifier(&rcu_oom_nb); | |
1908 | return 0; | |
1909 | } | |
1910 | early_initcall(rcu_register_oom_notifier); | |
1911 | ||
8bd93a2c | 1912 | #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
a858af28 PM |
1913 | |
1914 | #ifdef CONFIG_RCU_CPU_STALL_INFO | |
1915 | ||
1916 | #ifdef CONFIG_RCU_FAST_NO_HZ | |
1917 | ||
1918 | static void print_cpu_stall_fast_no_hz(char *cp, int cpu) | |
1919 | { | |
5955f7ee | 1920 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
c0f4dfd4 | 1921 | unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap; |
a858af28 | 1922 | |
c0f4dfd4 PM |
1923 | sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c", |
1924 | rdtp->last_accelerate & 0xffff, jiffies & 0xffff, | |
1925 | ulong2long(nlpd), | |
1926 | rdtp->all_lazy ? 'L' : '.', | |
1927 | rdtp->tick_nohz_enabled_snap ? '.' : 'D'); | |
a858af28 PM |
1928 | } |
1929 | ||
1930 | #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ | |
1931 | ||
1932 | static void print_cpu_stall_fast_no_hz(char *cp, int cpu) | |
1933 | { | |
1c17e4d4 | 1934 | *cp = '\0'; |
a858af28 PM |
1935 | } |
1936 | ||
1937 | #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ | |
1938 | ||
1939 | /* Initiate the stall-info list. */ | |
1940 | static void print_cpu_stall_info_begin(void) | |
1941 | { | |
efc151c3 | 1942 | pr_cont("\n"); |
a858af28 PM |
1943 | } |
1944 | ||
1945 | /* | |
1946 | * Print out diagnostic information for the specified stalled CPU. | |
1947 | * | |
1948 | * If the specified CPU is aware of the current RCU grace period | |
1949 | * (flavor specified by rsp), then print the number of scheduling | |
1950 | * clock interrupts the CPU has taken during the time that it has | |
1951 | * been aware. Otherwise, print the number of RCU grace periods | |
1952 | * that this CPU is ignorant of, for example, "1" if the CPU was | |
1953 | * aware of the previous grace period. | |
1954 | * | |
1955 | * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. | |
1956 | */ | |
1957 | static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) | |
1958 | { | |
1959 | char fast_no_hz[72]; | |
1960 | struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); | |
1961 | struct rcu_dynticks *rdtp = rdp->dynticks; | |
1962 | char *ticks_title; | |
1963 | unsigned long ticks_value; | |
1964 | ||
1965 | if (rsp->gpnum == rdp->gpnum) { | |
1966 | ticks_title = "ticks this GP"; | |
1967 | ticks_value = rdp->ticks_this_gp; | |
1968 | } else { | |
1969 | ticks_title = "GPs behind"; | |
1970 | ticks_value = rsp->gpnum - rdp->gpnum; | |
1971 | } | |
1972 | print_cpu_stall_fast_no_hz(fast_no_hz, cpu); | |
efc151c3 | 1973 | pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n", |
a858af28 PM |
1974 | cpu, ticks_value, ticks_title, |
1975 | atomic_read(&rdtp->dynticks) & 0xfff, | |
1976 | rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting, | |
6231069b | 1977 | rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu), |
a858af28 PM |
1978 | fast_no_hz); |
1979 | } | |
1980 | ||
1981 | /* Terminate the stall-info list. */ | |
1982 | static void print_cpu_stall_info_end(void) | |
1983 | { | |
efc151c3 | 1984 | pr_err("\t"); |
a858af28 PM |
1985 | } |
1986 | ||
1987 | /* Zero ->ticks_this_gp for all flavors of RCU. */ | |
1988 | static void zero_cpu_stall_ticks(struct rcu_data *rdp) | |
1989 | { | |
1990 | rdp->ticks_this_gp = 0; | |
6231069b | 1991 | rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id()); |
a858af28 PM |
1992 | } |
1993 | ||
1994 | /* Increment ->ticks_this_gp for all flavors of RCU. */ | |
1995 | static void increment_cpu_stall_ticks(void) | |
1996 | { | |
115f7a7c PM |
1997 | struct rcu_state *rsp; |
1998 | ||
1999 | for_each_rcu_flavor(rsp) | |
2000 | __this_cpu_ptr(rsp->rda)->ticks_this_gp++; | |
a858af28 PM |
2001 | } |
2002 | ||
2003 | #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ | |
2004 | ||
2005 | static void print_cpu_stall_info_begin(void) | |
2006 | { | |
efc151c3 | 2007 | pr_cont(" {"); |
a858af28 PM |
2008 | } |
2009 | ||
2010 | static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) | |
2011 | { | |
efc151c3 | 2012 | pr_cont(" %d", cpu); |
a858af28 PM |
2013 | } |
2014 | ||
2015 | static void print_cpu_stall_info_end(void) | |
2016 | { | |
efc151c3 | 2017 | pr_cont("} "); |
a858af28 PM |
2018 | } |
2019 | ||
2020 | static void zero_cpu_stall_ticks(struct rcu_data *rdp) | |
2021 | { | |
2022 | } | |
2023 | ||
2024 | static void increment_cpu_stall_ticks(void) | |
2025 | { | |
2026 | } | |
2027 | ||
2028 | #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */ | |
3fbfbf7a PM |
2029 | |
2030 | #ifdef CONFIG_RCU_NOCB_CPU | |
2031 | ||
2032 | /* | |
2033 | * Offload callback processing from the boot-time-specified set of CPUs | |
2034 | * specified by rcu_nocb_mask. For each CPU in the set, there is a | |
2035 | * kthread created that pulls the callbacks from the corresponding CPU, | |
2036 | * waits for a grace period to elapse, and invokes the callbacks. | |
2037 | * The no-CBs CPUs do a wake_up() on their kthread when they insert | |
2038 | * a callback into any empty list, unless the rcu_nocb_poll boot parameter | |
2039 | * has been specified, in which case each kthread actively polls its | |
2040 | * CPU. (Which isn't so great for energy efficiency, but which does | |
2041 | * reduce RCU's overhead on that CPU.) | |
2042 | * | |
2043 | * This is intended to be used in conjunction with Frederic Weisbecker's | |
2044 | * adaptive-idle work, which would seriously reduce OS jitter on CPUs | |
2045 | * running CPU-bound user-mode computations. | |
2046 | * | |
2047 | * Offloading of callback processing could also in theory be used as | |
2048 | * an energy-efficiency measure because CPUs with no RCU callbacks | |
2049 | * queued are more aggressive about entering dyntick-idle mode. | |
2050 | */ | |
2051 | ||
2052 | ||
2053 | /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */ | |
2054 | static int __init rcu_nocb_setup(char *str) | |
2055 | { | |
2056 | alloc_bootmem_cpumask_var(&rcu_nocb_mask); | |
2057 | have_rcu_nocb_mask = true; | |
2058 | cpulist_parse(str, rcu_nocb_mask); | |
2059 | return 1; | |
2060 | } | |
2061 | __setup("rcu_nocbs=", rcu_nocb_setup); | |
2062 | ||
1b0048a4 PG |
2063 | static int __init parse_rcu_nocb_poll(char *arg) |
2064 | { | |
2065 | rcu_nocb_poll = 1; | |
2066 | return 0; | |
2067 | } | |
2068 | early_param("rcu_nocb_poll", parse_rcu_nocb_poll); | |
2069 | ||
34ed6246 | 2070 | /* |
dae6e64d PM |
2071 | * Do any no-CBs CPUs need another grace period? |
2072 | * | |
2073 | * Interrupts must be disabled. If the caller does not hold the root | |
2074 | * rnp_node structure's ->lock, the results are advisory only. | |
2075 | */ | |
2076 | static int rcu_nocb_needs_gp(struct rcu_state *rsp) | |
2077 | { | |
2078 | struct rcu_node *rnp = rcu_get_root(rsp); | |
2079 | ||
8b425aa8 | 2080 | return rnp->need_future_gp[(ACCESS_ONCE(rnp->completed) + 1) & 0x1]; |
dae6e64d PM |
2081 | } |
2082 | ||
2083 | /* | |
0446be48 PM |
2084 | * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended |
2085 | * grace period. | |
dae6e64d | 2086 | */ |
0446be48 | 2087 | static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) |
dae6e64d | 2088 | { |
0446be48 | 2089 | wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]); |
dae6e64d PM |
2090 | } |
2091 | ||
2092 | /* | |
8b425aa8 | 2093 | * Set the root rcu_node structure's ->need_future_gp field |
dae6e64d PM |
2094 | * based on the sum of those of all rcu_node structures. This does |
2095 | * double-count the root rcu_node structure's requests, but this | |
2096 | * is necessary to handle the possibility of a rcu_nocb_kthread() | |
2097 | * having awakened during the time that the rcu_node structures | |
2098 | * were being updated for the end of the previous grace period. | |
34ed6246 | 2099 | */ |
dae6e64d PM |
2100 | static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) |
2101 | { | |
8b425aa8 | 2102 | rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq; |
dae6e64d PM |
2103 | } |
2104 | ||
2105 | static void rcu_init_one_nocb(struct rcu_node *rnp) | |
34ed6246 | 2106 | { |
dae6e64d PM |
2107 | init_waitqueue_head(&rnp->nocb_gp_wq[0]); |
2108 | init_waitqueue_head(&rnp->nocb_gp_wq[1]); | |
34ed6246 PM |
2109 | } |
2110 | ||
2f33b512 | 2111 | #ifndef CONFIG_RCU_NOCB_CPU_ALL |
3fbfbf7a | 2112 | /* Is the specified CPU a no-CPUs CPU? */ |
d1e43fa5 | 2113 | bool rcu_is_nocb_cpu(int cpu) |
3fbfbf7a PM |
2114 | { |
2115 | if (have_rcu_nocb_mask) | |
2116 | return cpumask_test_cpu(cpu, rcu_nocb_mask); | |
2117 | return false; | |
2118 | } | |
2f33b512 | 2119 | #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ |
3fbfbf7a PM |
2120 | |
2121 | /* | |
2122 | * Enqueue the specified string of rcu_head structures onto the specified | |
2123 | * CPU's no-CBs lists. The CPU is specified by rdp, the head of the | |
2124 | * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy | |
2125 | * counts are supplied by rhcount and rhcount_lazy. | |
2126 | * | |
2127 | * If warranted, also wake up the kthread servicing this CPUs queues. | |
2128 | */ | |
2129 | static void __call_rcu_nocb_enqueue(struct rcu_data *rdp, | |
2130 | struct rcu_head *rhp, | |
2131 | struct rcu_head **rhtp, | |
96d3fd0d PM |
2132 | int rhcount, int rhcount_lazy, |
2133 | unsigned long flags) | |
3fbfbf7a PM |
2134 | { |
2135 | int len; | |
2136 | struct rcu_head **old_rhpp; | |
2137 | struct task_struct *t; | |
2138 | ||
2139 | /* Enqueue the callback on the nocb list and update counts. */ | |
2140 | old_rhpp = xchg(&rdp->nocb_tail, rhtp); | |
2141 | ACCESS_ONCE(*old_rhpp) = rhp; | |
2142 | atomic_long_add(rhcount, &rdp->nocb_q_count); | |
2143 | atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy); | |
2144 | ||
2145 | /* If we are not being polled and there is a kthread, awaken it ... */ | |
2146 | t = ACCESS_ONCE(rdp->nocb_kthread); | |
25e03a74 | 2147 | if (rcu_nocb_poll || !t) { |
9261dd0d PM |
2148 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
2149 | TPS("WakeNotPoll")); | |
3fbfbf7a | 2150 | return; |
9261dd0d | 2151 | } |
3fbfbf7a PM |
2152 | len = atomic_long_read(&rdp->nocb_q_count); |
2153 | if (old_rhpp == &rdp->nocb_head) { | |
96d3fd0d PM |
2154 | if (!irqs_disabled_flags(flags)) { |
2155 | wake_up(&rdp->nocb_wq); /* ... if queue was empty ... */ | |
2156 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, | |
2157 | TPS("WakeEmpty")); | |
2158 | } else { | |
2159 | rdp->nocb_defer_wakeup = true; | |
2160 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, | |
2161 | TPS("WakeEmptyIsDeferred")); | |
2162 | } | |
3fbfbf7a PM |
2163 | rdp->qlen_last_fqs_check = 0; |
2164 | } else if (len > rdp->qlen_last_fqs_check + qhimark) { | |
2165 | wake_up_process(t); /* ... or if many callbacks queued. */ | |
2166 | rdp->qlen_last_fqs_check = LONG_MAX / 2; | |
9261dd0d PM |
2167 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf")); |
2168 | } else { | |
2169 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot")); | |
3fbfbf7a PM |
2170 | } |
2171 | return; | |
2172 | } | |
2173 | ||
2174 | /* | |
2175 | * This is a helper for __call_rcu(), which invokes this when the normal | |
2176 | * callback queue is inoperable. If this is not a no-CBs CPU, this | |
2177 | * function returns failure back to __call_rcu(), which can complain | |
2178 | * appropriately. | |
2179 | * | |
2180 | * Otherwise, this function queues the callback where the corresponding | |
2181 | * "rcuo" kthread can find it. | |
2182 | */ | |
2183 | static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, | |
96d3fd0d | 2184 | bool lazy, unsigned long flags) |
3fbfbf7a PM |
2185 | { |
2186 | ||
d1e43fa5 | 2187 | if (!rcu_is_nocb_cpu(rdp->cpu)) |
3fbfbf7a | 2188 | return 0; |
96d3fd0d | 2189 | __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags); |
21e7a608 PM |
2190 | if (__is_kfree_rcu_offset((unsigned long)rhp->func)) |
2191 | trace_rcu_kfree_callback(rdp->rsp->name, rhp, | |
2192 | (unsigned long)rhp->func, | |
756cbf6b PM |
2193 | -atomic_long_read(&rdp->nocb_q_count_lazy), |
2194 | -atomic_long_read(&rdp->nocb_q_count)); | |
21e7a608 PM |
2195 | else |
2196 | trace_rcu_callback(rdp->rsp->name, rhp, | |
756cbf6b PM |
2197 | -atomic_long_read(&rdp->nocb_q_count_lazy), |
2198 | -atomic_long_read(&rdp->nocb_q_count)); | |
3fbfbf7a PM |
2199 | return 1; |
2200 | } | |
2201 | ||
2202 | /* | |
2203 | * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is | |
2204 | * not a no-CBs CPU. | |
2205 | */ | |
2206 | static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, | |
96d3fd0d PM |
2207 | struct rcu_data *rdp, |
2208 | unsigned long flags) | |
3fbfbf7a PM |
2209 | { |
2210 | long ql = rsp->qlen; | |
2211 | long qll = rsp->qlen_lazy; | |
2212 | ||
2213 | /* If this is not a no-CBs CPU, tell the caller to do it the old way. */ | |
d1e43fa5 | 2214 | if (!rcu_is_nocb_cpu(smp_processor_id())) |
3fbfbf7a PM |
2215 | return 0; |
2216 | rsp->qlen = 0; | |
2217 | rsp->qlen_lazy = 0; | |
2218 | ||
2219 | /* First, enqueue the donelist, if any. This preserves CB ordering. */ | |
2220 | if (rsp->orphan_donelist != NULL) { | |
2221 | __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist, | |
96d3fd0d | 2222 | rsp->orphan_donetail, ql, qll, flags); |
3fbfbf7a PM |
2223 | ql = qll = 0; |
2224 | rsp->orphan_donelist = NULL; | |
2225 | rsp->orphan_donetail = &rsp->orphan_donelist; | |
2226 | } | |
2227 | if (rsp->orphan_nxtlist != NULL) { | |
2228 | __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist, | |
96d3fd0d | 2229 | rsp->orphan_nxttail, ql, qll, flags); |
3fbfbf7a PM |
2230 | ql = qll = 0; |
2231 | rsp->orphan_nxtlist = NULL; | |
2232 | rsp->orphan_nxttail = &rsp->orphan_nxtlist; | |
2233 | } | |
2234 | return 1; | |
2235 | } | |
2236 | ||
2237 | /* | |
34ed6246 PM |
2238 | * If necessary, kick off a new grace period, and either way wait |
2239 | * for a subsequent grace period to complete. | |
3fbfbf7a | 2240 | */ |
34ed6246 | 2241 | static void rcu_nocb_wait_gp(struct rcu_data *rdp) |
3fbfbf7a | 2242 | { |
34ed6246 | 2243 | unsigned long c; |
dae6e64d | 2244 | bool d; |
34ed6246 | 2245 | unsigned long flags; |
34ed6246 PM |
2246 | struct rcu_node *rnp = rdp->mynode; |
2247 | ||
2248 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
6303b9c8 | 2249 | smp_mb__after_unlock_lock(); |
0446be48 PM |
2250 | c = rcu_start_future_gp(rnp, rdp); |
2251 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
3fbfbf7a PM |
2252 | |
2253 | /* | |
34ed6246 PM |
2254 | * Wait for the grace period. Do so interruptibly to avoid messing |
2255 | * up the load average. | |
3fbfbf7a | 2256 | */ |
f7f7bac9 | 2257 | trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait")); |
34ed6246 | 2258 | for (;;) { |
dae6e64d PM |
2259 | wait_event_interruptible( |
2260 | rnp->nocb_gp_wq[c & 0x1], | |
2261 | (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c))); | |
2262 | if (likely(d)) | |
34ed6246 | 2263 | break; |
dae6e64d | 2264 | flush_signals(current); |
f7f7bac9 | 2265 | trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait")); |
34ed6246 | 2266 | } |
f7f7bac9 | 2267 | trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait")); |
34ed6246 | 2268 | smp_mb(); /* Ensure that CB invocation happens after GP end. */ |
3fbfbf7a PM |
2269 | } |
2270 | ||
2271 | /* | |
2272 | * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes | |
2273 | * callbacks queued by the corresponding no-CBs CPU. | |
2274 | */ | |
2275 | static int rcu_nocb_kthread(void *arg) | |
2276 | { | |
2277 | int c, cl; | |
69a79bb1 | 2278 | bool firsttime = 1; |
3fbfbf7a PM |
2279 | struct rcu_head *list; |
2280 | struct rcu_head *next; | |
2281 | struct rcu_head **tail; | |
2282 | struct rcu_data *rdp = arg; | |
2283 | ||
2284 | /* Each pass through this loop invokes one batch of callbacks */ | |
2285 | for (;;) { | |
2286 | /* If not polling, wait for next batch of callbacks. */ | |
69a79bb1 PM |
2287 | if (!rcu_nocb_poll) { |
2288 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, | |
2289 | TPS("Sleep")); | |
353af9c9 | 2290 | wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head); |
78e4bc34 | 2291 | /* Memory barrier provide by xchg() below. */ |
69a79bb1 PM |
2292 | } else if (firsttime) { |
2293 | firsttime = 0; | |
2294 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, | |
2295 | TPS("Poll")); | |
2296 | } | |
3fbfbf7a PM |
2297 | list = ACCESS_ONCE(rdp->nocb_head); |
2298 | if (!list) { | |
9261dd0d PM |
2299 | if (!rcu_nocb_poll) |
2300 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, | |
2301 | TPS("WokeEmpty")); | |
3fbfbf7a | 2302 | schedule_timeout_interruptible(1); |
353af9c9 | 2303 | flush_signals(current); |
3fbfbf7a PM |
2304 | continue; |
2305 | } | |
69a79bb1 | 2306 | firsttime = 1; |
9261dd0d PM |
2307 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
2308 | TPS("WokeNonEmpty")); | |
3fbfbf7a PM |
2309 | |
2310 | /* | |
2311 | * Extract queued callbacks, update counts, and wait | |
2312 | * for a grace period to elapse. | |
2313 | */ | |
2314 | ACCESS_ONCE(rdp->nocb_head) = NULL; | |
2315 | tail = xchg(&rdp->nocb_tail, &rdp->nocb_head); | |
2316 | c = atomic_long_xchg(&rdp->nocb_q_count, 0); | |
2317 | cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0); | |
2318 | ACCESS_ONCE(rdp->nocb_p_count) += c; | |
2319 | ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl; | |
34ed6246 | 2320 | rcu_nocb_wait_gp(rdp); |
3fbfbf7a PM |
2321 | |
2322 | /* Each pass through the following loop invokes a callback. */ | |
2323 | trace_rcu_batch_start(rdp->rsp->name, cl, c, -1); | |
2324 | c = cl = 0; | |
2325 | while (list) { | |
2326 | next = list->next; | |
2327 | /* Wait for enqueuing to complete, if needed. */ | |
2328 | while (next == NULL && &list->next != tail) { | |
69a79bb1 PM |
2329 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
2330 | TPS("WaitQueue")); | |
3fbfbf7a | 2331 | schedule_timeout_interruptible(1); |
69a79bb1 PM |
2332 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
2333 | TPS("WokeQueue")); | |
3fbfbf7a PM |
2334 | next = list->next; |
2335 | } | |
2336 | debug_rcu_head_unqueue(list); | |
2337 | local_bh_disable(); | |
2338 | if (__rcu_reclaim(rdp->rsp->name, list)) | |
2339 | cl++; | |
2340 | c++; | |
2341 | local_bh_enable(); | |
2342 | list = next; | |
2343 | } | |
2344 | trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1); | |
2345 | ACCESS_ONCE(rdp->nocb_p_count) -= c; | |
2346 | ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl; | |
c635a4e1 | 2347 | rdp->n_nocbs_invoked += c; |
3fbfbf7a PM |
2348 | } |
2349 | return 0; | |
2350 | } | |
2351 | ||
96d3fd0d PM |
2352 | /* Is a deferred wakeup of rcu_nocb_kthread() required? */ |
2353 | static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) | |
2354 | { | |
2355 | return ACCESS_ONCE(rdp->nocb_defer_wakeup); | |
2356 | } | |
2357 | ||
2358 | /* Do a deferred wakeup of rcu_nocb_kthread(). */ | |
2359 | static void do_nocb_deferred_wakeup(struct rcu_data *rdp) | |
2360 | { | |
2361 | if (!rcu_nocb_need_deferred_wakeup(rdp)) | |
2362 | return; | |
2363 | ACCESS_ONCE(rdp->nocb_defer_wakeup) = false; | |
2364 | wake_up(&rdp->nocb_wq); | |
2365 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWakeEmpty")); | |
2366 | } | |
2367 | ||
3fbfbf7a PM |
2368 | /* Initialize per-rcu_data variables for no-CBs CPUs. */ |
2369 | static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) | |
2370 | { | |
2371 | rdp->nocb_tail = &rdp->nocb_head; | |
2372 | init_waitqueue_head(&rdp->nocb_wq); | |
2373 | } | |
2374 | ||
2375 | /* Create a kthread for each RCU flavor for each no-CBs CPU. */ | |
2376 | static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp) | |
2377 | { | |
2378 | int cpu; | |
2379 | struct rcu_data *rdp; | |
2380 | struct task_struct *t; | |
2381 | ||
2382 | if (rcu_nocb_mask == NULL) | |
2383 | return; | |
2384 | for_each_cpu(cpu, rcu_nocb_mask) { | |
2385 | rdp = per_cpu_ptr(rsp->rda, cpu); | |
a4889858 PM |
2386 | t = kthread_run(rcu_nocb_kthread, rdp, |
2387 | "rcuo%c/%d", rsp->abbr, cpu); | |
3fbfbf7a PM |
2388 | BUG_ON(IS_ERR(t)); |
2389 | ACCESS_ONCE(rdp->nocb_kthread) = t; | |
2390 | } | |
2391 | } | |
2392 | ||
2393 | /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */ | |
34ed6246 | 2394 | static bool init_nocb_callback_list(struct rcu_data *rdp) |
3fbfbf7a PM |
2395 | { |
2396 | if (rcu_nocb_mask == NULL || | |
2397 | !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask)) | |
34ed6246 | 2398 | return false; |
3fbfbf7a | 2399 | rdp->nxttail[RCU_NEXT_TAIL] = NULL; |
34ed6246 | 2400 | return true; |
3fbfbf7a PM |
2401 | } |
2402 | ||
34ed6246 PM |
2403 | #else /* #ifdef CONFIG_RCU_NOCB_CPU */ |
2404 | ||
dae6e64d PM |
2405 | static int rcu_nocb_needs_gp(struct rcu_state *rsp) |
2406 | { | |
2407 | return 0; | |
3fbfbf7a PM |
2408 | } |
2409 | ||
0446be48 | 2410 | static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) |
3fbfbf7a | 2411 | { |
3fbfbf7a PM |
2412 | } |
2413 | ||
dae6e64d PM |
2414 | static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) |
2415 | { | |
2416 | } | |
2417 | ||
2418 | static void rcu_init_one_nocb(struct rcu_node *rnp) | |
2419 | { | |
2420 | } | |
3fbfbf7a | 2421 | |
3fbfbf7a | 2422 | static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, |
96d3fd0d | 2423 | bool lazy, unsigned long flags) |
3fbfbf7a PM |
2424 | { |
2425 | return 0; | |
2426 | } | |
2427 | ||
2428 | static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, | |
96d3fd0d PM |
2429 | struct rcu_data *rdp, |
2430 | unsigned long flags) | |
3fbfbf7a PM |
2431 | { |
2432 | return 0; | |
2433 | } | |
2434 | ||
3fbfbf7a PM |
2435 | static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) |
2436 | { | |
2437 | } | |
2438 | ||
96d3fd0d PM |
2439 | static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) |
2440 | { | |
2441 | return false; | |
2442 | } | |
2443 | ||
2444 | static void do_nocb_deferred_wakeup(struct rcu_data *rdp) | |
2445 | { | |
2446 | } | |
2447 | ||
3fbfbf7a PM |
2448 | static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp) |
2449 | { | |
2450 | } | |
2451 | ||
34ed6246 | 2452 | static bool init_nocb_callback_list(struct rcu_data *rdp) |
3fbfbf7a | 2453 | { |
34ed6246 | 2454 | return false; |
3fbfbf7a PM |
2455 | } |
2456 | ||
2457 | #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ | |
65d798f0 PM |
2458 | |
2459 | /* | |
2460 | * An adaptive-ticks CPU can potentially execute in kernel mode for an | |
2461 | * arbitrarily long period of time with the scheduling-clock tick turned | |
2462 | * off. RCU will be paying attention to this CPU because it is in the | |
2463 | * kernel, but the CPU cannot be guaranteed to be executing the RCU state | |
2464 | * machine because the scheduling-clock tick has been disabled. Therefore, | |
2465 | * if an adaptive-ticks CPU is failing to respond to the current grace | |
2466 | * period and has not be idle from an RCU perspective, kick it. | |
2467 | */ | |
2468 | static void rcu_kick_nohz_cpu(int cpu) | |
2469 | { | |
2470 | #ifdef CONFIG_NO_HZ_FULL | |
2471 | if (tick_nohz_full_cpu(cpu)) | |
2472 | smp_send_reschedule(cpu); | |
2473 | #endif /* #ifdef CONFIG_NO_HZ_FULL */ | |
2474 | } | |
2333210b PM |
2475 | |
2476 | ||
2477 | #ifdef CONFIG_NO_HZ_FULL_SYSIDLE | |
2478 | ||
d4bd54fb PM |
2479 | /* |
2480 | * Define RCU flavor that holds sysidle state. This needs to be the | |
2481 | * most active flavor of RCU. | |
2482 | */ | |
2483 | #ifdef CONFIG_PREEMPT_RCU | |
0edd1b17 | 2484 | static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state; |
d4bd54fb | 2485 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
0edd1b17 | 2486 | static struct rcu_state *rcu_sysidle_state = &rcu_sched_state; |
d4bd54fb PM |
2487 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
2488 | ||
0edd1b17 | 2489 | static int full_sysidle_state; /* Current system-idle state. */ |
d4bd54fb PM |
2490 | #define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */ |
2491 | #define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */ | |
2492 | #define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */ | |
2493 | #define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */ | |
2494 | #define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */ | |
2495 | ||
eb348b89 PM |
2496 | /* |
2497 | * Invoked to note exit from irq or task transition to idle. Note that | |
2498 | * usermode execution does -not- count as idle here! After all, we want | |
2499 | * to detect full-system idle states, not RCU quiescent states and grace | |
2500 | * periods. The caller must have disabled interrupts. | |
2501 | */ | |
2502 | static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq) | |
2503 | { | |
2504 | unsigned long j; | |
2505 | ||
2506 | /* Adjust nesting, check for fully idle. */ | |
2507 | if (irq) { | |
2508 | rdtp->dynticks_idle_nesting--; | |
2509 | WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0); | |
2510 | if (rdtp->dynticks_idle_nesting != 0) | |
2511 | return; /* Still not fully idle. */ | |
2512 | } else { | |
2513 | if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) == | |
2514 | DYNTICK_TASK_NEST_VALUE) { | |
2515 | rdtp->dynticks_idle_nesting = 0; | |
2516 | } else { | |
2517 | rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE; | |
2518 | WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0); | |
2519 | return; /* Still not fully idle. */ | |
2520 | } | |
2521 | } | |
2522 | ||
2523 | /* Record start of fully idle period. */ | |
2524 | j = jiffies; | |
2525 | ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j; | |
2526 | smp_mb__before_atomic_inc(); | |
2527 | atomic_inc(&rdtp->dynticks_idle); | |
2528 | smp_mb__after_atomic_inc(); | |
2529 | WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1); | |
2530 | } | |
2531 | ||
0edd1b17 PM |
2532 | /* |
2533 | * Unconditionally force exit from full system-idle state. This is | |
2534 | * invoked when a normal CPU exits idle, but must be called separately | |
2535 | * for the timekeeping CPU (tick_do_timer_cpu). The reason for this | |
2536 | * is that the timekeeping CPU is permitted to take scheduling-clock | |
2537 | * interrupts while the system is in system-idle state, and of course | |
2538 | * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock | |
2539 | * interrupt from any other type of interrupt. | |
2540 | */ | |
2541 | void rcu_sysidle_force_exit(void) | |
2542 | { | |
2543 | int oldstate = ACCESS_ONCE(full_sysidle_state); | |
2544 | int newoldstate; | |
2545 | ||
2546 | /* | |
2547 | * Each pass through the following loop attempts to exit full | |
2548 | * system-idle state. If contention proves to be a problem, | |
2549 | * a trylock-based contention tree could be used here. | |
2550 | */ | |
2551 | while (oldstate > RCU_SYSIDLE_SHORT) { | |
2552 | newoldstate = cmpxchg(&full_sysidle_state, | |
2553 | oldstate, RCU_SYSIDLE_NOT); | |
2554 | if (oldstate == newoldstate && | |
2555 | oldstate == RCU_SYSIDLE_FULL_NOTED) { | |
2556 | rcu_kick_nohz_cpu(tick_do_timer_cpu); | |
2557 | return; /* We cleared it, done! */ | |
2558 | } | |
2559 | oldstate = newoldstate; | |
2560 | } | |
2561 | smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */ | |
2562 | } | |
2563 | ||
eb348b89 PM |
2564 | /* |
2565 | * Invoked to note entry to irq or task transition from idle. Note that | |
2566 | * usermode execution does -not- count as idle here! The caller must | |
2567 | * have disabled interrupts. | |
2568 | */ | |
2569 | static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq) | |
2570 | { | |
2571 | /* Adjust nesting, check for already non-idle. */ | |
2572 | if (irq) { | |
2573 | rdtp->dynticks_idle_nesting++; | |
2574 | WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0); | |
2575 | if (rdtp->dynticks_idle_nesting != 1) | |
2576 | return; /* Already non-idle. */ | |
2577 | } else { | |
2578 | /* | |
2579 | * Allow for irq misnesting. Yes, it really is possible | |
2580 | * to enter an irq handler then never leave it, and maybe | |
2581 | * also vice versa. Handle both possibilities. | |
2582 | */ | |
2583 | if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) { | |
2584 | rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE; | |
2585 | WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0); | |
2586 | return; /* Already non-idle. */ | |
2587 | } else { | |
2588 | rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE; | |
2589 | } | |
2590 | } | |
2591 | ||
2592 | /* Record end of idle period. */ | |
2593 | smp_mb__before_atomic_inc(); | |
2594 | atomic_inc(&rdtp->dynticks_idle); | |
2595 | smp_mb__after_atomic_inc(); | |
2596 | WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1)); | |
0edd1b17 PM |
2597 | |
2598 | /* | |
2599 | * If we are the timekeeping CPU, we are permitted to be non-idle | |
2600 | * during a system-idle state. This must be the case, because | |
2601 | * the timekeeping CPU has to take scheduling-clock interrupts | |
2602 | * during the time that the system is transitioning to full | |
2603 | * system-idle state. This means that the timekeeping CPU must | |
2604 | * invoke rcu_sysidle_force_exit() directly if it does anything | |
2605 | * more than take a scheduling-clock interrupt. | |
2606 | */ | |
2607 | if (smp_processor_id() == tick_do_timer_cpu) | |
2608 | return; | |
2609 | ||
2610 | /* Update system-idle state: We are clearly no longer fully idle! */ | |
2611 | rcu_sysidle_force_exit(); | |
2612 | } | |
2613 | ||
2614 | /* | |
2615 | * Check to see if the current CPU is idle. Note that usermode execution | |
2616 | * does not count as idle. The caller must have disabled interrupts. | |
2617 | */ | |
2618 | static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, | |
2619 | unsigned long *maxj) | |
2620 | { | |
2621 | int cur; | |
2622 | unsigned long j; | |
2623 | struct rcu_dynticks *rdtp = rdp->dynticks; | |
2624 | ||
2625 | /* | |
2626 | * If some other CPU has already reported non-idle, if this is | |
2627 | * not the flavor of RCU that tracks sysidle state, or if this | |
2628 | * is an offline or the timekeeping CPU, nothing to do. | |
2629 | */ | |
2630 | if (!*isidle || rdp->rsp != rcu_sysidle_state || | |
2631 | cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu) | |
2632 | return; | |
eb75767b PM |
2633 | if (rcu_gp_in_progress(rdp->rsp)) |
2634 | WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu); | |
0edd1b17 PM |
2635 | |
2636 | /* Pick up current idle and NMI-nesting counter and check. */ | |
2637 | cur = atomic_read(&rdtp->dynticks_idle); | |
2638 | if (cur & 0x1) { | |
2639 | *isidle = false; /* We are not idle! */ | |
2640 | return; | |
2641 | } | |
2642 | smp_mb(); /* Read counters before timestamps. */ | |
2643 | ||
2644 | /* Pick up timestamps. */ | |
2645 | j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies); | |
2646 | /* If this CPU entered idle more recently, update maxj timestamp. */ | |
2647 | if (ULONG_CMP_LT(*maxj, j)) | |
2648 | *maxj = j; | |
2649 | } | |
2650 | ||
2651 | /* | |
2652 | * Is this the flavor of RCU that is handling full-system idle? | |
2653 | */ | |
2654 | static bool is_sysidle_rcu_state(struct rcu_state *rsp) | |
2655 | { | |
2656 | return rsp == rcu_sysidle_state; | |
2657 | } | |
2658 | ||
eb75767b PM |
2659 | /* |
2660 | * Bind the grace-period kthread for the sysidle flavor of RCU to the | |
2661 | * timekeeping CPU. | |
2662 | */ | |
2663 | static void rcu_bind_gp_kthread(void) | |
2664 | { | |
2665 | int cpu = ACCESS_ONCE(tick_do_timer_cpu); | |
2666 | ||
2667 | if (cpu < 0 || cpu >= nr_cpu_ids) | |
2668 | return; | |
2669 | if (raw_smp_processor_id() != cpu) | |
2670 | set_cpus_allowed_ptr(current, cpumask_of(cpu)); | |
2671 | } | |
2672 | ||
0edd1b17 PM |
2673 | /* |
2674 | * Return a delay in jiffies based on the number of CPUs, rcu_node | |
2675 | * leaf fanout, and jiffies tick rate. The idea is to allow larger | |
2676 | * systems more time to transition to full-idle state in order to | |
2677 | * avoid the cache thrashing that otherwise occur on the state variable. | |
2678 | * Really small systems (less than a couple of tens of CPUs) should | |
2679 | * instead use a single global atomically incremented counter, and later | |
2680 | * versions of this will automatically reconfigure themselves accordingly. | |
2681 | */ | |
2682 | static unsigned long rcu_sysidle_delay(void) | |
2683 | { | |
2684 | if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) | |
2685 | return 0; | |
2686 | return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000); | |
2687 | } | |
2688 | ||
2689 | /* | |
2690 | * Advance the full-system-idle state. This is invoked when all of | |
2691 | * the non-timekeeping CPUs are idle. | |
2692 | */ | |
2693 | static void rcu_sysidle(unsigned long j) | |
2694 | { | |
2695 | /* Check the current state. */ | |
2696 | switch (ACCESS_ONCE(full_sysidle_state)) { | |
2697 | case RCU_SYSIDLE_NOT: | |
2698 | ||
2699 | /* First time all are idle, so note a short idle period. */ | |
2700 | ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT; | |
2701 | break; | |
2702 | ||
2703 | case RCU_SYSIDLE_SHORT: | |
2704 | ||
2705 | /* | |
2706 | * Idle for a bit, time to advance to next state? | |
2707 | * cmpxchg failure means race with non-idle, let them win. | |
2708 | */ | |
2709 | if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay())) | |
2710 | (void)cmpxchg(&full_sysidle_state, | |
2711 | RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG); | |
2712 | break; | |
2713 | ||
2714 | case RCU_SYSIDLE_LONG: | |
2715 | ||
2716 | /* | |
2717 | * Do an additional check pass before advancing to full. | |
2718 | * cmpxchg failure means race with non-idle, let them win. | |
2719 | */ | |
2720 | if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay())) | |
2721 | (void)cmpxchg(&full_sysidle_state, | |
2722 | RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL); | |
2723 | break; | |
2724 | ||
2725 | default: | |
2726 | break; | |
2727 | } | |
2728 | } | |
2729 | ||
2730 | /* | |
2731 | * Found a non-idle non-timekeeping CPU, so kick the system-idle state | |
2732 | * back to the beginning. | |
2733 | */ | |
2734 | static void rcu_sysidle_cancel(void) | |
2735 | { | |
2736 | smp_mb(); | |
2737 | ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT; | |
2738 | } | |
2739 | ||
2740 | /* | |
2741 | * Update the sysidle state based on the results of a force-quiescent-state | |
2742 | * scan of the CPUs' dyntick-idle state. | |
2743 | */ | |
2744 | static void rcu_sysidle_report(struct rcu_state *rsp, int isidle, | |
2745 | unsigned long maxj, bool gpkt) | |
2746 | { | |
2747 | if (rsp != rcu_sysidle_state) | |
2748 | return; /* Wrong flavor, ignore. */ | |
2749 | if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) | |
2750 | return; /* Running state machine from timekeeping CPU. */ | |
2751 | if (isidle) | |
2752 | rcu_sysidle(maxj); /* More idle! */ | |
2753 | else | |
2754 | rcu_sysidle_cancel(); /* Idle is over. */ | |
2755 | } | |
2756 | ||
2757 | /* | |
2758 | * Wrapper for rcu_sysidle_report() when called from the grace-period | |
2759 | * kthread's context. | |
2760 | */ | |
2761 | static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, | |
2762 | unsigned long maxj) | |
2763 | { | |
2764 | rcu_sysidle_report(rsp, isidle, maxj, true); | |
2765 | } | |
2766 | ||
2767 | /* Callback and function for forcing an RCU grace period. */ | |
2768 | struct rcu_sysidle_head { | |
2769 | struct rcu_head rh; | |
2770 | int inuse; | |
2771 | }; | |
2772 | ||
2773 | static void rcu_sysidle_cb(struct rcu_head *rhp) | |
2774 | { | |
2775 | struct rcu_sysidle_head *rshp; | |
2776 | ||
2777 | /* | |
2778 | * The following memory barrier is needed to replace the | |
2779 | * memory barriers that would normally be in the memory | |
2780 | * allocator. | |
2781 | */ | |
2782 | smp_mb(); /* grace period precedes setting inuse. */ | |
2783 | ||
2784 | rshp = container_of(rhp, struct rcu_sysidle_head, rh); | |
2785 | ACCESS_ONCE(rshp->inuse) = 0; | |
2786 | } | |
2787 | ||
2788 | /* | |
2789 | * Check to see if the system is fully idle, other than the timekeeping CPU. | |
2790 | * The caller must have disabled interrupts. | |
2791 | */ | |
2792 | bool rcu_sys_is_idle(void) | |
2793 | { | |
2794 | static struct rcu_sysidle_head rsh; | |
2795 | int rss = ACCESS_ONCE(full_sysidle_state); | |
2796 | ||
2797 | if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu)) | |
2798 | return false; | |
2799 | ||
2800 | /* Handle small-system case by doing a full scan of CPUs. */ | |
2801 | if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) { | |
2802 | int oldrss = rss - 1; | |
2803 | ||
2804 | /* | |
2805 | * One pass to advance to each state up to _FULL. | |
2806 | * Give up if any pass fails to advance the state. | |
2807 | */ | |
2808 | while (rss < RCU_SYSIDLE_FULL && oldrss < rss) { | |
2809 | int cpu; | |
2810 | bool isidle = true; | |
2811 | unsigned long maxj = jiffies - ULONG_MAX / 4; | |
2812 | struct rcu_data *rdp; | |
2813 | ||
2814 | /* Scan all the CPUs looking for nonidle CPUs. */ | |
2815 | for_each_possible_cpu(cpu) { | |
2816 | rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu); | |
2817 | rcu_sysidle_check_cpu(rdp, &isidle, &maxj); | |
2818 | if (!isidle) | |
2819 | break; | |
2820 | } | |
2821 | rcu_sysidle_report(rcu_sysidle_state, | |
2822 | isidle, maxj, false); | |
2823 | oldrss = rss; | |
2824 | rss = ACCESS_ONCE(full_sysidle_state); | |
2825 | } | |
2826 | } | |
2827 | ||
2828 | /* If this is the first observation of an idle period, record it. */ | |
2829 | if (rss == RCU_SYSIDLE_FULL) { | |
2830 | rss = cmpxchg(&full_sysidle_state, | |
2831 | RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED); | |
2832 | return rss == RCU_SYSIDLE_FULL; | |
2833 | } | |
2834 | ||
2835 | smp_mb(); /* ensure rss load happens before later caller actions. */ | |
2836 | ||
2837 | /* If already fully idle, tell the caller (in case of races). */ | |
2838 | if (rss == RCU_SYSIDLE_FULL_NOTED) | |
2839 | return true; | |
2840 | ||
2841 | /* | |
2842 | * If we aren't there yet, and a grace period is not in flight, | |
2843 | * initiate a grace period. Either way, tell the caller that | |
2844 | * we are not there yet. We use an xchg() rather than an assignment | |
2845 | * to make up for the memory barriers that would otherwise be | |
2846 | * provided by the memory allocator. | |
2847 | */ | |
2848 | if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL && | |
2849 | !rcu_gp_in_progress(rcu_sysidle_state) && | |
2850 | !rsh.inuse && xchg(&rsh.inuse, 1) == 0) | |
2851 | call_rcu(&rsh.rh, rcu_sysidle_cb); | |
2852 | return false; | |
eb348b89 PM |
2853 | } |
2854 | ||
2333210b PM |
2855 | /* |
2856 | * Initialize dynticks sysidle state for CPUs coming online. | |
2857 | */ | |
2858 | static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp) | |
2859 | { | |
2860 | rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE; | |
2861 | } | |
2862 | ||
2863 | #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ | |
2864 | ||
eb348b89 PM |
2865 | static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq) |
2866 | { | |
2867 | } | |
2868 | ||
2869 | static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq) | |
2870 | { | |
2871 | } | |
2872 | ||
0edd1b17 PM |
2873 | static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, |
2874 | unsigned long *maxj) | |
2875 | { | |
2876 | } | |
2877 | ||
2878 | static bool is_sysidle_rcu_state(struct rcu_state *rsp) | |
2879 | { | |
2880 | return false; | |
2881 | } | |
2882 | ||
eb75767b PM |
2883 | static void rcu_bind_gp_kthread(void) |
2884 | { | |
2885 | } | |
2886 | ||
0edd1b17 PM |
2887 | static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, |
2888 | unsigned long maxj) | |
2889 | { | |
2890 | } | |
2891 | ||
2333210b PM |
2892 | static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp) |
2893 | { | |
2894 | } | |
2895 | ||
2896 | #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ | |
a096932f PM |
2897 | |
2898 | /* | |
2899 | * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the | |
2900 | * grace-period kthread will do force_quiescent_state() processing? | |
2901 | * The idea is to avoid waking up RCU core processing on such a | |
2902 | * CPU unless the grace period has extended for too long. | |
2903 | * | |
2904 | * This code relies on the fact that all NO_HZ_FULL CPUs are also | |
52e2bb95 | 2905 | * CONFIG_RCU_NOCB_CPU CPUs. |
a096932f PM |
2906 | */ |
2907 | static bool rcu_nohz_full_cpu(struct rcu_state *rsp) | |
2908 | { | |
2909 | #ifdef CONFIG_NO_HZ_FULL | |
2910 | if (tick_nohz_full_cpu(smp_processor_id()) && | |
2911 | (!rcu_gp_in_progress(rsp) || | |
2912 | ULONG_CMP_LT(jiffies, ACCESS_ONCE(rsp->gp_start) + HZ))) | |
2913 | return 1; | |
2914 | #endif /* #ifdef CONFIG_NO_HZ_FULL */ | |
2915 | return 0; | |
2916 | } |