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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 | |
17 | * along with this program; if not, write to the Free Software | |
18 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. | |
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> |
f41d911f | 31 | |
5b61b0ba MG |
32 | #define RCU_KTHREAD_PRIO 1 |
33 | ||
34 | #ifdef CONFIG_RCU_BOOST | |
35 | #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO | |
36 | #else | |
37 | #define RCU_BOOST_PRIO RCU_KTHREAD_PRIO | |
38 | #endif | |
39 | ||
3fbfbf7a PM |
40 | #ifdef CONFIG_RCU_NOCB_CPU |
41 | static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */ | |
42 | static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */ | |
1b0048a4 | 43 | static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */ |
3fbfbf7a PM |
44 | static char __initdata nocb_buf[NR_CPUS * 5]; |
45 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ | |
46 | ||
26845c28 PM |
47 | /* |
48 | * Check the RCU kernel configuration parameters and print informative | |
49 | * messages about anything out of the ordinary. If you like #ifdef, you | |
50 | * will love this function. | |
51 | */ | |
52 | static void __init rcu_bootup_announce_oddness(void) | |
53 | { | |
54 | #ifdef CONFIG_RCU_TRACE | |
55 | printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n"); | |
56 | #endif | |
57 | #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32) | |
58 | printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n", | |
59 | CONFIG_RCU_FANOUT); | |
60 | #endif | |
61 | #ifdef CONFIG_RCU_FANOUT_EXACT | |
62 | printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n"); | |
63 | #endif | |
64 | #ifdef CONFIG_RCU_FAST_NO_HZ | |
65 | printk(KERN_INFO | |
66 | "\tRCU dyntick-idle grace-period acceleration is enabled.\n"); | |
67 | #endif | |
68 | #ifdef CONFIG_PROVE_RCU | |
69 | printk(KERN_INFO "\tRCU lockdep checking is enabled.\n"); | |
70 | #endif | |
71 | #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE | |
72 | printk(KERN_INFO "\tRCU torture testing starts during boot.\n"); | |
73 | #endif | |
81a294c4 | 74 | #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE) |
a858af28 PM |
75 | printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n"); |
76 | #endif | |
77 | #if defined(CONFIG_RCU_CPU_STALL_INFO) | |
78 | printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n"); | |
26845c28 PM |
79 | #endif |
80 | #if NUM_RCU_LVL_4 != 0 | |
cc5df65b | 81 | printk(KERN_INFO "\tFour-level hierarchy is enabled.\n"); |
26845c28 | 82 | #endif |
f885b7f2 PM |
83 | if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF) |
84 | printk(KERN_INFO "\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf); | |
cca6f393 PM |
85 | if (nr_cpu_ids != NR_CPUS) |
86 | printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids); | |
3fbfbf7a PM |
87 | #ifdef CONFIG_RCU_NOCB_CPU |
88 | if (have_rcu_nocb_mask) { | |
89 | if (cpumask_test_cpu(0, rcu_nocb_mask)) { | |
90 | cpumask_clear_cpu(0, rcu_nocb_mask); | |
91 | pr_info("\tCPU 0: illegal no-CBs CPU (cleared).\n"); | |
92 | } | |
93 | cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask); | |
94 | pr_info("\tExperimental no-CBs CPUs: %s.\n", nocb_buf); | |
95 | if (rcu_nocb_poll) | |
96 | pr_info("\tExperimental polled no-CBs CPUs.\n"); | |
97 | } | |
98 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ | |
26845c28 PM |
99 | } |
100 | ||
f41d911f PM |
101 | #ifdef CONFIG_TREE_PREEMPT_RCU |
102 | ||
037b64ed PM |
103 | struct rcu_state rcu_preempt_state = |
104 | RCU_STATE_INITIALIZER(rcu_preempt, call_rcu); | |
f41d911f | 105 | DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data); |
27f4d280 | 106 | static struct rcu_state *rcu_state = &rcu_preempt_state; |
f41d911f | 107 | |
d9a3da06 PM |
108 | static int rcu_preempted_readers_exp(struct rcu_node *rnp); |
109 | ||
f41d911f PM |
110 | /* |
111 | * Tell them what RCU they are running. | |
112 | */ | |
0e0fc1c2 | 113 | static void __init rcu_bootup_announce(void) |
f41d911f | 114 | { |
6cc68793 | 115 | printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n"); |
26845c28 | 116 | rcu_bootup_announce_oddness(); |
f41d911f PM |
117 | } |
118 | ||
119 | /* | |
120 | * Return the number of RCU-preempt batches processed thus far | |
121 | * for debug and statistics. | |
122 | */ | |
123 | long rcu_batches_completed_preempt(void) | |
124 | { | |
125 | return rcu_preempt_state.completed; | |
126 | } | |
127 | EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt); | |
128 | ||
129 | /* | |
130 | * Return the number of RCU batches processed thus far for debug & stats. | |
131 | */ | |
132 | long rcu_batches_completed(void) | |
133 | { | |
134 | return rcu_batches_completed_preempt(); | |
135 | } | |
136 | EXPORT_SYMBOL_GPL(rcu_batches_completed); | |
137 | ||
bf66f18e PM |
138 | /* |
139 | * Force a quiescent state for preemptible RCU. | |
140 | */ | |
141 | void rcu_force_quiescent_state(void) | |
142 | { | |
4cdfc175 | 143 | force_quiescent_state(&rcu_preempt_state); |
bf66f18e PM |
144 | } |
145 | EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); | |
146 | ||
f41d911f | 147 | /* |
6cc68793 | 148 | * Record a preemptible-RCU quiescent state for the specified CPU. Note |
f41d911f PM |
149 | * that this just means that the task currently running on the CPU is |
150 | * not in a quiescent state. There might be any number of tasks blocked | |
151 | * while in an RCU read-side critical section. | |
25502a6c PM |
152 | * |
153 | * Unlike the other rcu_*_qs() functions, callers to this function | |
154 | * must disable irqs in order to protect the assignment to | |
155 | * ->rcu_read_unlock_special. | |
f41d911f | 156 | */ |
c3422bea | 157 | static void rcu_preempt_qs(int cpu) |
f41d911f PM |
158 | { |
159 | struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); | |
25502a6c | 160 | |
e4cc1f22 | 161 | if (rdp->passed_quiesce == 0) |
d4c08f2a | 162 | trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs"); |
e4cc1f22 | 163 | rdp->passed_quiesce = 1; |
25502a6c | 164 | current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; |
f41d911f PM |
165 | } |
166 | ||
167 | /* | |
c3422bea PM |
168 | * We have entered the scheduler, and the current task might soon be |
169 | * context-switched away from. If this task is in an RCU read-side | |
170 | * critical section, we will no longer be able to rely on the CPU to | |
12f5f524 PM |
171 | * record that fact, so we enqueue the task on the blkd_tasks list. |
172 | * The task will dequeue itself when it exits the outermost enclosing | |
173 | * RCU read-side critical section. Therefore, the current grace period | |
174 | * cannot be permitted to complete until the blkd_tasks list entries | |
175 | * predating the current grace period drain, in other words, until | |
176 | * rnp->gp_tasks becomes NULL. | |
c3422bea PM |
177 | * |
178 | * Caller must disable preemption. | |
f41d911f | 179 | */ |
cba6d0d6 | 180 | static void rcu_preempt_note_context_switch(int cpu) |
f41d911f PM |
181 | { |
182 | struct task_struct *t = current; | |
c3422bea | 183 | unsigned long flags; |
f41d911f PM |
184 | struct rcu_data *rdp; |
185 | struct rcu_node *rnp; | |
186 | ||
10f39bb1 | 187 | if (t->rcu_read_lock_nesting > 0 && |
f41d911f PM |
188 | (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { |
189 | ||
190 | /* Possibly blocking in an RCU read-side critical section. */ | |
cba6d0d6 | 191 | rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu); |
f41d911f | 192 | rnp = rdp->mynode; |
1304afb2 | 193 | raw_spin_lock_irqsave(&rnp->lock, flags); |
f41d911f | 194 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; |
86848966 | 195 | t->rcu_blocked_node = rnp; |
f41d911f PM |
196 | |
197 | /* | |
198 | * If this CPU has already checked in, then this task | |
199 | * will hold up the next grace period rather than the | |
200 | * current grace period. Queue the task accordingly. | |
201 | * If the task is queued for the current grace period | |
202 | * (i.e., this CPU has not yet passed through a quiescent | |
203 | * state for the current grace period), then as long | |
204 | * as that task remains queued, the current grace period | |
12f5f524 PM |
205 | * cannot end. Note that there is some uncertainty as |
206 | * to exactly when the current grace period started. | |
207 | * We take a conservative approach, which can result | |
208 | * in unnecessarily waiting on tasks that started very | |
209 | * slightly after the current grace period began. C'est | |
210 | * la vie!!! | |
b0e165c0 PM |
211 | * |
212 | * But first, note that the current CPU must still be | |
213 | * on line! | |
f41d911f | 214 | */ |
b0e165c0 | 215 | WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0); |
e7d8842e | 216 | WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); |
12f5f524 PM |
217 | if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) { |
218 | list_add(&t->rcu_node_entry, rnp->gp_tasks->prev); | |
219 | rnp->gp_tasks = &t->rcu_node_entry; | |
27f4d280 PM |
220 | #ifdef CONFIG_RCU_BOOST |
221 | if (rnp->boost_tasks != NULL) | |
222 | rnp->boost_tasks = rnp->gp_tasks; | |
223 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
12f5f524 PM |
224 | } else { |
225 | list_add(&t->rcu_node_entry, &rnp->blkd_tasks); | |
226 | if (rnp->qsmask & rdp->grpmask) | |
227 | rnp->gp_tasks = &t->rcu_node_entry; | |
228 | } | |
d4c08f2a PM |
229 | trace_rcu_preempt_task(rdp->rsp->name, |
230 | t->pid, | |
231 | (rnp->qsmask & rdp->grpmask) | |
232 | ? rnp->gpnum | |
233 | : rnp->gpnum + 1); | |
1304afb2 | 234 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
10f39bb1 PM |
235 | } else if (t->rcu_read_lock_nesting < 0 && |
236 | t->rcu_read_unlock_special) { | |
237 | ||
238 | /* | |
239 | * Complete exit from RCU read-side critical section on | |
240 | * behalf of preempted instance of __rcu_read_unlock(). | |
241 | */ | |
242 | rcu_read_unlock_special(t); | |
f41d911f PM |
243 | } |
244 | ||
245 | /* | |
246 | * Either we were not in an RCU read-side critical section to | |
247 | * begin with, or we have now recorded that critical section | |
248 | * globally. Either way, we can now note a quiescent state | |
249 | * for this CPU. Again, if we were in an RCU read-side critical | |
250 | * section, and if that critical section was blocking the current | |
251 | * grace period, then the fact that the task has been enqueued | |
252 | * means that we continue to block the current grace period. | |
253 | */ | |
e7d8842e | 254 | local_irq_save(flags); |
cba6d0d6 | 255 | rcu_preempt_qs(cpu); |
e7d8842e | 256 | local_irq_restore(flags); |
f41d911f PM |
257 | } |
258 | ||
fc2219d4 PM |
259 | /* |
260 | * Check for preempted RCU readers blocking the current grace period | |
261 | * for the specified rcu_node structure. If the caller needs a reliable | |
262 | * answer, it must hold the rcu_node's ->lock. | |
263 | */ | |
27f4d280 | 264 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
fc2219d4 | 265 | { |
12f5f524 | 266 | return rnp->gp_tasks != NULL; |
fc2219d4 PM |
267 | } |
268 | ||
b668c9cf PM |
269 | /* |
270 | * Record a quiescent state for all tasks that were previously queued | |
271 | * on the specified rcu_node structure and that were blocking the current | |
272 | * RCU grace period. The caller must hold the specified rnp->lock with | |
273 | * irqs disabled, and this lock is released upon return, but irqs remain | |
274 | * disabled. | |
275 | */ | |
d3f6bad3 | 276 | static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
b668c9cf PM |
277 | __releases(rnp->lock) |
278 | { | |
279 | unsigned long mask; | |
280 | struct rcu_node *rnp_p; | |
281 | ||
27f4d280 | 282 | if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { |
1304afb2 | 283 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b668c9cf PM |
284 | return; /* Still need more quiescent states! */ |
285 | } | |
286 | ||
287 | rnp_p = rnp->parent; | |
288 | if (rnp_p == NULL) { | |
289 | /* | |
290 | * Either there is only one rcu_node in the tree, | |
291 | * or tasks were kicked up to root rcu_node due to | |
292 | * CPUs going offline. | |
293 | */ | |
d3f6bad3 | 294 | rcu_report_qs_rsp(&rcu_preempt_state, flags); |
b668c9cf PM |
295 | return; |
296 | } | |
297 | ||
298 | /* Report up the rest of the hierarchy. */ | |
299 | mask = rnp->grpmask; | |
1304afb2 PM |
300 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
301 | raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */ | |
d3f6bad3 | 302 | rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags); |
b668c9cf PM |
303 | } |
304 | ||
12f5f524 PM |
305 | /* |
306 | * Advance a ->blkd_tasks-list pointer to the next entry, instead | |
307 | * returning NULL if at the end of the list. | |
308 | */ | |
309 | static struct list_head *rcu_next_node_entry(struct task_struct *t, | |
310 | struct rcu_node *rnp) | |
311 | { | |
312 | struct list_head *np; | |
313 | ||
314 | np = t->rcu_node_entry.next; | |
315 | if (np == &rnp->blkd_tasks) | |
316 | np = NULL; | |
317 | return np; | |
318 | } | |
319 | ||
b668c9cf PM |
320 | /* |
321 | * Handle special cases during rcu_read_unlock(), such as needing to | |
322 | * notify RCU core processing or task having blocked during the RCU | |
323 | * read-side critical section. | |
324 | */ | |
2a3fa843 | 325 | void rcu_read_unlock_special(struct task_struct *t) |
f41d911f PM |
326 | { |
327 | int empty; | |
d9a3da06 | 328 | int empty_exp; |
389abd48 | 329 | int empty_exp_now; |
f41d911f | 330 | unsigned long flags; |
12f5f524 | 331 | struct list_head *np; |
82e78d80 PM |
332 | #ifdef CONFIG_RCU_BOOST |
333 | struct rt_mutex *rbmp = NULL; | |
334 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
f41d911f PM |
335 | struct rcu_node *rnp; |
336 | int special; | |
337 | ||
338 | /* NMI handlers cannot block and cannot safely manipulate state. */ | |
339 | if (in_nmi()) | |
340 | return; | |
341 | ||
342 | local_irq_save(flags); | |
343 | ||
344 | /* | |
345 | * If RCU core is waiting for this CPU to exit critical section, | |
346 | * let it know that we have done so. | |
347 | */ | |
348 | special = t->rcu_read_unlock_special; | |
349 | if (special & RCU_READ_UNLOCK_NEED_QS) { | |
c3422bea | 350 | rcu_preempt_qs(smp_processor_id()); |
f41d911f PM |
351 | } |
352 | ||
353 | /* Hardware IRQ handlers cannot block. */ | |
ec433f0c | 354 | if (in_irq() || in_serving_softirq()) { |
f41d911f PM |
355 | local_irq_restore(flags); |
356 | return; | |
357 | } | |
358 | ||
359 | /* Clean up if blocked during RCU read-side critical section. */ | |
360 | if (special & RCU_READ_UNLOCK_BLOCKED) { | |
361 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; | |
362 | ||
dd5d19ba PM |
363 | /* |
364 | * Remove this task from the list it blocked on. The | |
365 | * task can migrate while we acquire the lock, but at | |
366 | * most one time. So at most two passes through loop. | |
367 | */ | |
368 | for (;;) { | |
86848966 | 369 | rnp = t->rcu_blocked_node; |
1304afb2 | 370 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
86848966 | 371 | if (rnp == t->rcu_blocked_node) |
dd5d19ba | 372 | break; |
1304afb2 | 373 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
dd5d19ba | 374 | } |
27f4d280 | 375 | empty = !rcu_preempt_blocked_readers_cgp(rnp); |
d9a3da06 PM |
376 | empty_exp = !rcu_preempted_readers_exp(rnp); |
377 | smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ | |
12f5f524 | 378 | np = rcu_next_node_entry(t, rnp); |
f41d911f | 379 | list_del_init(&t->rcu_node_entry); |
82e78d80 | 380 | t->rcu_blocked_node = NULL; |
d4c08f2a PM |
381 | trace_rcu_unlock_preempted_task("rcu_preempt", |
382 | rnp->gpnum, t->pid); | |
12f5f524 PM |
383 | if (&t->rcu_node_entry == rnp->gp_tasks) |
384 | rnp->gp_tasks = np; | |
385 | if (&t->rcu_node_entry == rnp->exp_tasks) | |
386 | rnp->exp_tasks = np; | |
27f4d280 PM |
387 | #ifdef CONFIG_RCU_BOOST |
388 | if (&t->rcu_node_entry == rnp->boost_tasks) | |
389 | rnp->boost_tasks = np; | |
82e78d80 PM |
390 | /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */ |
391 | if (t->rcu_boost_mutex) { | |
392 | rbmp = t->rcu_boost_mutex; | |
393 | t->rcu_boost_mutex = NULL; | |
7765be2f | 394 | } |
27f4d280 | 395 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
f41d911f PM |
396 | |
397 | /* | |
398 | * If this was the last task on the current list, and if | |
399 | * we aren't waiting on any CPUs, report the quiescent state. | |
389abd48 PM |
400 | * Note that rcu_report_unblock_qs_rnp() releases rnp->lock, |
401 | * so we must take a snapshot of the expedited state. | |
f41d911f | 402 | */ |
389abd48 | 403 | empty_exp_now = !rcu_preempted_readers_exp(rnp); |
d4c08f2a PM |
404 | if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) { |
405 | trace_rcu_quiescent_state_report("preempt_rcu", | |
406 | rnp->gpnum, | |
407 | 0, rnp->qsmask, | |
408 | rnp->level, | |
409 | rnp->grplo, | |
410 | rnp->grphi, | |
411 | !!rnp->gp_tasks); | |
d3f6bad3 | 412 | rcu_report_unblock_qs_rnp(rnp, flags); |
c701d5d9 | 413 | } else { |
d4c08f2a | 414 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
c701d5d9 | 415 | } |
d9a3da06 | 416 | |
27f4d280 PM |
417 | #ifdef CONFIG_RCU_BOOST |
418 | /* Unboost if we were boosted. */ | |
82e78d80 PM |
419 | if (rbmp) |
420 | rt_mutex_unlock(rbmp); | |
27f4d280 PM |
421 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
422 | ||
d9a3da06 PM |
423 | /* |
424 | * If this was the last task on the expedited lists, | |
425 | * then we need to report up the rcu_node hierarchy. | |
426 | */ | |
389abd48 | 427 | if (!empty_exp && empty_exp_now) |
b40d293e | 428 | rcu_report_exp_rnp(&rcu_preempt_state, rnp, true); |
b668c9cf PM |
429 | } else { |
430 | local_irq_restore(flags); | |
f41d911f | 431 | } |
f41d911f PM |
432 | } |
433 | ||
1ed509a2 PM |
434 | #ifdef CONFIG_RCU_CPU_STALL_VERBOSE |
435 | ||
436 | /* | |
437 | * Dump detailed information for all tasks blocking the current RCU | |
438 | * grace period on the specified rcu_node structure. | |
439 | */ | |
440 | static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) | |
441 | { | |
442 | unsigned long flags; | |
1ed509a2 PM |
443 | struct task_struct *t; |
444 | ||
12f5f524 | 445 | raw_spin_lock_irqsave(&rnp->lock, flags); |
5fd4dc06 PM |
446 | if (!rcu_preempt_blocked_readers_cgp(rnp)) { |
447 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
448 | return; | |
449 | } | |
12f5f524 PM |
450 | t = list_entry(rnp->gp_tasks, |
451 | struct task_struct, rcu_node_entry); | |
452 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) | |
453 | sched_show_task(t); | |
454 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
1ed509a2 PM |
455 | } |
456 | ||
457 | /* | |
458 | * Dump detailed information for all tasks blocking the current RCU | |
459 | * grace period. | |
460 | */ | |
461 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
462 | { | |
463 | struct rcu_node *rnp = rcu_get_root(rsp); | |
464 | ||
465 | rcu_print_detail_task_stall_rnp(rnp); | |
466 | rcu_for_each_leaf_node(rsp, rnp) | |
467 | rcu_print_detail_task_stall_rnp(rnp); | |
468 | } | |
469 | ||
470 | #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ | |
471 | ||
472 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
473 | { | |
474 | } | |
475 | ||
476 | #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ | |
477 | ||
a858af28 PM |
478 | #ifdef CONFIG_RCU_CPU_STALL_INFO |
479 | ||
480 | static void rcu_print_task_stall_begin(struct rcu_node *rnp) | |
481 | { | |
482 | printk(KERN_ERR "\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", | |
483 | rnp->level, rnp->grplo, rnp->grphi); | |
484 | } | |
485 | ||
486 | static void rcu_print_task_stall_end(void) | |
487 | { | |
488 | printk(KERN_CONT "\n"); | |
489 | } | |
490 | ||
491 | #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ | |
492 | ||
493 | static void rcu_print_task_stall_begin(struct rcu_node *rnp) | |
494 | { | |
495 | } | |
496 | ||
497 | static void rcu_print_task_stall_end(void) | |
498 | { | |
499 | } | |
500 | ||
501 | #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */ | |
502 | ||
f41d911f PM |
503 | /* |
504 | * Scan the current list of tasks blocked within RCU read-side critical | |
505 | * sections, printing out the tid of each. | |
506 | */ | |
9bc8b558 | 507 | static int rcu_print_task_stall(struct rcu_node *rnp) |
f41d911f | 508 | { |
f41d911f | 509 | struct task_struct *t; |
9bc8b558 | 510 | int ndetected = 0; |
f41d911f | 511 | |
27f4d280 | 512 | if (!rcu_preempt_blocked_readers_cgp(rnp)) |
9bc8b558 | 513 | return 0; |
a858af28 | 514 | rcu_print_task_stall_begin(rnp); |
12f5f524 PM |
515 | t = list_entry(rnp->gp_tasks, |
516 | struct task_struct, rcu_node_entry); | |
9bc8b558 | 517 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { |
a858af28 | 518 | printk(KERN_CONT " P%d", t->pid); |
9bc8b558 PM |
519 | ndetected++; |
520 | } | |
a858af28 | 521 | rcu_print_task_stall_end(); |
9bc8b558 | 522 | return ndetected; |
f41d911f PM |
523 | } |
524 | ||
b0e165c0 PM |
525 | /* |
526 | * Check that the list of blocked tasks for the newly completed grace | |
527 | * period is in fact empty. It is a serious bug to complete a grace | |
528 | * period that still has RCU readers blocked! This function must be | |
529 | * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock | |
530 | * must be held by the caller. | |
12f5f524 PM |
531 | * |
532 | * Also, if there are blocked tasks on the list, they automatically | |
533 | * block the newly created grace period, so set up ->gp_tasks accordingly. | |
b0e165c0 PM |
534 | */ |
535 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
536 | { | |
27f4d280 | 537 | WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)); |
12f5f524 PM |
538 | if (!list_empty(&rnp->blkd_tasks)) |
539 | rnp->gp_tasks = rnp->blkd_tasks.next; | |
28ecd580 | 540 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
541 | } |
542 | ||
33f76148 PM |
543 | #ifdef CONFIG_HOTPLUG_CPU |
544 | ||
dd5d19ba PM |
545 | /* |
546 | * Handle tasklist migration for case in which all CPUs covered by the | |
547 | * specified rcu_node have gone offline. Move them up to the root | |
548 | * rcu_node. The reason for not just moving them to the immediate | |
549 | * parent is to remove the need for rcu_read_unlock_special() to | |
550 | * make more than two attempts to acquire the target rcu_node's lock. | |
b668c9cf PM |
551 | * Returns true if there were tasks blocking the current RCU grace |
552 | * period. | |
dd5d19ba | 553 | * |
237c80c5 PM |
554 | * Returns 1 if there was previously a task blocking the current grace |
555 | * period on the specified rcu_node structure. | |
556 | * | |
dd5d19ba PM |
557 | * The caller must hold rnp->lock with irqs disabled. |
558 | */ | |
237c80c5 PM |
559 | static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
560 | struct rcu_node *rnp, | |
561 | struct rcu_data *rdp) | |
dd5d19ba | 562 | { |
dd5d19ba PM |
563 | struct list_head *lp; |
564 | struct list_head *lp_root; | |
d9a3da06 | 565 | int retval = 0; |
dd5d19ba | 566 | struct rcu_node *rnp_root = rcu_get_root(rsp); |
12f5f524 | 567 | struct task_struct *t; |
dd5d19ba | 568 | |
86848966 PM |
569 | if (rnp == rnp_root) { |
570 | WARN_ONCE(1, "Last CPU thought to be offlined?"); | |
237c80c5 | 571 | return 0; /* Shouldn't happen: at least one CPU online. */ |
86848966 | 572 | } |
12f5f524 PM |
573 | |
574 | /* If we are on an internal node, complain bitterly. */ | |
575 | WARN_ON_ONCE(rnp != rdp->mynode); | |
dd5d19ba PM |
576 | |
577 | /* | |
12f5f524 PM |
578 | * Move tasks up to root rcu_node. Don't try to get fancy for |
579 | * this corner-case operation -- just put this node's tasks | |
580 | * at the head of the root node's list, and update the root node's | |
581 | * ->gp_tasks and ->exp_tasks pointers to those of this node's, | |
582 | * if non-NULL. This might result in waiting for more tasks than | |
583 | * absolutely necessary, but this is a good performance/complexity | |
584 | * tradeoff. | |
dd5d19ba | 585 | */ |
2036d94a | 586 | if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0) |
d9a3da06 PM |
587 | retval |= RCU_OFL_TASKS_NORM_GP; |
588 | if (rcu_preempted_readers_exp(rnp)) | |
589 | retval |= RCU_OFL_TASKS_EXP_GP; | |
12f5f524 PM |
590 | lp = &rnp->blkd_tasks; |
591 | lp_root = &rnp_root->blkd_tasks; | |
592 | while (!list_empty(lp)) { | |
593 | t = list_entry(lp->next, typeof(*t), rcu_node_entry); | |
594 | raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ | |
595 | list_del(&t->rcu_node_entry); | |
596 | t->rcu_blocked_node = rnp_root; | |
597 | list_add(&t->rcu_node_entry, lp_root); | |
598 | if (&t->rcu_node_entry == rnp->gp_tasks) | |
599 | rnp_root->gp_tasks = rnp->gp_tasks; | |
600 | if (&t->rcu_node_entry == rnp->exp_tasks) | |
601 | rnp_root->exp_tasks = rnp->exp_tasks; | |
27f4d280 PM |
602 | #ifdef CONFIG_RCU_BOOST |
603 | if (&t->rcu_node_entry == rnp->boost_tasks) | |
604 | rnp_root->boost_tasks = rnp->boost_tasks; | |
605 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
12f5f524 | 606 | raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ |
dd5d19ba | 607 | } |
27f4d280 | 608 | |
1e3fd2b3 PM |
609 | rnp->gp_tasks = NULL; |
610 | rnp->exp_tasks = NULL; | |
27f4d280 | 611 | #ifdef CONFIG_RCU_BOOST |
1e3fd2b3 | 612 | rnp->boost_tasks = NULL; |
5cc900cf PM |
613 | /* |
614 | * In case root is being boosted and leaf was not. Make sure | |
615 | * that we boost the tasks blocking the current grace period | |
616 | * in this case. | |
617 | */ | |
27f4d280 PM |
618 | raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ |
619 | if (rnp_root->boost_tasks != NULL && | |
5cc900cf PM |
620 | rnp_root->boost_tasks != rnp_root->gp_tasks && |
621 | rnp_root->boost_tasks != rnp_root->exp_tasks) | |
27f4d280 PM |
622 | rnp_root->boost_tasks = rnp_root->gp_tasks; |
623 | raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ | |
624 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
625 | ||
237c80c5 | 626 | return retval; |
dd5d19ba PM |
627 | } |
628 | ||
e5601400 PM |
629 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
630 | ||
f41d911f PM |
631 | /* |
632 | * Check for a quiescent state from the current CPU. When a task blocks, | |
633 | * the task is recorded in the corresponding CPU's rcu_node structure, | |
634 | * which is checked elsewhere. | |
635 | * | |
636 | * Caller must disable hard irqs. | |
637 | */ | |
638 | static void rcu_preempt_check_callbacks(int cpu) | |
639 | { | |
640 | struct task_struct *t = current; | |
641 | ||
642 | if (t->rcu_read_lock_nesting == 0) { | |
c3422bea | 643 | rcu_preempt_qs(cpu); |
f41d911f PM |
644 | return; |
645 | } | |
10f39bb1 PM |
646 | if (t->rcu_read_lock_nesting > 0 && |
647 | per_cpu(rcu_preempt_data, cpu).qs_pending) | |
c3422bea | 648 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; |
f41d911f PM |
649 | } |
650 | ||
a46e0899 PM |
651 | #ifdef CONFIG_RCU_BOOST |
652 | ||
09223371 SL |
653 | static void rcu_preempt_do_callbacks(void) |
654 | { | |
655 | rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data)); | |
656 | } | |
657 | ||
a46e0899 PM |
658 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
659 | ||
f41d911f | 660 | /* |
6cc68793 | 661 | * Queue a preemptible-RCU callback for invocation after a grace period. |
f41d911f PM |
662 | */ |
663 | void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) | |
664 | { | |
3fbfbf7a | 665 | __call_rcu(head, func, &rcu_preempt_state, -1, 0); |
f41d911f PM |
666 | } |
667 | EXPORT_SYMBOL_GPL(call_rcu); | |
668 | ||
486e2593 PM |
669 | /* |
670 | * Queue an RCU callback for lazy invocation after a grace period. | |
671 | * This will likely be later named something like "call_rcu_lazy()", | |
672 | * but this change will require some way of tagging the lazy RCU | |
673 | * callbacks in the list of pending callbacks. Until then, this | |
674 | * function may only be called from __kfree_rcu(). | |
675 | */ | |
676 | void kfree_call_rcu(struct rcu_head *head, | |
677 | void (*func)(struct rcu_head *rcu)) | |
678 | { | |
3fbfbf7a | 679 | __call_rcu(head, func, &rcu_preempt_state, -1, 1); |
486e2593 PM |
680 | } |
681 | EXPORT_SYMBOL_GPL(kfree_call_rcu); | |
682 | ||
6ebb237b PM |
683 | /** |
684 | * synchronize_rcu - wait until a grace period has elapsed. | |
685 | * | |
686 | * Control will return to the caller some time after a full grace | |
687 | * period has elapsed, in other words after all currently executing RCU | |
77d8485a PM |
688 | * read-side critical sections have completed. Note, however, that |
689 | * upon return from synchronize_rcu(), the caller might well be executing | |
690 | * concurrently with new RCU read-side critical sections that began while | |
691 | * synchronize_rcu() was waiting. RCU read-side critical sections are | |
692 | * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. | |
f0a0e6f2 PM |
693 | * |
694 | * See the description of synchronize_sched() for more detailed information | |
695 | * on memory ordering guarantees. | |
6ebb237b PM |
696 | */ |
697 | void synchronize_rcu(void) | |
698 | { | |
fe15d706 PM |
699 | rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && |
700 | !lock_is_held(&rcu_lock_map) && | |
701 | !lock_is_held(&rcu_sched_lock_map), | |
702 | "Illegal synchronize_rcu() in RCU read-side critical section"); | |
6ebb237b PM |
703 | if (!rcu_scheduler_active) |
704 | return; | |
3705b88d AM |
705 | if (rcu_expedited) |
706 | synchronize_rcu_expedited(); | |
707 | else | |
708 | wait_rcu_gp(call_rcu); | |
6ebb237b PM |
709 | } |
710 | EXPORT_SYMBOL_GPL(synchronize_rcu); | |
711 | ||
d9a3da06 | 712 | static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); |
bcfa57ce | 713 | static unsigned long sync_rcu_preempt_exp_count; |
d9a3da06 PM |
714 | static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); |
715 | ||
716 | /* | |
717 | * Return non-zero if there are any tasks in RCU read-side critical | |
718 | * sections blocking the current preemptible-RCU expedited grace period. | |
719 | * If there is no preemptible-RCU expedited grace period currently in | |
720 | * progress, returns zero unconditionally. | |
721 | */ | |
722 | static int rcu_preempted_readers_exp(struct rcu_node *rnp) | |
723 | { | |
12f5f524 | 724 | return rnp->exp_tasks != NULL; |
d9a3da06 PM |
725 | } |
726 | ||
727 | /* | |
728 | * return non-zero if there is no RCU expedited grace period in progress | |
729 | * for the specified rcu_node structure, in other words, if all CPUs and | |
730 | * tasks covered by the specified rcu_node structure have done their bit | |
731 | * for the current expedited grace period. Works only for preemptible | |
732 | * RCU -- other RCU implementation use other means. | |
733 | * | |
734 | * Caller must hold sync_rcu_preempt_exp_mutex. | |
735 | */ | |
736 | static int sync_rcu_preempt_exp_done(struct rcu_node *rnp) | |
737 | { | |
738 | return !rcu_preempted_readers_exp(rnp) && | |
739 | ACCESS_ONCE(rnp->expmask) == 0; | |
740 | } | |
741 | ||
742 | /* | |
743 | * Report the exit from RCU read-side critical section for the last task | |
744 | * that queued itself during or before the current expedited preemptible-RCU | |
745 | * grace period. This event is reported either to the rcu_node structure on | |
746 | * which the task was queued or to one of that rcu_node structure's ancestors, | |
747 | * recursively up the tree. (Calm down, calm down, we do the recursion | |
748 | * iteratively!) | |
749 | * | |
b40d293e TG |
750 | * Most callers will set the "wake" flag, but the task initiating the |
751 | * expedited grace period need not wake itself. | |
752 | * | |
d9a3da06 PM |
753 | * Caller must hold sync_rcu_preempt_exp_mutex. |
754 | */ | |
b40d293e TG |
755 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, |
756 | bool wake) | |
d9a3da06 PM |
757 | { |
758 | unsigned long flags; | |
759 | unsigned long mask; | |
760 | ||
1304afb2 | 761 | raw_spin_lock_irqsave(&rnp->lock, flags); |
d9a3da06 | 762 | for (;;) { |
131906b0 PM |
763 | if (!sync_rcu_preempt_exp_done(rnp)) { |
764 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
d9a3da06 | 765 | break; |
131906b0 | 766 | } |
d9a3da06 | 767 | if (rnp->parent == NULL) { |
131906b0 | 768 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b40d293e TG |
769 | if (wake) |
770 | wake_up(&sync_rcu_preempt_exp_wq); | |
d9a3da06 PM |
771 | break; |
772 | } | |
773 | mask = rnp->grpmask; | |
1304afb2 | 774 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ |
d9a3da06 | 775 | rnp = rnp->parent; |
1304afb2 | 776 | raw_spin_lock(&rnp->lock); /* irqs already disabled */ |
d9a3da06 PM |
777 | rnp->expmask &= ~mask; |
778 | } | |
d9a3da06 PM |
779 | } |
780 | ||
781 | /* | |
782 | * Snapshot the tasks blocking the newly started preemptible-RCU expedited | |
783 | * grace period for the specified rcu_node structure. If there are no such | |
784 | * tasks, report it up the rcu_node hierarchy. | |
785 | * | |
7b2e6011 PM |
786 | * Caller must hold sync_rcu_preempt_exp_mutex and must exclude |
787 | * CPU hotplug operations. | |
d9a3da06 PM |
788 | */ |
789 | static void | |
790 | sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) | |
791 | { | |
1217ed1b | 792 | unsigned long flags; |
12f5f524 | 793 | int must_wait = 0; |
d9a3da06 | 794 | |
1217ed1b | 795 | raw_spin_lock_irqsave(&rnp->lock, flags); |
c701d5d9 | 796 | if (list_empty(&rnp->blkd_tasks)) { |
1217ed1b | 797 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
c701d5d9 | 798 | } else { |
12f5f524 | 799 | rnp->exp_tasks = rnp->blkd_tasks.next; |
1217ed1b | 800 | rcu_initiate_boost(rnp, flags); /* releases rnp->lock */ |
12f5f524 PM |
801 | must_wait = 1; |
802 | } | |
d9a3da06 | 803 | if (!must_wait) |
b40d293e | 804 | rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */ |
d9a3da06 PM |
805 | } |
806 | ||
236fefaf PM |
807 | /** |
808 | * synchronize_rcu_expedited - Brute-force RCU grace period | |
809 | * | |
810 | * Wait for an RCU-preempt grace period, but expedite it. The basic | |
811 | * idea is to invoke synchronize_sched_expedited() to push all the tasks to | |
812 | * the ->blkd_tasks lists and wait for this list to drain. This consumes | |
813 | * significant time on all CPUs and is unfriendly to real-time workloads, | |
814 | * so is thus not recommended for any sort of common-case code. | |
815 | * In fact, if you are using synchronize_rcu_expedited() in a loop, | |
816 | * please restructure your code to batch your updates, and then Use a | |
817 | * single synchronize_rcu() instead. | |
818 | * | |
819 | * Note that it is illegal to call this function while holding any lock | |
820 | * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal | |
821 | * to call this function from a CPU-hotplug notifier. Failing to observe | |
822 | * these restriction will result in deadlock. | |
019129d5 PM |
823 | */ |
824 | void synchronize_rcu_expedited(void) | |
825 | { | |
d9a3da06 PM |
826 | unsigned long flags; |
827 | struct rcu_node *rnp; | |
828 | struct rcu_state *rsp = &rcu_preempt_state; | |
bcfa57ce | 829 | unsigned long snap; |
d9a3da06 PM |
830 | int trycount = 0; |
831 | ||
832 | smp_mb(); /* Caller's modifications seen first by other CPUs. */ | |
833 | snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1; | |
834 | smp_mb(); /* Above access cannot bleed into critical section. */ | |
835 | ||
1943c89d PM |
836 | /* |
837 | * Block CPU-hotplug operations. This means that any CPU-hotplug | |
838 | * operation that finds an rcu_node structure with tasks in the | |
839 | * process of being boosted will know that all tasks blocking | |
840 | * this expedited grace period will already be in the process of | |
841 | * being boosted. This simplifies the process of moving tasks | |
842 | * from leaf to root rcu_node structures. | |
843 | */ | |
844 | get_online_cpus(); | |
845 | ||
d9a3da06 PM |
846 | /* |
847 | * Acquire lock, falling back to synchronize_rcu() if too many | |
848 | * lock-acquisition failures. Of course, if someone does the | |
849 | * expedited grace period for us, just leave. | |
850 | */ | |
851 | while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) { | |
1943c89d PM |
852 | if (ULONG_CMP_LT(snap, |
853 | ACCESS_ONCE(sync_rcu_preempt_exp_count))) { | |
854 | put_online_cpus(); | |
855 | goto mb_ret; /* Others did our work for us. */ | |
856 | } | |
c701d5d9 | 857 | if (trycount++ < 10) { |
d9a3da06 | 858 | udelay(trycount * num_online_cpus()); |
c701d5d9 | 859 | } else { |
1943c89d | 860 | put_online_cpus(); |
3705b88d | 861 | wait_rcu_gp(call_rcu); |
d9a3da06 PM |
862 | return; |
863 | } | |
d9a3da06 | 864 | } |
1943c89d PM |
865 | if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) { |
866 | put_online_cpus(); | |
d9a3da06 | 867 | goto unlock_mb_ret; /* Others did our work for us. */ |
1943c89d | 868 | } |
d9a3da06 | 869 | |
12f5f524 | 870 | /* force all RCU readers onto ->blkd_tasks lists. */ |
d9a3da06 PM |
871 | synchronize_sched_expedited(); |
872 | ||
d9a3da06 PM |
873 | /* Initialize ->expmask for all non-leaf rcu_node structures. */ |
874 | rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) { | |
1943c89d | 875 | raw_spin_lock_irqsave(&rnp->lock, flags); |
d9a3da06 | 876 | rnp->expmask = rnp->qsmaskinit; |
1943c89d | 877 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
d9a3da06 PM |
878 | } |
879 | ||
12f5f524 | 880 | /* Snapshot current state of ->blkd_tasks lists. */ |
d9a3da06 PM |
881 | rcu_for_each_leaf_node(rsp, rnp) |
882 | sync_rcu_preempt_exp_init(rsp, rnp); | |
883 | if (NUM_RCU_NODES > 1) | |
884 | sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp)); | |
885 | ||
1943c89d | 886 | put_online_cpus(); |
d9a3da06 | 887 | |
12f5f524 | 888 | /* Wait for snapshotted ->blkd_tasks lists to drain. */ |
d9a3da06 PM |
889 | rnp = rcu_get_root(rsp); |
890 | wait_event(sync_rcu_preempt_exp_wq, | |
891 | sync_rcu_preempt_exp_done(rnp)); | |
892 | ||
893 | /* Clean up and exit. */ | |
894 | smp_mb(); /* ensure expedited GP seen before counter increment. */ | |
895 | ACCESS_ONCE(sync_rcu_preempt_exp_count)++; | |
896 | unlock_mb_ret: | |
897 | mutex_unlock(&sync_rcu_preempt_exp_mutex); | |
898 | mb_ret: | |
899 | smp_mb(); /* ensure subsequent action seen after grace period. */ | |
019129d5 PM |
900 | } |
901 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
902 | ||
e74f4c45 PM |
903 | /** |
904 | * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. | |
f0a0e6f2 PM |
905 | * |
906 | * Note that this primitive does not necessarily wait for an RCU grace period | |
907 | * to complete. For example, if there are no RCU callbacks queued anywhere | |
908 | * in the system, then rcu_barrier() is within its rights to return | |
909 | * immediately, without waiting for anything, much less an RCU grace period. | |
e74f4c45 PM |
910 | */ |
911 | void rcu_barrier(void) | |
912 | { | |
037b64ed | 913 | _rcu_barrier(&rcu_preempt_state); |
e74f4c45 PM |
914 | } |
915 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
916 | ||
1eba8f84 | 917 | /* |
6cc68793 | 918 | * Initialize preemptible RCU's state structures. |
1eba8f84 PM |
919 | */ |
920 | static void __init __rcu_init_preempt(void) | |
921 | { | |
394f99a9 | 922 | rcu_init_one(&rcu_preempt_state, &rcu_preempt_data); |
1eba8f84 PM |
923 | } |
924 | ||
f41d911f PM |
925 | #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ |
926 | ||
27f4d280 PM |
927 | static struct rcu_state *rcu_state = &rcu_sched_state; |
928 | ||
f41d911f PM |
929 | /* |
930 | * Tell them what RCU they are running. | |
931 | */ | |
0e0fc1c2 | 932 | static void __init rcu_bootup_announce(void) |
f41d911f PM |
933 | { |
934 | printk(KERN_INFO "Hierarchical RCU implementation.\n"); | |
26845c28 | 935 | rcu_bootup_announce_oddness(); |
f41d911f PM |
936 | } |
937 | ||
938 | /* | |
939 | * Return the number of RCU batches processed thus far for debug & stats. | |
940 | */ | |
941 | long rcu_batches_completed(void) | |
942 | { | |
943 | return rcu_batches_completed_sched(); | |
944 | } | |
945 | EXPORT_SYMBOL_GPL(rcu_batches_completed); | |
946 | ||
bf66f18e PM |
947 | /* |
948 | * Force a quiescent state for RCU, which, because there is no preemptible | |
949 | * RCU, becomes the same as rcu-sched. | |
950 | */ | |
951 | void rcu_force_quiescent_state(void) | |
952 | { | |
953 | rcu_sched_force_quiescent_state(); | |
954 | } | |
955 | EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); | |
956 | ||
cba6d0d6 PM |
957 | /* |
958 | * Because preemptible RCU does not exist, we never have to check for | |
959 | * CPUs being in quiescent states. | |
960 | */ | |
961 | static void rcu_preempt_note_context_switch(int cpu) | |
962 | { | |
963 | } | |
964 | ||
fc2219d4 | 965 | /* |
6cc68793 | 966 | * Because preemptible RCU does not exist, there are never any preempted |
fc2219d4 PM |
967 | * RCU readers. |
968 | */ | |
27f4d280 | 969 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
fc2219d4 PM |
970 | { |
971 | return 0; | |
972 | } | |
973 | ||
b668c9cf PM |
974 | #ifdef CONFIG_HOTPLUG_CPU |
975 | ||
976 | /* Because preemptible RCU does not exist, no quieting of tasks. */ | |
d3f6bad3 | 977 | static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
b668c9cf | 978 | { |
1304afb2 | 979 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b668c9cf PM |
980 | } |
981 | ||
982 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
983 | ||
1ed509a2 | 984 | /* |
6cc68793 | 985 | * Because preemptible RCU does not exist, we never have to check for |
1ed509a2 PM |
986 | * tasks blocked within RCU read-side critical sections. |
987 | */ | |
988 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
989 | { | |
990 | } | |
991 | ||
f41d911f | 992 | /* |
6cc68793 | 993 | * Because preemptible RCU does not exist, we never have to check for |
f41d911f PM |
994 | * tasks blocked within RCU read-side critical sections. |
995 | */ | |
9bc8b558 | 996 | static int rcu_print_task_stall(struct rcu_node *rnp) |
f41d911f | 997 | { |
9bc8b558 | 998 | return 0; |
f41d911f PM |
999 | } |
1000 | ||
b0e165c0 | 1001 | /* |
6cc68793 | 1002 | * Because there is no preemptible RCU, there can be no readers blocked, |
49e29126 PM |
1003 | * so there is no need to check for blocked tasks. So check only for |
1004 | * bogus qsmask values. | |
b0e165c0 PM |
1005 | */ |
1006 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
1007 | { | |
49e29126 | 1008 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
1009 | } |
1010 | ||
33f76148 PM |
1011 | #ifdef CONFIG_HOTPLUG_CPU |
1012 | ||
dd5d19ba | 1013 | /* |
6cc68793 | 1014 | * Because preemptible RCU does not exist, it never needs to migrate |
237c80c5 PM |
1015 | * tasks that were blocked within RCU read-side critical sections, and |
1016 | * such non-existent tasks cannot possibly have been blocking the current | |
1017 | * grace period. | |
dd5d19ba | 1018 | */ |
237c80c5 PM |
1019 | static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
1020 | struct rcu_node *rnp, | |
1021 | struct rcu_data *rdp) | |
dd5d19ba | 1022 | { |
237c80c5 | 1023 | return 0; |
dd5d19ba PM |
1024 | } |
1025 | ||
e5601400 PM |
1026 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
1027 | ||
f41d911f | 1028 | /* |
6cc68793 | 1029 | * Because preemptible RCU does not exist, it never has any callbacks |
f41d911f PM |
1030 | * to check. |
1031 | */ | |
1eba8f84 | 1032 | static void rcu_preempt_check_callbacks(int cpu) |
f41d911f PM |
1033 | { |
1034 | } | |
1035 | ||
486e2593 PM |
1036 | /* |
1037 | * Queue an RCU callback for lazy invocation after a grace period. | |
1038 | * This will likely be later named something like "call_rcu_lazy()", | |
1039 | * but this change will require some way of tagging the lazy RCU | |
1040 | * callbacks in the list of pending callbacks. Until then, this | |
1041 | * function may only be called from __kfree_rcu(). | |
1042 | * | |
1043 | * Because there is no preemptible RCU, we use RCU-sched instead. | |
1044 | */ | |
1045 | void kfree_call_rcu(struct rcu_head *head, | |
1046 | void (*func)(struct rcu_head *rcu)) | |
1047 | { | |
3fbfbf7a | 1048 | __call_rcu(head, func, &rcu_sched_state, -1, 1); |
486e2593 PM |
1049 | } |
1050 | EXPORT_SYMBOL_GPL(kfree_call_rcu); | |
1051 | ||
019129d5 PM |
1052 | /* |
1053 | * Wait for an rcu-preempt grace period, but make it happen quickly. | |
6cc68793 | 1054 | * But because preemptible RCU does not exist, map to rcu-sched. |
019129d5 PM |
1055 | */ |
1056 | void synchronize_rcu_expedited(void) | |
1057 | { | |
1058 | synchronize_sched_expedited(); | |
1059 | } | |
1060 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
1061 | ||
d9a3da06 PM |
1062 | #ifdef CONFIG_HOTPLUG_CPU |
1063 | ||
1064 | /* | |
6cc68793 | 1065 | * Because preemptible RCU does not exist, there is never any need to |
d9a3da06 PM |
1066 | * report on tasks preempted in RCU read-side critical sections during |
1067 | * expedited RCU grace periods. | |
1068 | */ | |
b40d293e TG |
1069 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, |
1070 | bool wake) | |
d9a3da06 | 1071 | { |
d9a3da06 PM |
1072 | } |
1073 | ||
1074 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
1075 | ||
e74f4c45 | 1076 | /* |
6cc68793 | 1077 | * Because preemptible RCU does not exist, rcu_barrier() is just |
e74f4c45 PM |
1078 | * another name for rcu_barrier_sched(). |
1079 | */ | |
1080 | void rcu_barrier(void) | |
1081 | { | |
1082 | rcu_barrier_sched(); | |
1083 | } | |
1084 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
1085 | ||
1eba8f84 | 1086 | /* |
6cc68793 | 1087 | * Because preemptible RCU does not exist, it need not be initialized. |
1eba8f84 PM |
1088 | */ |
1089 | static void __init __rcu_init_preempt(void) | |
1090 | { | |
1091 | } | |
1092 | ||
f41d911f | 1093 | #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ |
8bd93a2c | 1094 | |
27f4d280 PM |
1095 | #ifdef CONFIG_RCU_BOOST |
1096 | ||
1097 | #include "rtmutex_common.h" | |
1098 | ||
0ea1f2eb PM |
1099 | #ifdef CONFIG_RCU_TRACE |
1100 | ||
1101 | static void rcu_initiate_boost_trace(struct rcu_node *rnp) | |
1102 | { | |
1103 | if (list_empty(&rnp->blkd_tasks)) | |
1104 | rnp->n_balk_blkd_tasks++; | |
1105 | else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL) | |
1106 | rnp->n_balk_exp_gp_tasks++; | |
1107 | else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL) | |
1108 | rnp->n_balk_boost_tasks++; | |
1109 | else if (rnp->gp_tasks != NULL && rnp->qsmask != 0) | |
1110 | rnp->n_balk_notblocked++; | |
1111 | else if (rnp->gp_tasks != NULL && | |
a9f4793d | 1112 | ULONG_CMP_LT(jiffies, rnp->boost_time)) |
0ea1f2eb PM |
1113 | rnp->n_balk_notyet++; |
1114 | else | |
1115 | rnp->n_balk_nos++; | |
1116 | } | |
1117 | ||
1118 | #else /* #ifdef CONFIG_RCU_TRACE */ | |
1119 | ||
1120 | static void rcu_initiate_boost_trace(struct rcu_node *rnp) | |
1121 | { | |
1122 | } | |
1123 | ||
1124 | #endif /* #else #ifdef CONFIG_RCU_TRACE */ | |
1125 | ||
5d01bbd1 TG |
1126 | static void rcu_wake_cond(struct task_struct *t, int status) |
1127 | { | |
1128 | /* | |
1129 | * If the thread is yielding, only wake it when this | |
1130 | * is invoked from idle | |
1131 | */ | |
1132 | if (status != RCU_KTHREAD_YIELDING || is_idle_task(current)) | |
1133 | wake_up_process(t); | |
1134 | } | |
1135 | ||
27f4d280 PM |
1136 | /* |
1137 | * Carry out RCU priority boosting on the task indicated by ->exp_tasks | |
1138 | * or ->boost_tasks, advancing the pointer to the next task in the | |
1139 | * ->blkd_tasks list. | |
1140 | * | |
1141 | * Note that irqs must be enabled: boosting the task can block. | |
1142 | * Returns 1 if there are more tasks needing to be boosted. | |
1143 | */ | |
1144 | static int rcu_boost(struct rcu_node *rnp) | |
1145 | { | |
1146 | unsigned long flags; | |
1147 | struct rt_mutex mtx; | |
1148 | struct task_struct *t; | |
1149 | struct list_head *tb; | |
1150 | ||
1151 | if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) | |
1152 | return 0; /* Nothing left to boost. */ | |
1153 | ||
1154 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
1155 | ||
1156 | /* | |
1157 | * Recheck under the lock: all tasks in need of boosting | |
1158 | * might exit their RCU read-side critical sections on their own. | |
1159 | */ | |
1160 | if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { | |
1161 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
1162 | return 0; | |
1163 | } | |
1164 | ||
1165 | /* | |
1166 | * Preferentially boost tasks blocking expedited grace periods. | |
1167 | * This cannot starve the normal grace periods because a second | |
1168 | * expedited grace period must boost all blocked tasks, including | |
1169 | * those blocking the pre-existing normal grace period. | |
1170 | */ | |
0ea1f2eb | 1171 | if (rnp->exp_tasks != NULL) { |
27f4d280 | 1172 | tb = rnp->exp_tasks; |
0ea1f2eb PM |
1173 | rnp->n_exp_boosts++; |
1174 | } else { | |
27f4d280 | 1175 | tb = rnp->boost_tasks; |
0ea1f2eb PM |
1176 | rnp->n_normal_boosts++; |
1177 | } | |
1178 | rnp->n_tasks_boosted++; | |
27f4d280 PM |
1179 | |
1180 | /* | |
1181 | * We boost task t by manufacturing an rt_mutex that appears to | |
1182 | * be held by task t. We leave a pointer to that rt_mutex where | |
1183 | * task t can find it, and task t will release the mutex when it | |
1184 | * exits its outermost RCU read-side critical section. Then | |
1185 | * simply acquiring this artificial rt_mutex will boost task | |
1186 | * t's priority. (Thanks to tglx for suggesting this approach!) | |
1187 | * | |
1188 | * Note that task t must acquire rnp->lock to remove itself from | |
1189 | * the ->blkd_tasks list, which it will do from exit() if from | |
1190 | * nowhere else. We therefore are guaranteed that task t will | |
1191 | * stay around at least until we drop rnp->lock. Note that | |
1192 | * rnp->lock also resolves races between our priority boosting | |
1193 | * and task t's exiting its outermost RCU read-side critical | |
1194 | * section. | |
1195 | */ | |
1196 | t = container_of(tb, struct task_struct, rcu_node_entry); | |
1197 | rt_mutex_init_proxy_locked(&mtx, t); | |
1198 | t->rcu_boost_mutex = &mtx; | |
27f4d280 PM |
1199 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1200 | rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */ | |
1201 | rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ | |
1202 | ||
4f89b336 PM |
1203 | return ACCESS_ONCE(rnp->exp_tasks) != NULL || |
1204 | ACCESS_ONCE(rnp->boost_tasks) != NULL; | |
27f4d280 PM |
1205 | } |
1206 | ||
27f4d280 PM |
1207 | /* |
1208 | * Priority-boosting kthread. One per leaf rcu_node and one for the | |
1209 | * root rcu_node. | |
1210 | */ | |
1211 | static int rcu_boost_kthread(void *arg) | |
1212 | { | |
1213 | struct rcu_node *rnp = (struct rcu_node *)arg; | |
1214 | int spincnt = 0; | |
1215 | int more2boost; | |
1216 | ||
385680a9 | 1217 | trace_rcu_utilization("Start boost kthread@init"); |
27f4d280 | 1218 | for (;;) { |
d71df90e | 1219 | rnp->boost_kthread_status = RCU_KTHREAD_WAITING; |
385680a9 | 1220 | trace_rcu_utilization("End boost kthread@rcu_wait"); |
08bca60a | 1221 | rcu_wait(rnp->boost_tasks || rnp->exp_tasks); |
385680a9 | 1222 | trace_rcu_utilization("Start boost kthread@rcu_wait"); |
d71df90e | 1223 | rnp->boost_kthread_status = RCU_KTHREAD_RUNNING; |
27f4d280 PM |
1224 | more2boost = rcu_boost(rnp); |
1225 | if (more2boost) | |
1226 | spincnt++; | |
1227 | else | |
1228 | spincnt = 0; | |
1229 | if (spincnt > 10) { | |
5d01bbd1 | 1230 | rnp->boost_kthread_status = RCU_KTHREAD_YIELDING; |
385680a9 | 1231 | trace_rcu_utilization("End boost kthread@rcu_yield"); |
5d01bbd1 | 1232 | schedule_timeout_interruptible(2); |
385680a9 | 1233 | trace_rcu_utilization("Start boost kthread@rcu_yield"); |
27f4d280 PM |
1234 | spincnt = 0; |
1235 | } | |
1236 | } | |
1217ed1b | 1237 | /* NOTREACHED */ |
385680a9 | 1238 | trace_rcu_utilization("End boost kthread@notreached"); |
27f4d280 PM |
1239 | return 0; |
1240 | } | |
1241 | ||
1242 | /* | |
1243 | * Check to see if it is time to start boosting RCU readers that are | |
1244 | * blocking the current grace period, and, if so, tell the per-rcu_node | |
1245 | * kthread to start boosting them. If there is an expedited grace | |
1246 | * period in progress, it is always time to boost. | |
1247 | * | |
b065a853 PM |
1248 | * The caller must hold rnp->lock, which this function releases. |
1249 | * The ->boost_kthread_task is immortal, so we don't need to worry | |
1250 | * about it going away. | |
27f4d280 | 1251 | */ |
1217ed1b | 1252 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
27f4d280 PM |
1253 | { |
1254 | struct task_struct *t; | |
1255 | ||
0ea1f2eb PM |
1256 | if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { |
1257 | rnp->n_balk_exp_gp_tasks++; | |
1217ed1b | 1258 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 | 1259 | return; |
0ea1f2eb | 1260 | } |
27f4d280 PM |
1261 | if (rnp->exp_tasks != NULL || |
1262 | (rnp->gp_tasks != NULL && | |
1263 | rnp->boost_tasks == NULL && | |
1264 | rnp->qsmask == 0 && | |
1265 | ULONG_CMP_GE(jiffies, rnp->boost_time))) { | |
1266 | if (rnp->exp_tasks == NULL) | |
1267 | rnp->boost_tasks = rnp->gp_tasks; | |
1217ed1b | 1268 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 | 1269 | t = rnp->boost_kthread_task; |
5d01bbd1 TG |
1270 | if (t) |
1271 | rcu_wake_cond(t, rnp->boost_kthread_status); | |
1217ed1b | 1272 | } else { |
0ea1f2eb | 1273 | rcu_initiate_boost_trace(rnp); |
1217ed1b PM |
1274 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1275 | } | |
27f4d280 PM |
1276 | } |
1277 | ||
a46e0899 PM |
1278 | /* |
1279 | * Wake up the per-CPU kthread to invoke RCU callbacks. | |
1280 | */ | |
1281 | static void invoke_rcu_callbacks_kthread(void) | |
1282 | { | |
1283 | unsigned long flags; | |
1284 | ||
1285 | local_irq_save(flags); | |
1286 | __this_cpu_write(rcu_cpu_has_work, 1); | |
1eb52121 | 1287 | if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && |
5d01bbd1 TG |
1288 | current != __this_cpu_read(rcu_cpu_kthread_task)) { |
1289 | rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task), | |
1290 | __this_cpu_read(rcu_cpu_kthread_status)); | |
1291 | } | |
a46e0899 PM |
1292 | local_irq_restore(flags); |
1293 | } | |
1294 | ||
dff1672d PM |
1295 | /* |
1296 | * Is the current CPU running the RCU-callbacks kthread? | |
1297 | * Caller must have preemption disabled. | |
1298 | */ | |
1299 | static bool rcu_is_callbacks_kthread(void) | |
1300 | { | |
1301 | return __get_cpu_var(rcu_cpu_kthread_task) == current; | |
1302 | } | |
1303 | ||
27f4d280 PM |
1304 | #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) |
1305 | ||
1306 | /* | |
1307 | * Do priority-boost accounting for the start of a new grace period. | |
1308 | */ | |
1309 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) | |
1310 | { | |
1311 | rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; | |
1312 | } | |
1313 | ||
27f4d280 PM |
1314 | /* |
1315 | * Create an RCU-boost kthread for the specified node if one does not | |
1316 | * already exist. We only create this kthread for preemptible RCU. | |
1317 | * Returns zero if all is well, a negated errno otherwise. | |
1318 | */ | |
1319 | static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, | |
5d01bbd1 | 1320 | struct rcu_node *rnp) |
27f4d280 | 1321 | { |
5d01bbd1 | 1322 | int rnp_index = rnp - &rsp->node[0]; |
27f4d280 PM |
1323 | unsigned long flags; |
1324 | struct sched_param sp; | |
1325 | struct task_struct *t; | |
1326 | ||
1327 | if (&rcu_preempt_state != rsp) | |
1328 | return 0; | |
5d01bbd1 TG |
1329 | |
1330 | if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0) | |
1331 | return 0; | |
1332 | ||
a46e0899 | 1333 | rsp->boost = 1; |
27f4d280 PM |
1334 | if (rnp->boost_kthread_task != NULL) |
1335 | return 0; | |
1336 | t = kthread_create(rcu_boost_kthread, (void *)rnp, | |
5b61b0ba | 1337 | "rcub/%d", rnp_index); |
27f4d280 PM |
1338 | if (IS_ERR(t)) |
1339 | return PTR_ERR(t); | |
1340 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
1341 | rnp->boost_kthread_task = t; | |
1342 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
5b61b0ba | 1343 | sp.sched_priority = RCU_BOOST_PRIO; |
27f4d280 | 1344 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); |
9a432736 | 1345 | wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ |
27f4d280 PM |
1346 | return 0; |
1347 | } | |
1348 | ||
f8b7fc6b PM |
1349 | static void rcu_kthread_do_work(void) |
1350 | { | |
1351 | rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data)); | |
1352 | rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data)); | |
1353 | rcu_preempt_do_callbacks(); | |
1354 | } | |
1355 | ||
62ab7072 | 1356 | static void rcu_cpu_kthread_setup(unsigned int cpu) |
f8b7fc6b | 1357 | { |
f8b7fc6b | 1358 | struct sched_param sp; |
f8b7fc6b | 1359 | |
62ab7072 PM |
1360 | sp.sched_priority = RCU_KTHREAD_PRIO; |
1361 | sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); | |
f8b7fc6b PM |
1362 | } |
1363 | ||
62ab7072 | 1364 | static void rcu_cpu_kthread_park(unsigned int cpu) |
f8b7fc6b | 1365 | { |
62ab7072 | 1366 | per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; |
f8b7fc6b PM |
1367 | } |
1368 | ||
62ab7072 | 1369 | static int rcu_cpu_kthread_should_run(unsigned int cpu) |
f8b7fc6b | 1370 | { |
62ab7072 | 1371 | return __get_cpu_var(rcu_cpu_has_work); |
f8b7fc6b PM |
1372 | } |
1373 | ||
1374 | /* | |
1375 | * Per-CPU kernel thread that invokes RCU callbacks. This replaces the | |
e0f23060 PM |
1376 | * RCU softirq used in flavors and configurations of RCU that do not |
1377 | * support RCU priority boosting. | |
f8b7fc6b | 1378 | */ |
62ab7072 | 1379 | static void rcu_cpu_kthread(unsigned int cpu) |
f8b7fc6b | 1380 | { |
62ab7072 PM |
1381 | unsigned int *statusp = &__get_cpu_var(rcu_cpu_kthread_status); |
1382 | char work, *workp = &__get_cpu_var(rcu_cpu_has_work); | |
1383 | int spincnt; | |
f8b7fc6b | 1384 | |
62ab7072 | 1385 | for (spincnt = 0; spincnt < 10; spincnt++) { |
385680a9 | 1386 | trace_rcu_utilization("Start CPU kthread@rcu_wait"); |
f8b7fc6b | 1387 | local_bh_disable(); |
f8b7fc6b | 1388 | *statusp = RCU_KTHREAD_RUNNING; |
62ab7072 PM |
1389 | this_cpu_inc(rcu_cpu_kthread_loops); |
1390 | local_irq_disable(); | |
f8b7fc6b PM |
1391 | work = *workp; |
1392 | *workp = 0; | |
62ab7072 | 1393 | local_irq_enable(); |
f8b7fc6b PM |
1394 | if (work) |
1395 | rcu_kthread_do_work(); | |
1396 | local_bh_enable(); | |
62ab7072 PM |
1397 | if (*workp == 0) { |
1398 | trace_rcu_utilization("End CPU kthread@rcu_wait"); | |
1399 | *statusp = RCU_KTHREAD_WAITING; | |
1400 | return; | |
f8b7fc6b PM |
1401 | } |
1402 | } | |
62ab7072 PM |
1403 | *statusp = RCU_KTHREAD_YIELDING; |
1404 | trace_rcu_utilization("Start CPU kthread@rcu_yield"); | |
1405 | schedule_timeout_interruptible(2); | |
1406 | trace_rcu_utilization("End CPU kthread@rcu_yield"); | |
1407 | *statusp = RCU_KTHREAD_WAITING; | |
f8b7fc6b PM |
1408 | } |
1409 | ||
1410 | /* | |
1411 | * Set the per-rcu_node kthread's affinity to cover all CPUs that are | |
1412 | * served by the rcu_node in question. The CPU hotplug lock is still | |
1413 | * held, so the value of rnp->qsmaskinit will be stable. | |
1414 | * | |
1415 | * We don't include outgoingcpu in the affinity set, use -1 if there is | |
1416 | * no outgoing CPU. If there are no CPUs left in the affinity set, | |
1417 | * this function allows the kthread to execute on any CPU. | |
1418 | */ | |
5d01bbd1 | 1419 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
f8b7fc6b | 1420 | { |
5d01bbd1 TG |
1421 | struct task_struct *t = rnp->boost_kthread_task; |
1422 | unsigned long mask = rnp->qsmaskinit; | |
f8b7fc6b PM |
1423 | cpumask_var_t cm; |
1424 | int cpu; | |
f8b7fc6b | 1425 | |
5d01bbd1 | 1426 | if (!t) |
f8b7fc6b | 1427 | return; |
5d01bbd1 | 1428 | if (!zalloc_cpumask_var(&cm, GFP_KERNEL)) |
f8b7fc6b | 1429 | return; |
f8b7fc6b PM |
1430 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) |
1431 | if ((mask & 0x1) && cpu != outgoingcpu) | |
1432 | cpumask_set_cpu(cpu, cm); | |
1433 | if (cpumask_weight(cm) == 0) { | |
1434 | cpumask_setall(cm); | |
1435 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) | |
1436 | cpumask_clear_cpu(cpu, cm); | |
1437 | WARN_ON_ONCE(cpumask_weight(cm) == 0); | |
1438 | } | |
5d01bbd1 | 1439 | set_cpus_allowed_ptr(t, cm); |
f8b7fc6b PM |
1440 | free_cpumask_var(cm); |
1441 | } | |
1442 | ||
62ab7072 PM |
1443 | static struct smp_hotplug_thread rcu_cpu_thread_spec = { |
1444 | .store = &rcu_cpu_kthread_task, | |
1445 | .thread_should_run = rcu_cpu_kthread_should_run, | |
1446 | .thread_fn = rcu_cpu_kthread, | |
1447 | .thread_comm = "rcuc/%u", | |
1448 | .setup = rcu_cpu_kthread_setup, | |
1449 | .park = rcu_cpu_kthread_park, | |
1450 | }; | |
f8b7fc6b PM |
1451 | |
1452 | /* | |
1453 | * Spawn all kthreads -- called as soon as the scheduler is running. | |
1454 | */ | |
1455 | static int __init rcu_spawn_kthreads(void) | |
1456 | { | |
f8b7fc6b | 1457 | struct rcu_node *rnp; |
5d01bbd1 | 1458 | int cpu; |
f8b7fc6b | 1459 | |
b0d30417 | 1460 | rcu_scheduler_fully_active = 1; |
62ab7072 | 1461 | for_each_possible_cpu(cpu) |
f8b7fc6b | 1462 | per_cpu(rcu_cpu_has_work, cpu) = 0; |
62ab7072 | 1463 | BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec)); |
f8b7fc6b | 1464 | rnp = rcu_get_root(rcu_state); |
5d01bbd1 | 1465 | (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); |
f8b7fc6b PM |
1466 | if (NUM_RCU_NODES > 1) { |
1467 | rcu_for_each_leaf_node(rcu_state, rnp) | |
5d01bbd1 | 1468 | (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); |
f8b7fc6b PM |
1469 | } |
1470 | return 0; | |
1471 | } | |
1472 | early_initcall(rcu_spawn_kthreads); | |
1473 | ||
1474 | static void __cpuinit rcu_prepare_kthreads(int cpu) | |
1475 | { | |
1476 | struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu); | |
1477 | struct rcu_node *rnp = rdp->mynode; | |
1478 | ||
1479 | /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ | |
62ab7072 | 1480 | if (rcu_scheduler_fully_active) |
5d01bbd1 | 1481 | (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); |
f8b7fc6b PM |
1482 | } |
1483 | ||
27f4d280 PM |
1484 | #else /* #ifdef CONFIG_RCU_BOOST */ |
1485 | ||
1217ed1b | 1486 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
27f4d280 | 1487 | { |
1217ed1b | 1488 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 PM |
1489 | } |
1490 | ||
a46e0899 | 1491 | static void invoke_rcu_callbacks_kthread(void) |
27f4d280 | 1492 | { |
a46e0899 | 1493 | WARN_ON_ONCE(1); |
27f4d280 PM |
1494 | } |
1495 | ||
dff1672d PM |
1496 | static bool rcu_is_callbacks_kthread(void) |
1497 | { | |
1498 | return false; | |
1499 | } | |
1500 | ||
27f4d280 PM |
1501 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) |
1502 | { | |
1503 | } | |
1504 | ||
5d01bbd1 | 1505 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
f8b7fc6b PM |
1506 | { |
1507 | } | |
1508 | ||
b0d30417 PM |
1509 | static int __init rcu_scheduler_really_started(void) |
1510 | { | |
1511 | rcu_scheduler_fully_active = 1; | |
1512 | return 0; | |
1513 | } | |
1514 | early_initcall(rcu_scheduler_really_started); | |
1515 | ||
f8b7fc6b PM |
1516 | static void __cpuinit rcu_prepare_kthreads(int cpu) |
1517 | { | |
1518 | } | |
1519 | ||
27f4d280 PM |
1520 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ |
1521 | ||
8bd93a2c PM |
1522 | #if !defined(CONFIG_RCU_FAST_NO_HZ) |
1523 | ||
1524 | /* | |
1525 | * Check to see if any future RCU-related work will need to be done | |
1526 | * by the current CPU, even if none need be done immediately, returning | |
1527 | * 1 if so. This function is part of the RCU implementation; it is -not- | |
1528 | * an exported member of the RCU API. | |
1529 | * | |
7cb92499 PM |
1530 | * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs |
1531 | * any flavor of RCU. | |
8bd93a2c | 1532 | */ |
aa9b1630 | 1533 | int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) |
8bd93a2c | 1534 | { |
aa9b1630 | 1535 | *delta_jiffies = ULONG_MAX; |
aea1b35e PM |
1536 | return rcu_cpu_has_callbacks(cpu); |
1537 | } | |
1538 | ||
7cb92499 PM |
1539 | /* |
1540 | * Because we do not have RCU_FAST_NO_HZ, don't bother initializing for it. | |
1541 | */ | |
1542 | static void rcu_prepare_for_idle_init(int cpu) | |
1543 | { | |
1544 | } | |
1545 | ||
1546 | /* | |
1547 | * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up | |
1548 | * after it. | |
1549 | */ | |
1550 | static void rcu_cleanup_after_idle(int cpu) | |
1551 | { | |
1552 | } | |
1553 | ||
aea1b35e | 1554 | /* |
a858af28 | 1555 | * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n, |
aea1b35e PM |
1556 | * is nothing. |
1557 | */ | |
1558 | static void rcu_prepare_for_idle(int cpu) | |
1559 | { | |
1560 | } | |
1561 | ||
c57afe80 PM |
1562 | /* |
1563 | * Don't bother keeping a running count of the number of RCU callbacks | |
1564 | * posted because CONFIG_RCU_FAST_NO_HZ=n. | |
1565 | */ | |
1566 | static void rcu_idle_count_callbacks_posted(void) | |
1567 | { | |
1568 | } | |
1569 | ||
8bd93a2c PM |
1570 | #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
1571 | ||
f23f7fa1 PM |
1572 | /* |
1573 | * This code is invoked when a CPU goes idle, at which point we want | |
1574 | * to have the CPU do everything required for RCU so that it can enter | |
1575 | * the energy-efficient dyntick-idle mode. This is handled by a | |
1576 | * state machine implemented by rcu_prepare_for_idle() below. | |
1577 | * | |
1578 | * The following three proprocessor symbols control this state machine: | |
1579 | * | |
1580 | * RCU_IDLE_FLUSHES gives the maximum number of times that we will attempt | |
1581 | * to satisfy RCU. Beyond this point, it is better to incur a periodic | |
1582 | * scheduling-clock interrupt than to loop through the state machine | |
1583 | * at full power. | |
1584 | * RCU_IDLE_OPT_FLUSHES gives the number of RCU_IDLE_FLUSHES that are | |
1585 | * optional if RCU does not need anything immediately from this | |
1586 | * CPU, even if this CPU still has RCU callbacks queued. The first | |
1587 | * times through the state machine are mandatory: we need to give | |
1588 | * the state machine a chance to communicate a quiescent state | |
1589 | * to the RCU core. | |
1590 | * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted | |
1591 | * to sleep in dyntick-idle mode with RCU callbacks pending. This | |
1592 | * is sized to be roughly one RCU grace period. Those energy-efficiency | |
1593 | * benchmarkers who might otherwise be tempted to set this to a large | |
1594 | * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your | |
1595 | * system. And if you are -that- concerned about energy efficiency, | |
1596 | * just power the system down and be done with it! | |
778d250a PM |
1597 | * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is |
1598 | * permitted to sleep in dyntick-idle mode with only lazy RCU | |
1599 | * callbacks pending. Setting this too high can OOM your system. | |
f23f7fa1 PM |
1600 | * |
1601 | * The values below work well in practice. If future workloads require | |
1602 | * adjustment, they can be converted into kernel config parameters, though | |
1603 | * making the state machine smarter might be a better option. | |
1604 | */ | |
1605 | #define RCU_IDLE_FLUSHES 5 /* Number of dyntick-idle tries. */ | |
1606 | #define RCU_IDLE_OPT_FLUSHES 3 /* Optional dyntick-idle tries. */ | |
e84c48ae | 1607 | #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */ |
778d250a | 1608 | #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */ |
f23f7fa1 | 1609 | |
9d2ad243 PM |
1610 | extern int tick_nohz_enabled; |
1611 | ||
486e2593 PM |
1612 | /* |
1613 | * Does the specified flavor of RCU have non-lazy callbacks pending on | |
1614 | * the specified CPU? Both RCU flavor and CPU are specified by the | |
1615 | * rcu_data structure. | |
1616 | */ | |
1617 | static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp) | |
1618 | { | |
1619 | return rdp->qlen != rdp->qlen_lazy; | |
1620 | } | |
1621 | ||
1622 | #ifdef CONFIG_TREE_PREEMPT_RCU | |
1623 | ||
1624 | /* | |
1625 | * Are there non-lazy RCU-preempt callbacks? (There cannot be if there | |
1626 | * is no RCU-preempt in the kernel.) | |
1627 | */ | |
1628 | static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu) | |
1629 | { | |
1630 | struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); | |
1631 | ||
1632 | return __rcu_cpu_has_nonlazy_callbacks(rdp); | |
1633 | } | |
1634 | ||
1635 | #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ | |
1636 | ||
1637 | static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu) | |
1638 | { | |
1639 | return 0; | |
1640 | } | |
1641 | ||
1642 | #endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */ | |
1643 | ||
1644 | /* | |
1645 | * Does any flavor of RCU have non-lazy callbacks on the specified CPU? | |
1646 | */ | |
1647 | static bool rcu_cpu_has_nonlazy_callbacks(int cpu) | |
1648 | { | |
1649 | return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) || | |
1650 | __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) || | |
1651 | rcu_preempt_cpu_has_nonlazy_callbacks(cpu); | |
1652 | } | |
1653 | ||
aa9b1630 PM |
1654 | /* |
1655 | * Allow the CPU to enter dyntick-idle mode if either: (1) There are no | |
1656 | * callbacks on this CPU, (2) this CPU has not yet attempted to enter | |
1657 | * dyntick-idle mode, or (3) this CPU is in the process of attempting to | |
1658 | * enter dyntick-idle mode. Otherwise, if we have recently tried and failed | |
1659 | * to enter dyntick-idle mode, we refuse to try to enter it. After all, | |
1660 | * it is better to incur scheduling-clock interrupts than to spin | |
1661 | * continuously for the same time duration! | |
1662 | * | |
1663 | * The delta_jiffies argument is used to store the time when RCU is | |
1664 | * going to need the CPU again if it still has callbacks. The reason | |
1665 | * for this is that rcu_prepare_for_idle() might need to post a timer, | |
1666 | * but if so, it will do so after tick_nohz_stop_sched_tick() has set | |
1667 | * the wakeup time for this CPU. This means that RCU's timer can be | |
1668 | * delayed until the wakeup time, which defeats the purpose of posting | |
1669 | * a timer. | |
1670 | */ | |
1671 | int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) | |
1672 | { | |
1673 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); | |
1674 | ||
1675 | /* Flag a new idle sojourn to the idle-entry state machine. */ | |
1676 | rdtp->idle_first_pass = 1; | |
1677 | /* If no callbacks, RCU doesn't need the CPU. */ | |
1678 | if (!rcu_cpu_has_callbacks(cpu)) { | |
1679 | *delta_jiffies = ULONG_MAX; | |
1680 | return 0; | |
1681 | } | |
1682 | if (rdtp->dyntick_holdoff == jiffies) { | |
1683 | /* RCU recently tried and failed, so don't try again. */ | |
1684 | *delta_jiffies = 1; | |
1685 | return 1; | |
1686 | } | |
1687 | /* Set up for the possibility that RCU will post a timer. */ | |
e84c48ae PM |
1688 | if (rcu_cpu_has_nonlazy_callbacks(cpu)) { |
1689 | *delta_jiffies = round_up(RCU_IDLE_GP_DELAY + jiffies, | |
1690 | RCU_IDLE_GP_DELAY) - jiffies; | |
1691 | } else { | |
1692 | *delta_jiffies = jiffies + RCU_IDLE_LAZY_GP_DELAY; | |
1693 | *delta_jiffies = round_jiffies(*delta_jiffies) - jiffies; | |
1694 | } | |
aa9b1630 PM |
1695 | return 0; |
1696 | } | |
1697 | ||
21e52e15 PM |
1698 | /* |
1699 | * Handler for smp_call_function_single(). The only point of this | |
1700 | * handler is to wake the CPU up, so the handler does only tracing. | |
1701 | */ | |
1702 | void rcu_idle_demigrate(void *unused) | |
1703 | { | |
1704 | trace_rcu_prep_idle("Demigrate"); | |
1705 | } | |
1706 | ||
7cb92499 PM |
1707 | /* |
1708 | * Timer handler used to force CPU to start pushing its remaining RCU | |
1709 | * callbacks in the case where it entered dyntick-idle mode with callbacks | |
1710 | * pending. The hander doesn't really need to do anything because the | |
1711 | * real work is done upon re-entry to idle, or by the next scheduling-clock | |
1712 | * interrupt should idle not be re-entered. | |
21e52e15 PM |
1713 | * |
1714 | * One special case: the timer gets migrated without awakening the CPU | |
1715 | * on which the timer was scheduled on. In this case, we must wake up | |
1716 | * that CPU. We do so with smp_call_function_single(). | |
7cb92499 | 1717 | */ |
21e52e15 | 1718 | static void rcu_idle_gp_timer_func(unsigned long cpu_in) |
7cb92499 | 1719 | { |
21e52e15 PM |
1720 | int cpu = (int)cpu_in; |
1721 | ||
7cb92499 | 1722 | trace_rcu_prep_idle("Timer"); |
21e52e15 PM |
1723 | if (cpu != smp_processor_id()) |
1724 | smp_call_function_single(cpu, rcu_idle_demigrate, NULL, 0); | |
1725 | else | |
1726 | WARN_ON_ONCE(1); /* Getting here can hang the system... */ | |
7cb92499 PM |
1727 | } |
1728 | ||
1729 | /* | |
1730 | * Initialize the timer used to pull CPUs out of dyntick-idle mode. | |
1731 | */ | |
1732 | static void rcu_prepare_for_idle_init(int cpu) | |
1733 | { | |
5955f7ee PM |
1734 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
1735 | ||
1736 | rdtp->dyntick_holdoff = jiffies - 1; | |
1737 | setup_timer(&rdtp->idle_gp_timer, rcu_idle_gp_timer_func, cpu); | |
1738 | rdtp->idle_gp_timer_expires = jiffies - 1; | |
1739 | rdtp->idle_first_pass = 1; | |
7cb92499 PM |
1740 | } |
1741 | ||
1742 | /* | |
1743 | * Clean up for exit from idle. Because we are exiting from idle, there | |
5955f7ee | 1744 | * is no longer any point to ->idle_gp_timer, so cancel it. This will |
7cb92499 PM |
1745 | * do nothing if this timer is not active, so just cancel it unconditionally. |
1746 | */ | |
1747 | static void rcu_cleanup_after_idle(int cpu) | |
1748 | { | |
5955f7ee PM |
1749 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
1750 | ||
1751 | del_timer(&rdtp->idle_gp_timer); | |
2fdbb31b | 1752 | trace_rcu_prep_idle("Cleanup after idle"); |
9d2ad243 | 1753 | rdtp->tick_nohz_enabled_snap = ACCESS_ONCE(tick_nohz_enabled); |
7cb92499 PM |
1754 | } |
1755 | ||
aea1b35e PM |
1756 | /* |
1757 | * Check to see if any RCU-related work can be done by the current CPU, | |
1758 | * and if so, schedule a softirq to get it done. This function is part | |
1759 | * of the RCU implementation; it is -not- an exported member of the RCU API. | |
8bd93a2c | 1760 | * |
aea1b35e PM |
1761 | * The idea is for the current CPU to clear out all work required by the |
1762 | * RCU core for the current grace period, so that this CPU can be permitted | |
1763 | * to enter dyntick-idle mode. In some cases, it will need to be awakened | |
1764 | * at the end of the grace period by whatever CPU ends the grace period. | |
1765 | * This allows CPUs to go dyntick-idle more quickly, and to reduce the | |
1766 | * number of wakeups by a modest integer factor. | |
a47cd880 PM |
1767 | * |
1768 | * Because it is not legal to invoke rcu_process_callbacks() with irqs | |
1769 | * disabled, we do one pass of force_quiescent_state(), then do a | |
a46e0899 | 1770 | * invoke_rcu_core() to cause rcu_process_callbacks() to be invoked |
5955f7ee | 1771 | * later. The ->dyntick_drain field controls the sequencing. |
aea1b35e PM |
1772 | * |
1773 | * The caller must have disabled interrupts. | |
8bd93a2c | 1774 | */ |
aea1b35e | 1775 | static void rcu_prepare_for_idle(int cpu) |
8bd93a2c | 1776 | { |
f511fc62 | 1777 | struct timer_list *tp; |
5955f7ee | 1778 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
9d2ad243 PM |
1779 | int tne; |
1780 | ||
1781 | /* Handle nohz enablement switches conservatively. */ | |
1782 | tne = ACCESS_ONCE(tick_nohz_enabled); | |
1783 | if (tne != rdtp->tick_nohz_enabled_snap) { | |
1784 | if (rcu_cpu_has_callbacks(cpu)) | |
1785 | invoke_rcu_core(); /* force nohz to see update. */ | |
1786 | rdtp->tick_nohz_enabled_snap = tne; | |
1787 | return; | |
1788 | } | |
1789 | if (!tne) | |
1790 | return; | |
f511fc62 | 1791 | |
9a0c6fef PM |
1792 | /* Adaptive-tick mode, where usermode execution is idle to RCU. */ |
1793 | if (!is_idle_task(current)) { | |
1794 | rdtp->dyntick_holdoff = jiffies - 1; | |
1795 | if (rcu_cpu_has_nonlazy_callbacks(cpu)) { | |
1796 | trace_rcu_prep_idle("User dyntick with callbacks"); | |
1797 | rdtp->idle_gp_timer_expires = | |
1798 | round_up(jiffies + RCU_IDLE_GP_DELAY, | |
1799 | RCU_IDLE_GP_DELAY); | |
1800 | } else if (rcu_cpu_has_callbacks(cpu)) { | |
1801 | rdtp->idle_gp_timer_expires = | |
1802 | round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY); | |
1803 | trace_rcu_prep_idle("User dyntick with lazy callbacks"); | |
1804 | } else { | |
1805 | return; | |
1806 | } | |
1807 | tp = &rdtp->idle_gp_timer; | |
1808 | mod_timer_pinned(tp, rdtp->idle_gp_timer_expires); | |
1809 | return; | |
1810 | } | |
1811 | ||
c57afe80 PM |
1812 | /* |
1813 | * If this is an idle re-entry, for example, due to use of | |
1814 | * RCU_NONIDLE() or the new idle-loop tracing API within the idle | |
1815 | * loop, then don't take any state-machine actions, unless the | |
1816 | * momentary exit from idle queued additional non-lazy callbacks. | |
5955f7ee | 1817 | * Instead, repost the ->idle_gp_timer if this CPU has callbacks |
c57afe80 PM |
1818 | * pending. |
1819 | */ | |
5955f7ee PM |
1820 | if (!rdtp->idle_first_pass && |
1821 | (rdtp->nonlazy_posted == rdtp->nonlazy_posted_snap)) { | |
f511fc62 | 1822 | if (rcu_cpu_has_callbacks(cpu)) { |
5955f7ee PM |
1823 | tp = &rdtp->idle_gp_timer; |
1824 | mod_timer_pinned(tp, rdtp->idle_gp_timer_expires); | |
f511fc62 | 1825 | } |
c57afe80 PM |
1826 | return; |
1827 | } | |
5955f7ee PM |
1828 | rdtp->idle_first_pass = 0; |
1829 | rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted - 1; | |
c57afe80 | 1830 | |
3084f2f8 | 1831 | /* |
f535a607 PM |
1832 | * If there are no callbacks on this CPU, enter dyntick-idle mode. |
1833 | * Also reset state to avoid prejudicing later attempts. | |
3084f2f8 | 1834 | */ |
aea1b35e | 1835 | if (!rcu_cpu_has_callbacks(cpu)) { |
5955f7ee PM |
1836 | rdtp->dyntick_holdoff = jiffies - 1; |
1837 | rdtp->dyntick_drain = 0; | |
433cdddc | 1838 | trace_rcu_prep_idle("No callbacks"); |
aea1b35e | 1839 | return; |
77e38ed3 | 1840 | } |
3084f2f8 PM |
1841 | |
1842 | /* | |
1843 | * If in holdoff mode, just return. We will presumably have | |
1844 | * refrained from disabling the scheduling-clock tick. | |
1845 | */ | |
5955f7ee | 1846 | if (rdtp->dyntick_holdoff == jiffies) { |
433cdddc | 1847 | trace_rcu_prep_idle("In holdoff"); |
aea1b35e | 1848 | return; |
433cdddc | 1849 | } |
a47cd880 | 1850 | |
5955f7ee PM |
1851 | /* Check and update the ->dyntick_drain sequencing. */ |
1852 | if (rdtp->dyntick_drain <= 0) { | |
a47cd880 | 1853 | /* First time through, initialize the counter. */ |
5955f7ee PM |
1854 | rdtp->dyntick_drain = RCU_IDLE_FLUSHES; |
1855 | } else if (rdtp->dyntick_drain <= RCU_IDLE_OPT_FLUSHES && | |
c3ce910b PM |
1856 | !rcu_pending(cpu) && |
1857 | !local_softirq_pending()) { | |
7cb92499 | 1858 | /* Can we go dyntick-idle despite still having callbacks? */ |
5955f7ee PM |
1859 | rdtp->dyntick_drain = 0; |
1860 | rdtp->dyntick_holdoff = jiffies; | |
fd4b3526 PM |
1861 | if (rcu_cpu_has_nonlazy_callbacks(cpu)) { |
1862 | trace_rcu_prep_idle("Dyntick with callbacks"); | |
5955f7ee | 1863 | rdtp->idle_gp_timer_expires = |
e84c48ae PM |
1864 | round_up(jiffies + RCU_IDLE_GP_DELAY, |
1865 | RCU_IDLE_GP_DELAY); | |
fd4b3526 | 1866 | } else { |
5955f7ee | 1867 | rdtp->idle_gp_timer_expires = |
e84c48ae | 1868 | round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY); |
fd4b3526 PM |
1869 | trace_rcu_prep_idle("Dyntick with lazy callbacks"); |
1870 | } | |
5955f7ee PM |
1871 | tp = &rdtp->idle_gp_timer; |
1872 | mod_timer_pinned(tp, rdtp->idle_gp_timer_expires); | |
1873 | rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; | |
f23f7fa1 | 1874 | return; /* Nothing more to do immediately. */ |
5955f7ee | 1875 | } else if (--(rdtp->dyntick_drain) <= 0) { |
a47cd880 | 1876 | /* We have hit the limit, so time to give up. */ |
5955f7ee | 1877 | rdtp->dyntick_holdoff = jiffies; |
433cdddc | 1878 | trace_rcu_prep_idle("Begin holdoff"); |
aea1b35e PM |
1879 | invoke_rcu_core(); /* Force the CPU out of dyntick-idle. */ |
1880 | return; | |
a47cd880 PM |
1881 | } |
1882 | ||
aea1b35e PM |
1883 | /* |
1884 | * Do one step of pushing the remaining RCU callbacks through | |
1885 | * the RCU core state machine. | |
1886 | */ | |
1887 | #ifdef CONFIG_TREE_PREEMPT_RCU | |
1888 | if (per_cpu(rcu_preempt_data, cpu).nxtlist) { | |
1889 | rcu_preempt_qs(cpu); | |
4cdfc175 | 1890 | force_quiescent_state(&rcu_preempt_state); |
aea1b35e PM |
1891 | } |
1892 | #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */ | |
a47cd880 PM |
1893 | if (per_cpu(rcu_sched_data, cpu).nxtlist) { |
1894 | rcu_sched_qs(cpu); | |
4cdfc175 | 1895 | force_quiescent_state(&rcu_sched_state); |
a47cd880 PM |
1896 | } |
1897 | if (per_cpu(rcu_bh_data, cpu).nxtlist) { | |
1898 | rcu_bh_qs(cpu); | |
4cdfc175 | 1899 | force_quiescent_state(&rcu_bh_state); |
8bd93a2c PM |
1900 | } |
1901 | ||
433cdddc PM |
1902 | /* |
1903 | * If RCU callbacks are still pending, RCU still needs this CPU. | |
1904 | * So try forcing the callbacks through the grace period. | |
1905 | */ | |
3ad0decf | 1906 | if (rcu_cpu_has_callbacks(cpu)) { |
433cdddc | 1907 | trace_rcu_prep_idle("More callbacks"); |
a46e0899 | 1908 | invoke_rcu_core(); |
c701d5d9 | 1909 | } else { |
433cdddc | 1910 | trace_rcu_prep_idle("Callbacks drained"); |
c701d5d9 | 1911 | } |
8bd93a2c PM |
1912 | } |
1913 | ||
c57afe80 | 1914 | /* |
98248a0e PM |
1915 | * Keep a running count of the number of non-lazy callbacks posted |
1916 | * on this CPU. This running counter (which is never decremented) allows | |
1917 | * rcu_prepare_for_idle() to detect when something out of the idle loop | |
1918 | * posts a callback, even if an equal number of callbacks are invoked. | |
1919 | * Of course, callbacks should only be posted from within a trace event | |
1920 | * designed to be called from idle or from within RCU_NONIDLE(). | |
c57afe80 PM |
1921 | */ |
1922 | static void rcu_idle_count_callbacks_posted(void) | |
1923 | { | |
5955f7ee | 1924 | __this_cpu_add(rcu_dynticks.nonlazy_posted, 1); |
c57afe80 PM |
1925 | } |
1926 | ||
b626c1b6 PM |
1927 | /* |
1928 | * Data for flushing lazy RCU callbacks at OOM time. | |
1929 | */ | |
1930 | static atomic_t oom_callback_count; | |
1931 | static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq); | |
1932 | ||
1933 | /* | |
1934 | * RCU OOM callback -- decrement the outstanding count and deliver the | |
1935 | * wake-up if we are the last one. | |
1936 | */ | |
1937 | static void rcu_oom_callback(struct rcu_head *rhp) | |
1938 | { | |
1939 | if (atomic_dec_and_test(&oom_callback_count)) | |
1940 | wake_up(&oom_callback_wq); | |
1941 | } | |
1942 | ||
1943 | /* | |
1944 | * Post an rcu_oom_notify callback on the current CPU if it has at | |
1945 | * least one lazy callback. This will unnecessarily post callbacks | |
1946 | * to CPUs that already have a non-lazy callback at the end of their | |
1947 | * callback list, but this is an infrequent operation, so accept some | |
1948 | * extra overhead to keep things simple. | |
1949 | */ | |
1950 | static void rcu_oom_notify_cpu(void *unused) | |
1951 | { | |
1952 | struct rcu_state *rsp; | |
1953 | struct rcu_data *rdp; | |
1954 | ||
1955 | for_each_rcu_flavor(rsp) { | |
1956 | rdp = __this_cpu_ptr(rsp->rda); | |
1957 | if (rdp->qlen_lazy != 0) { | |
1958 | atomic_inc(&oom_callback_count); | |
1959 | rsp->call(&rdp->oom_head, rcu_oom_callback); | |
1960 | } | |
1961 | } | |
1962 | } | |
1963 | ||
1964 | /* | |
1965 | * If low on memory, ensure that each CPU has a non-lazy callback. | |
1966 | * This will wake up CPUs that have only lazy callbacks, in turn | |
1967 | * ensuring that they free up the corresponding memory in a timely manner. | |
1968 | * Because an uncertain amount of memory will be freed in some uncertain | |
1969 | * timeframe, we do not claim to have freed anything. | |
1970 | */ | |
1971 | static int rcu_oom_notify(struct notifier_block *self, | |
1972 | unsigned long notused, void *nfreed) | |
1973 | { | |
1974 | int cpu; | |
1975 | ||
1976 | /* Wait for callbacks from earlier instance to complete. */ | |
1977 | wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0); | |
1978 | ||
1979 | /* | |
1980 | * Prevent premature wakeup: ensure that all increments happen | |
1981 | * before there is a chance of the counter reaching zero. | |
1982 | */ | |
1983 | atomic_set(&oom_callback_count, 1); | |
1984 | ||
1985 | get_online_cpus(); | |
1986 | for_each_online_cpu(cpu) { | |
1987 | smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1); | |
1988 | cond_resched(); | |
1989 | } | |
1990 | put_online_cpus(); | |
1991 | ||
1992 | /* Unconditionally decrement: no need to wake ourselves up. */ | |
1993 | atomic_dec(&oom_callback_count); | |
1994 | ||
1995 | return NOTIFY_OK; | |
1996 | } | |
1997 | ||
1998 | static struct notifier_block rcu_oom_nb = { | |
1999 | .notifier_call = rcu_oom_notify | |
2000 | }; | |
2001 | ||
2002 | static int __init rcu_register_oom_notifier(void) | |
2003 | { | |
2004 | register_oom_notifier(&rcu_oom_nb); | |
2005 | return 0; | |
2006 | } | |
2007 | early_initcall(rcu_register_oom_notifier); | |
2008 | ||
8bd93a2c | 2009 | #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
a858af28 PM |
2010 | |
2011 | #ifdef CONFIG_RCU_CPU_STALL_INFO | |
2012 | ||
2013 | #ifdef CONFIG_RCU_FAST_NO_HZ | |
2014 | ||
2015 | static void print_cpu_stall_fast_no_hz(char *cp, int cpu) | |
2016 | { | |
5955f7ee PM |
2017 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
2018 | struct timer_list *tltp = &rdtp->idle_gp_timer; | |
86f343b5 | 2019 | char c; |
a858af28 | 2020 | |
86f343b5 PM |
2021 | c = rdtp->dyntick_holdoff == jiffies ? 'H' : '.'; |
2022 | if (timer_pending(tltp)) | |
2023 | sprintf(cp, "drain=%d %c timer=%lu", | |
2024 | rdtp->dyntick_drain, c, tltp->expires - jiffies); | |
2025 | else | |
2026 | sprintf(cp, "drain=%d %c timer not pending", | |
2027 | rdtp->dyntick_drain, c); | |
a858af28 PM |
2028 | } |
2029 | ||
2030 | #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ | |
2031 | ||
2032 | static void print_cpu_stall_fast_no_hz(char *cp, int cpu) | |
2033 | { | |
1c17e4d4 | 2034 | *cp = '\0'; |
a858af28 PM |
2035 | } |
2036 | ||
2037 | #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ | |
2038 | ||
2039 | /* Initiate the stall-info list. */ | |
2040 | static void print_cpu_stall_info_begin(void) | |
2041 | { | |
2042 | printk(KERN_CONT "\n"); | |
2043 | } | |
2044 | ||
2045 | /* | |
2046 | * Print out diagnostic information for the specified stalled CPU. | |
2047 | * | |
2048 | * If the specified CPU is aware of the current RCU grace period | |
2049 | * (flavor specified by rsp), then print the number of scheduling | |
2050 | * clock interrupts the CPU has taken during the time that it has | |
2051 | * been aware. Otherwise, print the number of RCU grace periods | |
2052 | * that this CPU is ignorant of, for example, "1" if the CPU was | |
2053 | * aware of the previous grace period. | |
2054 | * | |
2055 | * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. | |
2056 | */ | |
2057 | static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) | |
2058 | { | |
2059 | char fast_no_hz[72]; | |
2060 | struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); | |
2061 | struct rcu_dynticks *rdtp = rdp->dynticks; | |
2062 | char *ticks_title; | |
2063 | unsigned long ticks_value; | |
2064 | ||
2065 | if (rsp->gpnum == rdp->gpnum) { | |
2066 | ticks_title = "ticks this GP"; | |
2067 | ticks_value = rdp->ticks_this_gp; | |
2068 | } else { | |
2069 | ticks_title = "GPs behind"; | |
2070 | ticks_value = rsp->gpnum - rdp->gpnum; | |
2071 | } | |
2072 | print_cpu_stall_fast_no_hz(fast_no_hz, cpu); | |
2073 | printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d %s\n", | |
2074 | cpu, ticks_value, ticks_title, | |
2075 | atomic_read(&rdtp->dynticks) & 0xfff, | |
2076 | rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting, | |
2077 | fast_no_hz); | |
2078 | } | |
2079 | ||
2080 | /* Terminate the stall-info list. */ | |
2081 | static void print_cpu_stall_info_end(void) | |
2082 | { | |
2083 | printk(KERN_ERR "\t"); | |
2084 | } | |
2085 | ||
2086 | /* Zero ->ticks_this_gp for all flavors of RCU. */ | |
2087 | static void zero_cpu_stall_ticks(struct rcu_data *rdp) | |
2088 | { | |
2089 | rdp->ticks_this_gp = 0; | |
2090 | } | |
2091 | ||
2092 | /* Increment ->ticks_this_gp for all flavors of RCU. */ | |
2093 | static void increment_cpu_stall_ticks(void) | |
2094 | { | |
115f7a7c PM |
2095 | struct rcu_state *rsp; |
2096 | ||
2097 | for_each_rcu_flavor(rsp) | |
2098 | __this_cpu_ptr(rsp->rda)->ticks_this_gp++; | |
a858af28 PM |
2099 | } |
2100 | ||
2101 | #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ | |
2102 | ||
2103 | static void print_cpu_stall_info_begin(void) | |
2104 | { | |
2105 | printk(KERN_CONT " {"); | |
2106 | } | |
2107 | ||
2108 | static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) | |
2109 | { | |
2110 | printk(KERN_CONT " %d", cpu); | |
2111 | } | |
2112 | ||
2113 | static void print_cpu_stall_info_end(void) | |
2114 | { | |
2115 | printk(KERN_CONT "} "); | |
2116 | } | |
2117 | ||
2118 | static void zero_cpu_stall_ticks(struct rcu_data *rdp) | |
2119 | { | |
2120 | } | |
2121 | ||
2122 | static void increment_cpu_stall_ticks(void) | |
2123 | { | |
2124 | } | |
2125 | ||
2126 | #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */ | |
3fbfbf7a PM |
2127 | |
2128 | #ifdef CONFIG_RCU_NOCB_CPU | |
2129 | ||
2130 | /* | |
2131 | * Offload callback processing from the boot-time-specified set of CPUs | |
2132 | * specified by rcu_nocb_mask. For each CPU in the set, there is a | |
2133 | * kthread created that pulls the callbacks from the corresponding CPU, | |
2134 | * waits for a grace period to elapse, and invokes the callbacks. | |
2135 | * The no-CBs CPUs do a wake_up() on their kthread when they insert | |
2136 | * a callback into any empty list, unless the rcu_nocb_poll boot parameter | |
2137 | * has been specified, in which case each kthread actively polls its | |
2138 | * CPU. (Which isn't so great for energy efficiency, but which does | |
2139 | * reduce RCU's overhead on that CPU.) | |
2140 | * | |
2141 | * This is intended to be used in conjunction with Frederic Weisbecker's | |
2142 | * adaptive-idle work, which would seriously reduce OS jitter on CPUs | |
2143 | * running CPU-bound user-mode computations. | |
2144 | * | |
2145 | * Offloading of callback processing could also in theory be used as | |
2146 | * an energy-efficiency measure because CPUs with no RCU callbacks | |
2147 | * queued are more aggressive about entering dyntick-idle mode. | |
2148 | */ | |
2149 | ||
2150 | ||
2151 | /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */ | |
2152 | static int __init rcu_nocb_setup(char *str) | |
2153 | { | |
2154 | alloc_bootmem_cpumask_var(&rcu_nocb_mask); | |
2155 | have_rcu_nocb_mask = true; | |
2156 | cpulist_parse(str, rcu_nocb_mask); | |
2157 | return 1; | |
2158 | } | |
2159 | __setup("rcu_nocbs=", rcu_nocb_setup); | |
2160 | ||
1b0048a4 PG |
2161 | static int __init parse_rcu_nocb_poll(char *arg) |
2162 | { | |
2163 | rcu_nocb_poll = 1; | |
2164 | return 0; | |
2165 | } | |
2166 | early_param("rcu_nocb_poll", parse_rcu_nocb_poll); | |
2167 | ||
3fbfbf7a PM |
2168 | /* Is the specified CPU a no-CPUs CPU? */ |
2169 | static bool is_nocb_cpu(int cpu) | |
2170 | { | |
2171 | if (have_rcu_nocb_mask) | |
2172 | return cpumask_test_cpu(cpu, rcu_nocb_mask); | |
2173 | return false; | |
2174 | } | |
2175 | ||
2176 | /* | |
2177 | * Enqueue the specified string of rcu_head structures onto the specified | |
2178 | * CPU's no-CBs lists. The CPU is specified by rdp, the head of the | |
2179 | * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy | |
2180 | * counts are supplied by rhcount and rhcount_lazy. | |
2181 | * | |
2182 | * If warranted, also wake up the kthread servicing this CPUs queues. | |
2183 | */ | |
2184 | static void __call_rcu_nocb_enqueue(struct rcu_data *rdp, | |
2185 | struct rcu_head *rhp, | |
2186 | struct rcu_head **rhtp, | |
2187 | int rhcount, int rhcount_lazy) | |
2188 | { | |
2189 | int len; | |
2190 | struct rcu_head **old_rhpp; | |
2191 | struct task_struct *t; | |
2192 | ||
2193 | /* Enqueue the callback on the nocb list and update counts. */ | |
2194 | old_rhpp = xchg(&rdp->nocb_tail, rhtp); | |
2195 | ACCESS_ONCE(*old_rhpp) = rhp; | |
2196 | atomic_long_add(rhcount, &rdp->nocb_q_count); | |
2197 | atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy); | |
2198 | ||
2199 | /* If we are not being polled and there is a kthread, awaken it ... */ | |
2200 | t = ACCESS_ONCE(rdp->nocb_kthread); | |
2201 | if (rcu_nocb_poll | !t) | |
2202 | return; | |
2203 | len = atomic_long_read(&rdp->nocb_q_count); | |
2204 | if (old_rhpp == &rdp->nocb_head) { | |
2205 | wake_up(&rdp->nocb_wq); /* ... only if queue was empty ... */ | |
2206 | rdp->qlen_last_fqs_check = 0; | |
2207 | } else if (len > rdp->qlen_last_fqs_check + qhimark) { | |
2208 | wake_up_process(t); /* ... or if many callbacks queued. */ | |
2209 | rdp->qlen_last_fqs_check = LONG_MAX / 2; | |
2210 | } | |
2211 | return; | |
2212 | } | |
2213 | ||
2214 | /* | |
2215 | * This is a helper for __call_rcu(), which invokes this when the normal | |
2216 | * callback queue is inoperable. If this is not a no-CBs CPU, this | |
2217 | * function returns failure back to __call_rcu(), which can complain | |
2218 | * appropriately. | |
2219 | * | |
2220 | * Otherwise, this function queues the callback where the corresponding | |
2221 | * "rcuo" kthread can find it. | |
2222 | */ | |
2223 | static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, | |
2224 | bool lazy) | |
2225 | { | |
2226 | ||
2227 | if (!is_nocb_cpu(rdp->cpu)) | |
2228 | return 0; | |
2229 | __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy); | |
2230 | return 1; | |
2231 | } | |
2232 | ||
2233 | /* | |
2234 | * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is | |
2235 | * not a no-CBs CPU. | |
2236 | */ | |
2237 | static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, | |
2238 | struct rcu_data *rdp) | |
2239 | { | |
2240 | long ql = rsp->qlen; | |
2241 | long qll = rsp->qlen_lazy; | |
2242 | ||
2243 | /* If this is not a no-CBs CPU, tell the caller to do it the old way. */ | |
2244 | if (!is_nocb_cpu(smp_processor_id())) | |
2245 | return 0; | |
2246 | rsp->qlen = 0; | |
2247 | rsp->qlen_lazy = 0; | |
2248 | ||
2249 | /* First, enqueue the donelist, if any. This preserves CB ordering. */ | |
2250 | if (rsp->orphan_donelist != NULL) { | |
2251 | __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist, | |
2252 | rsp->orphan_donetail, ql, qll); | |
2253 | ql = qll = 0; | |
2254 | rsp->orphan_donelist = NULL; | |
2255 | rsp->orphan_donetail = &rsp->orphan_donelist; | |
2256 | } | |
2257 | if (rsp->orphan_nxtlist != NULL) { | |
2258 | __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist, | |
2259 | rsp->orphan_nxttail, ql, qll); | |
2260 | ql = qll = 0; | |
2261 | rsp->orphan_nxtlist = NULL; | |
2262 | rsp->orphan_nxttail = &rsp->orphan_nxtlist; | |
2263 | } | |
2264 | return 1; | |
2265 | } | |
2266 | ||
2267 | /* | |
2268 | * There must be at least one non-no-CBs CPU in operation at any given | |
2269 | * time, because no-CBs CPUs are not capable of initiating grace periods | |
2270 | * independently. This function therefore complains if the specified | |
2271 | * CPU is the last non-no-CBs CPU, allowing the CPU-hotplug system to | |
2272 | * avoid offlining the last such CPU. (Recursion is a wonderful thing, | |
2273 | * but you have to have a base case!) | |
2274 | */ | |
2275 | static bool nocb_cpu_expendable(int cpu) | |
2276 | { | |
2277 | cpumask_var_t non_nocb_cpus; | |
2278 | int ret; | |
2279 | ||
2280 | /* | |
2281 | * If there are no no-CB CPUs or if this CPU is not a no-CB CPU, | |
2282 | * then offlining this CPU is harmless. Let it happen. | |
2283 | */ | |
2284 | if (!have_rcu_nocb_mask || is_nocb_cpu(cpu)) | |
2285 | return 1; | |
2286 | ||
2287 | /* If no memory, play it safe and keep the CPU around. */ | |
2288 | if (!alloc_cpumask_var(&non_nocb_cpus, GFP_NOIO)) | |
2289 | return 0; | |
2290 | cpumask_andnot(non_nocb_cpus, cpu_online_mask, rcu_nocb_mask); | |
2291 | cpumask_clear_cpu(cpu, non_nocb_cpus); | |
2292 | ret = !cpumask_empty(non_nocb_cpus); | |
2293 | free_cpumask_var(non_nocb_cpus); | |
2294 | return ret; | |
2295 | } | |
2296 | ||
2297 | /* | |
2298 | * Helper structure for remote registry of RCU callbacks. | |
2299 | * This is needed for when a no-CBs CPU needs to start a grace period. | |
2300 | * If it just invokes call_rcu(), the resulting callback will be queued, | |
2301 | * which can result in deadlock. | |
2302 | */ | |
2303 | struct rcu_head_remote { | |
2304 | struct rcu_head *rhp; | |
2305 | call_rcu_func_t *crf; | |
2306 | void (*func)(struct rcu_head *rhp); | |
2307 | }; | |
2308 | ||
2309 | /* | |
2310 | * Register a callback as specified by the rcu_head_remote struct. | |
2311 | * This function is intended to be invoked via smp_call_function_single(). | |
2312 | */ | |
2313 | static void call_rcu_local(void *arg) | |
2314 | { | |
2315 | struct rcu_head_remote *rhrp = | |
2316 | container_of(arg, struct rcu_head_remote, rhp); | |
2317 | ||
2318 | rhrp->crf(rhrp->rhp, rhrp->func); | |
2319 | } | |
2320 | ||
2321 | /* | |
2322 | * Set up an rcu_head_remote structure and the invoke call_rcu_local() | |
2323 | * on CPU 0 (which is guaranteed to be a non-no-CBs CPU) via | |
2324 | * smp_call_function_single(). | |
2325 | */ | |
2326 | static void invoke_crf_remote(struct rcu_head *rhp, | |
2327 | void (*func)(struct rcu_head *rhp), | |
2328 | call_rcu_func_t crf) | |
2329 | { | |
2330 | struct rcu_head_remote rhr; | |
2331 | ||
2332 | rhr.rhp = rhp; | |
2333 | rhr.crf = crf; | |
2334 | rhr.func = func; | |
2335 | smp_call_function_single(0, call_rcu_local, &rhr, 1); | |
2336 | } | |
2337 | ||
2338 | /* | |
2339 | * Helper functions to be passed to wait_rcu_gp(), each of which | |
2340 | * invokes invoke_crf_remote() to register a callback appropriately. | |
2341 | */ | |
2342 | static void __maybe_unused | |
2343 | call_rcu_preempt_remote(struct rcu_head *rhp, | |
2344 | void (*func)(struct rcu_head *rhp)) | |
2345 | { | |
2346 | invoke_crf_remote(rhp, func, call_rcu); | |
2347 | } | |
2348 | static void call_rcu_bh_remote(struct rcu_head *rhp, | |
2349 | void (*func)(struct rcu_head *rhp)) | |
2350 | { | |
2351 | invoke_crf_remote(rhp, func, call_rcu_bh); | |
2352 | } | |
2353 | static void call_rcu_sched_remote(struct rcu_head *rhp, | |
2354 | void (*func)(struct rcu_head *rhp)) | |
2355 | { | |
2356 | invoke_crf_remote(rhp, func, call_rcu_sched); | |
2357 | } | |
2358 | ||
2359 | /* | |
2360 | * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes | |
2361 | * callbacks queued by the corresponding no-CBs CPU. | |
2362 | */ | |
2363 | static int rcu_nocb_kthread(void *arg) | |
2364 | { | |
2365 | int c, cl; | |
2366 | struct rcu_head *list; | |
2367 | struct rcu_head *next; | |
2368 | struct rcu_head **tail; | |
2369 | struct rcu_data *rdp = arg; | |
2370 | ||
2371 | /* Each pass through this loop invokes one batch of callbacks */ | |
2372 | for (;;) { | |
2373 | /* If not polling, wait for next batch of callbacks. */ | |
2374 | if (!rcu_nocb_poll) | |
353af9c9 | 2375 | wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head); |
3fbfbf7a PM |
2376 | list = ACCESS_ONCE(rdp->nocb_head); |
2377 | if (!list) { | |
2378 | schedule_timeout_interruptible(1); | |
353af9c9 | 2379 | flush_signals(current); |
3fbfbf7a PM |
2380 | continue; |
2381 | } | |
2382 | ||
2383 | /* | |
2384 | * Extract queued callbacks, update counts, and wait | |
2385 | * for a grace period to elapse. | |
2386 | */ | |
2387 | ACCESS_ONCE(rdp->nocb_head) = NULL; | |
2388 | tail = xchg(&rdp->nocb_tail, &rdp->nocb_head); | |
2389 | c = atomic_long_xchg(&rdp->nocb_q_count, 0); | |
2390 | cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0); | |
2391 | ACCESS_ONCE(rdp->nocb_p_count) += c; | |
2392 | ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl; | |
2393 | wait_rcu_gp(rdp->rsp->call_remote); | |
2394 | ||
2395 | /* Each pass through the following loop invokes a callback. */ | |
2396 | trace_rcu_batch_start(rdp->rsp->name, cl, c, -1); | |
2397 | c = cl = 0; | |
2398 | while (list) { | |
2399 | next = list->next; | |
2400 | /* Wait for enqueuing to complete, if needed. */ | |
2401 | while (next == NULL && &list->next != tail) { | |
2402 | schedule_timeout_interruptible(1); | |
2403 | next = list->next; | |
2404 | } | |
2405 | debug_rcu_head_unqueue(list); | |
2406 | local_bh_disable(); | |
2407 | if (__rcu_reclaim(rdp->rsp->name, list)) | |
2408 | cl++; | |
2409 | c++; | |
2410 | local_bh_enable(); | |
2411 | list = next; | |
2412 | } | |
2413 | trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1); | |
2414 | ACCESS_ONCE(rdp->nocb_p_count) -= c; | |
2415 | ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl; | |
c635a4e1 | 2416 | rdp->n_nocbs_invoked += c; |
3fbfbf7a PM |
2417 | } |
2418 | return 0; | |
2419 | } | |
2420 | ||
2421 | /* Initialize per-rcu_data variables for no-CBs CPUs. */ | |
2422 | static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) | |
2423 | { | |
2424 | rdp->nocb_tail = &rdp->nocb_head; | |
2425 | init_waitqueue_head(&rdp->nocb_wq); | |
2426 | } | |
2427 | ||
2428 | /* Create a kthread for each RCU flavor for each no-CBs CPU. */ | |
2429 | static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp) | |
2430 | { | |
2431 | int cpu; | |
2432 | struct rcu_data *rdp; | |
2433 | struct task_struct *t; | |
2434 | ||
2435 | if (rcu_nocb_mask == NULL) | |
2436 | return; | |
2437 | for_each_cpu(cpu, rcu_nocb_mask) { | |
2438 | rdp = per_cpu_ptr(rsp->rda, cpu); | |
2439 | t = kthread_run(rcu_nocb_kthread, rdp, "rcuo%d", cpu); | |
2440 | BUG_ON(IS_ERR(t)); | |
2441 | ACCESS_ONCE(rdp->nocb_kthread) = t; | |
2442 | } | |
2443 | } | |
2444 | ||
2445 | /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */ | |
2446 | static void init_nocb_callback_list(struct rcu_data *rdp) | |
2447 | { | |
2448 | if (rcu_nocb_mask == NULL || | |
2449 | !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask)) | |
2450 | return; | |
2451 | rdp->nxttail[RCU_NEXT_TAIL] = NULL; | |
2452 | } | |
2453 | ||
2454 | /* Initialize the ->call_remote fields in the rcu_state structures. */ | |
2455 | static void __init rcu_init_nocb(void) | |
2456 | { | |
2457 | #ifdef CONFIG_PREEMPT_RCU | |
2458 | rcu_preempt_state.call_remote = call_rcu_preempt_remote; | |
2459 | #endif /* #ifdef CONFIG_PREEMPT_RCU */ | |
2460 | rcu_bh_state.call_remote = call_rcu_bh_remote; | |
2461 | rcu_sched_state.call_remote = call_rcu_sched_remote; | |
2462 | } | |
2463 | ||
2464 | #else /* #ifdef CONFIG_RCU_NOCB_CPU */ | |
2465 | ||
2466 | static bool is_nocb_cpu(int cpu) | |
2467 | { | |
2468 | return false; | |
2469 | } | |
2470 | ||
2471 | static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, | |
2472 | bool lazy) | |
2473 | { | |
2474 | return 0; | |
2475 | } | |
2476 | ||
2477 | static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, | |
2478 | struct rcu_data *rdp) | |
2479 | { | |
2480 | return 0; | |
2481 | } | |
2482 | ||
2483 | static bool nocb_cpu_expendable(int cpu) | |
2484 | { | |
2485 | return 1; | |
2486 | } | |
2487 | ||
2488 | static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) | |
2489 | { | |
2490 | } | |
2491 | ||
2492 | static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp) | |
2493 | { | |
2494 | } | |
2495 | ||
2496 | static void init_nocb_callback_list(struct rcu_data *rdp) | |
2497 | { | |
2498 | } | |
2499 | ||
2500 | static void __init rcu_init_nocb(void) | |
2501 | { | |
2502 | } | |
2503 | ||
2504 | #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ |