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1da177e4 LT |
1 | /* |
2 | * Read-Copy Update mechanism for mutual exclusion | |
3 | * | |
4 | * This program is free software; you can redistribute it and/or modify | |
5 | * it under the terms of the GNU General Public License as published by | |
6 | * the Free Software Foundation; either version 2 of the License, or | |
7 | * (at your option) any later version. | |
8 | * | |
9 | * This program is distributed in the hope that it will be useful, | |
10 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
11 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
12 | * GNU General Public License for more details. | |
13 | * | |
14 | * You should have received a copy of the GNU General Public License | |
15 | * along with this program; if not, write to the Free Software | |
16 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. | |
17 | * | |
18 | * Copyright (C) IBM Corporation, 2001 | |
19 | * | |
20 | * Authors: Dipankar Sarma <dipankar@in.ibm.com> | |
21 | * Manfred Spraul <manfred@colorfullife.com> | |
22 | * | |
23 | * Based on the original work by Paul McKenney <paulmck@us.ibm.com> | |
24 | * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. | |
25 | * Papers: | |
26 | * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf | |
27 | * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) | |
28 | * | |
29 | * For detailed explanation of Read-Copy Update mechanism see - | |
30 | * http://lse.sourceforge.net/locking/rcupdate.html | |
31 | * | |
32 | */ | |
33 | #include <linux/types.h> | |
34 | #include <linux/kernel.h> | |
35 | #include <linux/init.h> | |
36 | #include <linux/spinlock.h> | |
37 | #include <linux/smp.h> | |
38 | #include <linux/interrupt.h> | |
39 | #include <linux/sched.h> | |
40 | #include <asm/atomic.h> | |
41 | #include <linux/bitops.h> | |
42 | #include <linux/module.h> | |
43 | #include <linux/completion.h> | |
44 | #include <linux/moduleparam.h> | |
45 | #include <linux/percpu.h> | |
46 | #include <linux/notifier.h> | |
47 | #include <linux/rcupdate.h> | |
48 | #include <linux/cpu.h> | |
49 | ||
50 | /* Definition for rcupdate control block. */ | |
51 | struct rcu_ctrlblk rcu_ctrlblk = | |
52 | { .cur = -300, .completed = -300 }; | |
53 | struct rcu_ctrlblk rcu_bh_ctrlblk = | |
54 | { .cur = -300, .completed = -300 }; | |
55 | ||
56 | /* Bookkeeping of the progress of the grace period */ | |
57 | struct rcu_state { | |
58 | spinlock_t lock; /* Guard this struct and writes to rcu_ctrlblk */ | |
59 | cpumask_t cpumask; /* CPUs that need to switch in order */ | |
60 | /* for current batch to proceed. */ | |
61 | }; | |
62 | ||
63 | static struct rcu_state rcu_state ____cacheline_maxaligned_in_smp = | |
64 | {.lock = SPIN_LOCK_UNLOCKED, .cpumask = CPU_MASK_NONE }; | |
65 | static struct rcu_state rcu_bh_state ____cacheline_maxaligned_in_smp = | |
66 | {.lock = SPIN_LOCK_UNLOCKED, .cpumask = CPU_MASK_NONE }; | |
67 | ||
68 | DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L }; | |
69 | DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L }; | |
70 | ||
71 | /* Fake initialization required by compiler */ | |
72 | static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL}; | |
73 | static int maxbatch = 10; | |
74 | ||
75 | /** | |
76 | * call_rcu - Queue an RCU callback for invocation after a grace period. | |
77 | * @head: structure to be used for queueing the RCU updates. | |
78 | * @func: actual update function to be invoked after the grace period | |
79 | * | |
80 | * The update function will be invoked some time after a full grace | |
81 | * period elapses, in other words after all currently executing RCU | |
82 | * read-side critical sections have completed. RCU read-side critical | |
83 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), | |
84 | * and may be nested. | |
85 | */ | |
86 | void fastcall call_rcu(struct rcu_head *head, | |
87 | void (*func)(struct rcu_head *rcu)) | |
88 | { | |
89 | unsigned long flags; | |
90 | struct rcu_data *rdp; | |
91 | ||
92 | head->func = func; | |
93 | head->next = NULL; | |
94 | local_irq_save(flags); | |
95 | rdp = &__get_cpu_var(rcu_data); | |
96 | *rdp->nxttail = head; | |
97 | rdp->nxttail = &head->next; | |
98 | local_irq_restore(flags); | |
99 | } | |
100 | ||
101 | /** | |
102 | * call_rcu_bh - Queue an RCU for invocation after a quicker grace period. | |
103 | * @head: structure to be used for queueing the RCU updates. | |
104 | * @func: actual update function to be invoked after the grace period | |
105 | * | |
106 | * The update function will be invoked some time after a full grace | |
107 | * period elapses, in other words after all currently executing RCU | |
108 | * read-side critical sections have completed. call_rcu_bh() assumes | |
109 | * that the read-side critical sections end on completion of a softirq | |
110 | * handler. This means that read-side critical sections in process | |
111 | * context must not be interrupted by softirqs. This interface is to be | |
112 | * used when most of the read-side critical sections are in softirq context. | |
113 | * RCU read-side critical sections are delimited by rcu_read_lock() and | |
114 | * rcu_read_unlock(), * if in interrupt context or rcu_read_lock_bh() | |
115 | * and rcu_read_unlock_bh(), if in process context. These may be nested. | |
116 | */ | |
117 | void fastcall call_rcu_bh(struct rcu_head *head, | |
118 | void (*func)(struct rcu_head *rcu)) | |
119 | { | |
120 | unsigned long flags; | |
121 | struct rcu_data *rdp; | |
122 | ||
123 | head->func = func; | |
124 | head->next = NULL; | |
125 | local_irq_save(flags); | |
126 | rdp = &__get_cpu_var(rcu_bh_data); | |
127 | *rdp->nxttail = head; | |
128 | rdp->nxttail = &head->next; | |
129 | local_irq_restore(flags); | |
130 | } | |
131 | ||
132 | /* | |
133 | * Invoke the completed RCU callbacks. They are expected to be in | |
134 | * a per-cpu list. | |
135 | */ | |
136 | static void rcu_do_batch(struct rcu_data *rdp) | |
137 | { | |
138 | struct rcu_head *next, *list; | |
139 | int count = 0; | |
140 | ||
141 | list = rdp->donelist; | |
142 | while (list) { | |
143 | next = rdp->donelist = list->next; | |
144 | list->func(list); | |
145 | list = next; | |
146 | if (++count >= maxbatch) | |
147 | break; | |
148 | } | |
149 | if (!rdp->donelist) | |
150 | rdp->donetail = &rdp->donelist; | |
151 | else | |
152 | tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu)); | |
153 | } | |
154 | ||
155 | /* | |
156 | * Grace period handling: | |
157 | * The grace period handling consists out of two steps: | |
158 | * - A new grace period is started. | |
159 | * This is done by rcu_start_batch. The start is not broadcasted to | |
160 | * all cpus, they must pick this up by comparing rcp->cur with | |
161 | * rdp->quiescbatch. All cpus are recorded in the | |
162 | * rcu_state.cpumask bitmap. | |
163 | * - All cpus must go through a quiescent state. | |
164 | * Since the start of the grace period is not broadcasted, at least two | |
165 | * calls to rcu_check_quiescent_state are required: | |
166 | * The first call just notices that a new grace period is running. The | |
167 | * following calls check if there was a quiescent state since the beginning | |
168 | * of the grace period. If so, it updates rcu_state.cpumask. If | |
169 | * the bitmap is empty, then the grace period is completed. | |
170 | * rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace | |
171 | * period (if necessary). | |
172 | */ | |
173 | /* | |
174 | * Register a new batch of callbacks, and start it up if there is currently no | |
175 | * active batch and the batch to be registered has not already occurred. | |
176 | * Caller must hold rcu_state.lock. | |
177 | */ | |
178 | static void rcu_start_batch(struct rcu_ctrlblk *rcp, struct rcu_state *rsp, | |
179 | int next_pending) | |
180 | { | |
181 | if (next_pending) | |
182 | rcp->next_pending = 1; | |
183 | ||
184 | if (rcp->next_pending && | |
185 | rcp->completed == rcp->cur) { | |
186 | /* Can't change, since spin lock held. */ | |
187 | cpus_andnot(rsp->cpumask, cpu_online_map, nohz_cpu_mask); | |
188 | ||
189 | rcp->next_pending = 0; | |
190 | /* next_pending == 0 must be visible in __rcu_process_callbacks() | |
191 | * before it can see new value of cur. | |
192 | */ | |
193 | smp_wmb(); | |
194 | rcp->cur++; | |
195 | } | |
196 | } | |
197 | ||
198 | /* | |
199 | * cpu went through a quiescent state since the beginning of the grace period. | |
200 | * Clear it from the cpu mask and complete the grace period if it was the last | |
201 | * cpu. Start another grace period if someone has further entries pending | |
202 | */ | |
203 | static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp, struct rcu_state *rsp) | |
204 | { | |
205 | cpu_clear(cpu, rsp->cpumask); | |
206 | if (cpus_empty(rsp->cpumask)) { | |
207 | /* batch completed ! */ | |
208 | rcp->completed = rcp->cur; | |
209 | rcu_start_batch(rcp, rsp, 0); | |
210 | } | |
211 | } | |
212 | ||
213 | /* | |
214 | * Check if the cpu has gone through a quiescent state (say context | |
215 | * switch). If so and if it already hasn't done so in this RCU | |
216 | * quiescent cycle, then indicate that it has done so. | |
217 | */ | |
218 | static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp, | |
219 | struct rcu_state *rsp, struct rcu_data *rdp) | |
220 | { | |
221 | if (rdp->quiescbatch != rcp->cur) { | |
222 | /* start new grace period: */ | |
223 | rdp->qs_pending = 1; | |
224 | rdp->passed_quiesc = 0; | |
225 | rdp->quiescbatch = rcp->cur; | |
226 | return; | |
227 | } | |
228 | ||
229 | /* Grace period already completed for this cpu? | |
230 | * qs_pending is checked instead of the actual bitmap to avoid | |
231 | * cacheline trashing. | |
232 | */ | |
233 | if (!rdp->qs_pending) | |
234 | return; | |
235 | ||
236 | /* | |
237 | * Was there a quiescent state since the beginning of the grace | |
238 | * period? If no, then exit and wait for the next call. | |
239 | */ | |
240 | if (!rdp->passed_quiesc) | |
241 | return; | |
242 | rdp->qs_pending = 0; | |
243 | ||
244 | spin_lock(&rsp->lock); | |
245 | /* | |
246 | * rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync | |
247 | * during cpu startup. Ignore the quiescent state. | |
248 | */ | |
249 | if (likely(rdp->quiescbatch == rcp->cur)) | |
250 | cpu_quiet(rdp->cpu, rcp, rsp); | |
251 | ||
252 | spin_unlock(&rsp->lock); | |
253 | } | |
254 | ||
255 | ||
256 | #ifdef CONFIG_HOTPLUG_CPU | |
257 | ||
258 | /* warning! helper for rcu_offline_cpu. do not use elsewhere without reviewing | |
259 | * locking requirements, the list it's pulling from has to belong to a cpu | |
260 | * which is dead and hence not processing interrupts. | |
261 | */ | |
262 | static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list, | |
263 | struct rcu_head **tail) | |
264 | { | |
265 | local_irq_disable(); | |
266 | *this_rdp->nxttail = list; | |
267 | if (list) | |
268 | this_rdp->nxttail = tail; | |
269 | local_irq_enable(); | |
270 | } | |
271 | ||
272 | static void __rcu_offline_cpu(struct rcu_data *this_rdp, | |
273 | struct rcu_ctrlblk *rcp, struct rcu_state *rsp, struct rcu_data *rdp) | |
274 | { | |
275 | /* if the cpu going offline owns the grace period | |
276 | * we can block indefinitely waiting for it, so flush | |
277 | * it here | |
278 | */ | |
279 | spin_lock_bh(&rsp->lock); | |
280 | if (rcp->cur != rcp->completed) | |
281 | cpu_quiet(rdp->cpu, rcp, rsp); | |
282 | spin_unlock_bh(&rsp->lock); | |
283 | rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail); | |
284 | rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail); | |
285 | ||
286 | } | |
287 | static void rcu_offline_cpu(int cpu) | |
288 | { | |
289 | struct rcu_data *this_rdp = &get_cpu_var(rcu_data); | |
290 | struct rcu_data *this_bh_rdp = &get_cpu_var(rcu_bh_data); | |
291 | ||
292 | __rcu_offline_cpu(this_rdp, &rcu_ctrlblk, &rcu_state, | |
293 | &per_cpu(rcu_data, cpu)); | |
294 | __rcu_offline_cpu(this_bh_rdp, &rcu_bh_ctrlblk, &rcu_bh_state, | |
295 | &per_cpu(rcu_bh_data, cpu)); | |
296 | put_cpu_var(rcu_data); | |
297 | put_cpu_var(rcu_bh_data); | |
298 | tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu); | |
299 | } | |
300 | ||
301 | #else | |
302 | ||
303 | static void rcu_offline_cpu(int cpu) | |
304 | { | |
305 | } | |
306 | ||
307 | #endif | |
308 | ||
309 | /* | |
310 | * This does the RCU processing work from tasklet context. | |
311 | */ | |
312 | static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp, | |
313 | struct rcu_state *rsp, struct rcu_data *rdp) | |
314 | { | |
315 | if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) { | |
316 | *rdp->donetail = rdp->curlist; | |
317 | rdp->donetail = rdp->curtail; | |
318 | rdp->curlist = NULL; | |
319 | rdp->curtail = &rdp->curlist; | |
320 | } | |
321 | ||
322 | local_irq_disable(); | |
323 | if (rdp->nxtlist && !rdp->curlist) { | |
324 | rdp->curlist = rdp->nxtlist; | |
325 | rdp->curtail = rdp->nxttail; | |
326 | rdp->nxtlist = NULL; | |
327 | rdp->nxttail = &rdp->nxtlist; | |
328 | local_irq_enable(); | |
329 | ||
330 | /* | |
331 | * start the next batch of callbacks | |
332 | */ | |
333 | ||
334 | /* determine batch number */ | |
335 | rdp->batch = rcp->cur + 1; | |
336 | /* see the comment and corresponding wmb() in | |
337 | * the rcu_start_batch() | |
338 | */ | |
339 | smp_rmb(); | |
340 | ||
341 | if (!rcp->next_pending) { | |
342 | /* and start it/schedule start if it's a new batch */ | |
343 | spin_lock(&rsp->lock); | |
344 | rcu_start_batch(rcp, rsp, 1); | |
345 | spin_unlock(&rsp->lock); | |
346 | } | |
347 | } else { | |
348 | local_irq_enable(); | |
349 | } | |
350 | rcu_check_quiescent_state(rcp, rsp, rdp); | |
351 | if (rdp->donelist) | |
352 | rcu_do_batch(rdp); | |
353 | } | |
354 | ||
355 | static void rcu_process_callbacks(unsigned long unused) | |
356 | { | |
357 | __rcu_process_callbacks(&rcu_ctrlblk, &rcu_state, | |
358 | &__get_cpu_var(rcu_data)); | |
359 | __rcu_process_callbacks(&rcu_bh_ctrlblk, &rcu_bh_state, | |
360 | &__get_cpu_var(rcu_bh_data)); | |
361 | } | |
362 | ||
363 | void rcu_check_callbacks(int cpu, int user) | |
364 | { | |
365 | if (user || | |
366 | (idle_cpu(cpu) && !in_softirq() && | |
367 | hardirq_count() <= (1 << HARDIRQ_SHIFT))) { | |
368 | rcu_qsctr_inc(cpu); | |
369 | rcu_bh_qsctr_inc(cpu); | |
370 | } else if (!in_softirq()) | |
371 | rcu_bh_qsctr_inc(cpu); | |
372 | tasklet_schedule(&per_cpu(rcu_tasklet, cpu)); | |
373 | } | |
374 | ||
375 | static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp, | |
376 | struct rcu_data *rdp) | |
377 | { | |
378 | memset(rdp, 0, sizeof(*rdp)); | |
379 | rdp->curtail = &rdp->curlist; | |
380 | rdp->nxttail = &rdp->nxtlist; | |
381 | rdp->donetail = &rdp->donelist; | |
382 | rdp->quiescbatch = rcp->completed; | |
383 | rdp->qs_pending = 0; | |
384 | rdp->cpu = cpu; | |
385 | } | |
386 | ||
387 | static void __devinit rcu_online_cpu(int cpu) | |
388 | { | |
389 | struct rcu_data *rdp = &per_cpu(rcu_data, cpu); | |
390 | struct rcu_data *bh_rdp = &per_cpu(rcu_bh_data, cpu); | |
391 | ||
392 | rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp); | |
393 | rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp); | |
394 | tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL); | |
395 | } | |
396 | ||
397 | static int __devinit rcu_cpu_notify(struct notifier_block *self, | |
398 | unsigned long action, void *hcpu) | |
399 | { | |
400 | long cpu = (long)hcpu; | |
401 | switch (action) { | |
402 | case CPU_UP_PREPARE: | |
403 | rcu_online_cpu(cpu); | |
404 | break; | |
405 | case CPU_DEAD: | |
406 | rcu_offline_cpu(cpu); | |
407 | break; | |
408 | default: | |
409 | break; | |
410 | } | |
411 | return NOTIFY_OK; | |
412 | } | |
413 | ||
414 | static struct notifier_block __devinitdata rcu_nb = { | |
415 | .notifier_call = rcu_cpu_notify, | |
416 | }; | |
417 | ||
418 | /* | |
419 | * Initializes rcu mechanism. Assumed to be called early. | |
420 | * That is before local timer(SMP) or jiffie timer (uniproc) is setup. | |
421 | * Note that rcu_qsctr and friends are implicitly | |
422 | * initialized due to the choice of ``0'' for RCU_CTR_INVALID. | |
423 | */ | |
424 | void __init rcu_init(void) | |
425 | { | |
426 | rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, | |
427 | (void *)(long)smp_processor_id()); | |
428 | /* Register notifier for non-boot CPUs */ | |
429 | register_cpu_notifier(&rcu_nb); | |
430 | } | |
431 | ||
432 | struct rcu_synchronize { | |
433 | struct rcu_head head; | |
434 | struct completion completion; | |
435 | }; | |
436 | ||
437 | /* Because of FASTCALL declaration of complete, we use this wrapper */ | |
438 | static void wakeme_after_rcu(struct rcu_head *head) | |
439 | { | |
440 | struct rcu_synchronize *rcu; | |
441 | ||
442 | rcu = container_of(head, struct rcu_synchronize, head); | |
443 | complete(&rcu->completion); | |
444 | } | |
445 | ||
446 | /** | |
9b06e818 | 447 | * synchronize_rcu - wait until a grace period has elapsed. |
1da177e4 LT |
448 | * |
449 | * Control will return to the caller some time after a full grace | |
450 | * period has elapsed, in other words after all currently executing RCU | |
451 | * read-side critical sections have completed. RCU read-side critical | |
452 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), | |
453 | * and may be nested. | |
9b06e818 PM |
454 | * |
455 | * If your read-side code is not protected by rcu_read_lock(), do -not- | |
456 | * use synchronize_rcu(). | |
1da177e4 | 457 | */ |
9b06e818 | 458 | void synchronize_rcu(void) |
1da177e4 LT |
459 | { |
460 | struct rcu_synchronize rcu; | |
461 | ||
462 | init_completion(&rcu.completion); | |
463 | /* Will wake me after RCU finished */ | |
464 | call_rcu(&rcu.head, wakeme_after_rcu); | |
465 | ||
466 | /* Wait for it */ | |
467 | wait_for_completion(&rcu.completion); | |
468 | } | |
469 | ||
9b06e818 PM |
470 | /* |
471 | * Deprecated, use synchronize_rcu() or synchronize_sched() instead. | |
472 | */ | |
473 | void synchronize_kernel(void) | |
474 | { | |
475 | synchronize_rcu(); | |
476 | } | |
477 | ||
1da177e4 | 478 | module_param(maxbatch, int, 0); |
66cf8f14 PM |
479 | EXPORT_SYMBOL(call_rcu); /* WARNING: GPL-only in April 2006. */ |
480 | EXPORT_SYMBOL(call_rcu_bh); /* WARNING: GPL-only in April 2006. */ | |
9b06e818 | 481 | EXPORT_SYMBOL_GPL(synchronize_rcu); |
66cf8f14 | 482 | EXPORT_SYMBOL(synchronize_kernel); /* WARNING: GPL-only in April 2006. */ |