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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> | |
c0dfb290 | 48 | #include <linux/rcuref.h> |
1da177e4 LT |
49 | #include <linux/cpu.h> |
50 | ||
51 | /* Definition for rcupdate control block. */ | |
52 | struct rcu_ctrlblk rcu_ctrlblk = | |
53 | { .cur = -300, .completed = -300 }; | |
54 | struct rcu_ctrlblk rcu_bh_ctrlblk = | |
55 | { .cur = -300, .completed = -300 }; | |
56 | ||
57 | /* Bookkeeping of the progress of the grace period */ | |
58 | struct rcu_state { | |
59 | spinlock_t lock; /* Guard this struct and writes to rcu_ctrlblk */ | |
60 | cpumask_t cpumask; /* CPUs that need to switch in order */ | |
61 | /* for current batch to proceed. */ | |
62 | }; | |
63 | ||
64 | static struct rcu_state rcu_state ____cacheline_maxaligned_in_smp = | |
65 | {.lock = SPIN_LOCK_UNLOCKED, .cpumask = CPU_MASK_NONE }; | |
66 | static struct rcu_state rcu_bh_state ____cacheline_maxaligned_in_smp = | |
67 | {.lock = SPIN_LOCK_UNLOCKED, .cpumask = CPU_MASK_NONE }; | |
68 | ||
69 | DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L }; | |
70 | DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L }; | |
71 | ||
72 | /* Fake initialization required by compiler */ | |
73 | static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL}; | |
2cc78eb5 | 74 | static int maxbatch = 10000; |
1da177e4 | 75 | |
c0dfb290 DS |
76 | #ifndef __HAVE_ARCH_CMPXCHG |
77 | /* | |
78 | * We use an array of spinlocks for the rcurefs -- similar to ones in sparc | |
79 | * 32 bit atomic_t implementations, and a hash function similar to that | |
80 | * for our refcounting needs. | |
81 | * Can't help multiprocessors which donot have cmpxchg :( | |
82 | */ | |
83 | ||
84 | spinlock_t __rcuref_hash[RCUREF_HASH_SIZE] = { | |
85 | [0 ... (RCUREF_HASH_SIZE-1)] = SPIN_LOCK_UNLOCKED | |
86 | }; | |
87 | #endif | |
88 | ||
1da177e4 LT |
89 | /** |
90 | * call_rcu - Queue an RCU callback for invocation after a grace period. | |
91 | * @head: structure to be used for queueing the RCU updates. | |
92 | * @func: actual update function to be invoked after the grace period | |
93 | * | |
94 | * The update function will be invoked some time after a full grace | |
95 | * period elapses, in other words after all currently executing RCU | |
96 | * read-side critical sections have completed. RCU read-side critical | |
97 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), | |
98 | * and may be nested. | |
99 | */ | |
100 | void fastcall call_rcu(struct rcu_head *head, | |
101 | void (*func)(struct rcu_head *rcu)) | |
102 | { | |
103 | unsigned long flags; | |
104 | struct rcu_data *rdp; | |
105 | ||
106 | head->func = func; | |
107 | head->next = NULL; | |
108 | local_irq_save(flags); | |
109 | rdp = &__get_cpu_var(rcu_data); | |
110 | *rdp->nxttail = head; | |
111 | rdp->nxttail = &head->next; | |
5ee832db ED |
112 | |
113 | if (unlikely(++rdp->count > 10000)) | |
114 | set_need_resched(); | |
115 | ||
1da177e4 LT |
116 | local_irq_restore(flags); |
117 | } | |
118 | ||
119 | /** | |
120 | * call_rcu_bh - Queue an RCU for invocation after a quicker grace period. | |
121 | * @head: structure to be used for queueing the RCU updates. | |
122 | * @func: actual update function to be invoked after the grace period | |
123 | * | |
124 | * The update function will be invoked some time after a full grace | |
125 | * period elapses, in other words after all currently executing RCU | |
126 | * read-side critical sections have completed. call_rcu_bh() assumes | |
127 | * that the read-side critical sections end on completion of a softirq | |
128 | * handler. This means that read-side critical sections in process | |
129 | * context must not be interrupted by softirqs. This interface is to be | |
130 | * used when most of the read-side critical sections are in softirq context. | |
131 | * RCU read-side critical sections are delimited by rcu_read_lock() and | |
132 | * rcu_read_unlock(), * if in interrupt context or rcu_read_lock_bh() | |
133 | * and rcu_read_unlock_bh(), if in process context. These may be nested. | |
134 | */ | |
135 | void fastcall call_rcu_bh(struct rcu_head *head, | |
136 | void (*func)(struct rcu_head *rcu)) | |
137 | { | |
138 | unsigned long flags; | |
139 | struct rcu_data *rdp; | |
140 | ||
141 | head->func = func; | |
142 | head->next = NULL; | |
143 | local_irq_save(flags); | |
144 | rdp = &__get_cpu_var(rcu_bh_data); | |
145 | *rdp->nxttail = head; | |
146 | rdp->nxttail = &head->next; | |
5ee832db ED |
147 | rdp->count++; |
148 | /* | |
149 | * Should we directly call rcu_do_batch() here ? | |
150 | * if (unlikely(rdp->count > 10000)) | |
151 | * rcu_do_batch(rdp); | |
152 | */ | |
1da177e4 LT |
153 | local_irq_restore(flags); |
154 | } | |
155 | ||
156 | /* | |
157 | * Invoke the completed RCU callbacks. They are expected to be in | |
158 | * a per-cpu list. | |
159 | */ | |
160 | static void rcu_do_batch(struct rcu_data *rdp) | |
161 | { | |
162 | struct rcu_head *next, *list; | |
163 | int count = 0; | |
164 | ||
165 | list = rdp->donelist; | |
166 | while (list) { | |
167 | next = rdp->donelist = list->next; | |
168 | list->func(list); | |
169 | list = next; | |
5ee832db | 170 | rdp->count--; |
1da177e4 LT |
171 | if (++count >= maxbatch) |
172 | break; | |
173 | } | |
174 | if (!rdp->donelist) | |
175 | rdp->donetail = &rdp->donelist; | |
176 | else | |
177 | tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu)); | |
178 | } | |
179 | ||
180 | /* | |
181 | * Grace period handling: | |
182 | * The grace period handling consists out of two steps: | |
183 | * - A new grace period is started. | |
184 | * This is done by rcu_start_batch. The start is not broadcasted to | |
185 | * all cpus, they must pick this up by comparing rcp->cur with | |
186 | * rdp->quiescbatch. All cpus are recorded in the | |
187 | * rcu_state.cpumask bitmap. | |
188 | * - All cpus must go through a quiescent state. | |
189 | * Since the start of the grace period is not broadcasted, at least two | |
190 | * calls to rcu_check_quiescent_state are required: | |
191 | * The first call just notices that a new grace period is running. The | |
192 | * following calls check if there was a quiescent state since the beginning | |
193 | * of the grace period. If so, it updates rcu_state.cpumask. If | |
194 | * the bitmap is empty, then the grace period is completed. | |
195 | * rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace | |
196 | * period (if necessary). | |
197 | */ | |
198 | /* | |
199 | * Register a new batch of callbacks, and start it up if there is currently no | |
200 | * active batch and the batch to be registered has not already occurred. | |
201 | * Caller must hold rcu_state.lock. | |
202 | */ | |
203 | static void rcu_start_batch(struct rcu_ctrlblk *rcp, struct rcu_state *rsp, | |
204 | int next_pending) | |
205 | { | |
206 | if (next_pending) | |
207 | rcp->next_pending = 1; | |
208 | ||
209 | if (rcp->next_pending && | |
210 | rcp->completed == rcp->cur) { | |
211 | /* Can't change, since spin lock held. */ | |
212 | cpus_andnot(rsp->cpumask, cpu_online_map, nohz_cpu_mask); | |
213 | ||
214 | rcp->next_pending = 0; | |
215 | /* next_pending == 0 must be visible in __rcu_process_callbacks() | |
216 | * before it can see new value of cur. | |
217 | */ | |
218 | smp_wmb(); | |
219 | rcp->cur++; | |
220 | } | |
221 | } | |
222 | ||
223 | /* | |
224 | * cpu went through a quiescent state since the beginning of the grace period. | |
225 | * Clear it from the cpu mask and complete the grace period if it was the last | |
226 | * cpu. Start another grace period if someone has further entries pending | |
227 | */ | |
228 | static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp, struct rcu_state *rsp) | |
229 | { | |
230 | cpu_clear(cpu, rsp->cpumask); | |
231 | if (cpus_empty(rsp->cpumask)) { | |
232 | /* batch completed ! */ | |
233 | rcp->completed = rcp->cur; | |
234 | rcu_start_batch(rcp, rsp, 0); | |
235 | } | |
236 | } | |
237 | ||
238 | /* | |
239 | * Check if the cpu has gone through a quiescent state (say context | |
240 | * switch). If so and if it already hasn't done so in this RCU | |
241 | * quiescent cycle, then indicate that it has done so. | |
242 | */ | |
243 | static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp, | |
244 | struct rcu_state *rsp, struct rcu_data *rdp) | |
245 | { | |
246 | if (rdp->quiescbatch != rcp->cur) { | |
247 | /* start new grace period: */ | |
248 | rdp->qs_pending = 1; | |
249 | rdp->passed_quiesc = 0; | |
250 | rdp->quiescbatch = rcp->cur; | |
251 | return; | |
252 | } | |
253 | ||
254 | /* Grace period already completed for this cpu? | |
255 | * qs_pending is checked instead of the actual bitmap to avoid | |
256 | * cacheline trashing. | |
257 | */ | |
258 | if (!rdp->qs_pending) | |
259 | return; | |
260 | ||
261 | /* | |
262 | * Was there a quiescent state since the beginning of the grace | |
263 | * period? If no, then exit and wait for the next call. | |
264 | */ | |
265 | if (!rdp->passed_quiesc) | |
266 | return; | |
267 | rdp->qs_pending = 0; | |
268 | ||
269 | spin_lock(&rsp->lock); | |
270 | /* | |
271 | * rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync | |
272 | * during cpu startup. Ignore the quiescent state. | |
273 | */ | |
274 | if (likely(rdp->quiescbatch == rcp->cur)) | |
275 | cpu_quiet(rdp->cpu, rcp, rsp); | |
276 | ||
277 | spin_unlock(&rsp->lock); | |
278 | } | |
279 | ||
280 | ||
281 | #ifdef CONFIG_HOTPLUG_CPU | |
282 | ||
283 | /* warning! helper for rcu_offline_cpu. do not use elsewhere without reviewing | |
284 | * locking requirements, the list it's pulling from has to belong to a cpu | |
285 | * which is dead and hence not processing interrupts. | |
286 | */ | |
287 | static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list, | |
288 | struct rcu_head **tail) | |
289 | { | |
290 | local_irq_disable(); | |
291 | *this_rdp->nxttail = list; | |
292 | if (list) | |
293 | this_rdp->nxttail = tail; | |
294 | local_irq_enable(); | |
295 | } | |
296 | ||
297 | static void __rcu_offline_cpu(struct rcu_data *this_rdp, | |
298 | struct rcu_ctrlblk *rcp, struct rcu_state *rsp, struct rcu_data *rdp) | |
299 | { | |
300 | /* if the cpu going offline owns the grace period | |
301 | * we can block indefinitely waiting for it, so flush | |
302 | * it here | |
303 | */ | |
304 | spin_lock_bh(&rsp->lock); | |
305 | if (rcp->cur != rcp->completed) | |
306 | cpu_quiet(rdp->cpu, rcp, rsp); | |
307 | spin_unlock_bh(&rsp->lock); | |
308 | rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail); | |
309 | rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail); | |
310 | ||
311 | } | |
312 | static void rcu_offline_cpu(int cpu) | |
313 | { | |
314 | struct rcu_data *this_rdp = &get_cpu_var(rcu_data); | |
315 | struct rcu_data *this_bh_rdp = &get_cpu_var(rcu_bh_data); | |
316 | ||
317 | __rcu_offline_cpu(this_rdp, &rcu_ctrlblk, &rcu_state, | |
318 | &per_cpu(rcu_data, cpu)); | |
319 | __rcu_offline_cpu(this_bh_rdp, &rcu_bh_ctrlblk, &rcu_bh_state, | |
320 | &per_cpu(rcu_bh_data, cpu)); | |
321 | put_cpu_var(rcu_data); | |
322 | put_cpu_var(rcu_bh_data); | |
323 | tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu); | |
324 | } | |
325 | ||
326 | #else | |
327 | ||
328 | static void rcu_offline_cpu(int cpu) | |
329 | { | |
330 | } | |
331 | ||
332 | #endif | |
333 | ||
334 | /* | |
335 | * This does the RCU processing work from tasklet context. | |
336 | */ | |
337 | static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp, | |
338 | struct rcu_state *rsp, struct rcu_data *rdp) | |
339 | { | |
340 | if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) { | |
341 | *rdp->donetail = rdp->curlist; | |
342 | rdp->donetail = rdp->curtail; | |
343 | rdp->curlist = NULL; | |
344 | rdp->curtail = &rdp->curlist; | |
345 | } | |
346 | ||
347 | local_irq_disable(); | |
348 | if (rdp->nxtlist && !rdp->curlist) { | |
349 | rdp->curlist = rdp->nxtlist; | |
350 | rdp->curtail = rdp->nxttail; | |
351 | rdp->nxtlist = NULL; | |
352 | rdp->nxttail = &rdp->nxtlist; | |
353 | local_irq_enable(); | |
354 | ||
355 | /* | |
356 | * start the next batch of callbacks | |
357 | */ | |
358 | ||
359 | /* determine batch number */ | |
360 | rdp->batch = rcp->cur + 1; | |
361 | /* see the comment and corresponding wmb() in | |
362 | * the rcu_start_batch() | |
363 | */ | |
364 | smp_rmb(); | |
365 | ||
366 | if (!rcp->next_pending) { | |
367 | /* and start it/schedule start if it's a new batch */ | |
368 | spin_lock(&rsp->lock); | |
369 | rcu_start_batch(rcp, rsp, 1); | |
370 | spin_unlock(&rsp->lock); | |
371 | } | |
372 | } else { | |
373 | local_irq_enable(); | |
374 | } | |
375 | rcu_check_quiescent_state(rcp, rsp, rdp); | |
376 | if (rdp->donelist) | |
377 | rcu_do_batch(rdp); | |
378 | } | |
379 | ||
380 | static void rcu_process_callbacks(unsigned long unused) | |
381 | { | |
382 | __rcu_process_callbacks(&rcu_ctrlblk, &rcu_state, | |
383 | &__get_cpu_var(rcu_data)); | |
384 | __rcu_process_callbacks(&rcu_bh_ctrlblk, &rcu_bh_state, | |
385 | &__get_cpu_var(rcu_bh_data)); | |
386 | } | |
387 | ||
388 | void rcu_check_callbacks(int cpu, int user) | |
389 | { | |
390 | if (user || | |
391 | (idle_cpu(cpu) && !in_softirq() && | |
392 | hardirq_count() <= (1 << HARDIRQ_SHIFT))) { | |
393 | rcu_qsctr_inc(cpu); | |
394 | rcu_bh_qsctr_inc(cpu); | |
395 | } else if (!in_softirq()) | |
396 | rcu_bh_qsctr_inc(cpu); | |
397 | tasklet_schedule(&per_cpu(rcu_tasklet, cpu)); | |
398 | } | |
399 | ||
400 | static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp, | |
401 | struct rcu_data *rdp) | |
402 | { | |
403 | memset(rdp, 0, sizeof(*rdp)); | |
404 | rdp->curtail = &rdp->curlist; | |
405 | rdp->nxttail = &rdp->nxtlist; | |
406 | rdp->donetail = &rdp->donelist; | |
407 | rdp->quiescbatch = rcp->completed; | |
408 | rdp->qs_pending = 0; | |
409 | rdp->cpu = cpu; | |
410 | } | |
411 | ||
412 | static void __devinit rcu_online_cpu(int cpu) | |
413 | { | |
414 | struct rcu_data *rdp = &per_cpu(rcu_data, cpu); | |
415 | struct rcu_data *bh_rdp = &per_cpu(rcu_bh_data, cpu); | |
416 | ||
417 | rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp); | |
418 | rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp); | |
419 | tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL); | |
420 | } | |
421 | ||
422 | static int __devinit rcu_cpu_notify(struct notifier_block *self, | |
423 | unsigned long action, void *hcpu) | |
424 | { | |
425 | long cpu = (long)hcpu; | |
426 | switch (action) { | |
427 | case CPU_UP_PREPARE: | |
428 | rcu_online_cpu(cpu); | |
429 | break; | |
430 | case CPU_DEAD: | |
431 | rcu_offline_cpu(cpu); | |
432 | break; | |
433 | default: | |
434 | break; | |
435 | } | |
436 | return NOTIFY_OK; | |
437 | } | |
438 | ||
439 | static struct notifier_block __devinitdata rcu_nb = { | |
440 | .notifier_call = rcu_cpu_notify, | |
441 | }; | |
442 | ||
443 | /* | |
444 | * Initializes rcu mechanism. Assumed to be called early. | |
445 | * That is before local timer(SMP) or jiffie timer (uniproc) is setup. | |
446 | * Note that rcu_qsctr and friends are implicitly | |
447 | * initialized due to the choice of ``0'' for RCU_CTR_INVALID. | |
448 | */ | |
449 | void __init rcu_init(void) | |
450 | { | |
451 | rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, | |
452 | (void *)(long)smp_processor_id()); | |
453 | /* Register notifier for non-boot CPUs */ | |
454 | register_cpu_notifier(&rcu_nb); | |
455 | } | |
456 | ||
457 | struct rcu_synchronize { | |
458 | struct rcu_head head; | |
459 | struct completion completion; | |
460 | }; | |
461 | ||
462 | /* Because of FASTCALL declaration of complete, we use this wrapper */ | |
463 | static void wakeme_after_rcu(struct rcu_head *head) | |
464 | { | |
465 | struct rcu_synchronize *rcu; | |
466 | ||
467 | rcu = container_of(head, struct rcu_synchronize, head); | |
468 | complete(&rcu->completion); | |
469 | } | |
470 | ||
471 | /** | |
9b06e818 | 472 | * synchronize_rcu - wait until a grace period has elapsed. |
1da177e4 LT |
473 | * |
474 | * Control will return to the caller some time after a full grace | |
475 | * period has elapsed, in other words after all currently executing RCU | |
476 | * read-side critical sections have completed. RCU read-side critical | |
477 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), | |
478 | * and may be nested. | |
9b06e818 PM |
479 | * |
480 | * If your read-side code is not protected by rcu_read_lock(), do -not- | |
481 | * use synchronize_rcu(). | |
1da177e4 | 482 | */ |
9b06e818 | 483 | void synchronize_rcu(void) |
1da177e4 LT |
484 | { |
485 | struct rcu_synchronize rcu; | |
486 | ||
487 | init_completion(&rcu.completion); | |
488 | /* Will wake me after RCU finished */ | |
489 | call_rcu(&rcu.head, wakeme_after_rcu); | |
490 | ||
491 | /* Wait for it */ | |
492 | wait_for_completion(&rcu.completion); | |
493 | } | |
494 | ||
9b06e818 PM |
495 | /* |
496 | * Deprecated, use synchronize_rcu() or synchronize_sched() instead. | |
497 | */ | |
498 | void synchronize_kernel(void) | |
499 | { | |
500 | synchronize_rcu(); | |
501 | } | |
502 | ||
1da177e4 | 503 | module_param(maxbatch, int, 0); |
66cf8f14 PM |
504 | EXPORT_SYMBOL(call_rcu); /* WARNING: GPL-only in April 2006. */ |
505 | EXPORT_SYMBOL(call_rcu_bh); /* WARNING: GPL-only in April 2006. */ | |
9b06e818 | 506 | EXPORT_SYMBOL_GPL(synchronize_rcu); |
66cf8f14 | 507 | EXPORT_SYMBOL(synchronize_kernel); /* WARNING: GPL-only in April 2006. */ |