Contents of /alx-src/tags/kernel26-2.6.12-alx-r9/kernel/rcupdate.c
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Wed Mar 4 11:03:09 2009 UTC (15 years, 6 months ago) by niro
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Wed Mar 4 11:03:09 2009 UTC (15 years, 6 months ago) by niro
File MIME type: text/plain
File size: 14379 byte(s)
Tag kernel26-2.6.12-alx-r9
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 | /** |
447 | * synchronize_rcu - wait until a grace period has elapsed. |
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. |
454 | * |
455 | * If your read-side code is not protected by rcu_read_lock(), do -not- |
456 | * use synchronize_rcu(). |
457 | */ |
458 | void synchronize_rcu(void) |
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 | |
470 | /* |
471 | * Deprecated, use synchronize_rcu() or synchronize_sched() instead. |
472 | */ |
473 | void synchronize_kernel(void) |
474 | { |
475 | synchronize_rcu(); |
476 | } |
477 | |
478 | module_param(maxbatch, int, 0); |
479 | EXPORT_SYMBOL(call_rcu); /* WARNING: GPL-only in April 2006. */ |
480 | EXPORT_SYMBOL(call_rcu_bh); /* WARNING: GPL-only in April 2006. */ |
481 | EXPORT_SYMBOL_GPL(synchronize_rcu); |
482 | EXPORT_SYMBOL(synchronize_kernel); /* WARNING: GPL-only in April 2006. */ |