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-rw-r--r--kernel/slow-work.c1068
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diff --git a/kernel/slow-work.c b/kernel/slow-work.c
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1/* Worker thread pool for slow items, such as filesystem lookups or mkdirs
2 *
3 * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
4 * Written by David Howells (dhowells@redhat.com)
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public Licence
8 * as published by the Free Software Foundation; either version
9 * 2 of the Licence, or (at your option) any later version.
10 *
11 * See Documentation/slow-work.txt
12 */
13
14#include <linux/module.h>
15#include <linux/slow-work.h>
16#include <linux/kthread.h>
17#include <linux/freezer.h>
18#include <linux/wait.h>
19#include <linux/debugfs.h>
20#include "slow-work.h"
21
22static void slow_work_cull_timeout(unsigned long);
23static void slow_work_oom_timeout(unsigned long);
24
25#ifdef CONFIG_SYSCTL
26static int slow_work_min_threads_sysctl(struct ctl_table *, int,
27 void __user *, size_t *, loff_t *);
28
29static int slow_work_max_threads_sysctl(struct ctl_table *, int ,
30 void __user *, size_t *, loff_t *);
31#endif
32
33/*
34 * The pool of threads has at least min threads in it as long as someone is
35 * using the facility, and may have as many as max.
36 *
37 * A portion of the pool may be processing very slow operations.
38 */
39static unsigned slow_work_min_threads = 2;
40static unsigned slow_work_max_threads = 4;
41static unsigned vslow_work_proportion = 50; /* % of threads that may process
42 * very slow work */
43
44#ifdef CONFIG_SYSCTL
45static const int slow_work_min_min_threads = 2;
46static int slow_work_max_max_threads = SLOW_WORK_THREAD_LIMIT;
47static const int slow_work_min_vslow = 1;
48static const int slow_work_max_vslow = 99;
49
50ctl_table slow_work_sysctls[] = {
51 {
52 .procname = "min-threads",
53 .data = &slow_work_min_threads,
54 .maxlen = sizeof(unsigned),
55 .mode = 0644,
56 .proc_handler = slow_work_min_threads_sysctl,
57 .extra1 = (void *) &slow_work_min_min_threads,
58 .extra2 = &slow_work_max_threads,
59 },
60 {
61 .procname = "max-threads",
62 .data = &slow_work_max_threads,
63 .maxlen = sizeof(unsigned),
64 .mode = 0644,
65 .proc_handler = slow_work_max_threads_sysctl,
66 .extra1 = &slow_work_min_threads,
67 .extra2 = (void *) &slow_work_max_max_threads,
68 },
69 {
70 .procname = "vslow-percentage",
71 .data = &vslow_work_proportion,
72 .maxlen = sizeof(unsigned),
73 .mode = 0644,
74 .proc_handler = proc_dointvec_minmax,
75 .extra1 = (void *) &slow_work_min_vslow,
76 .extra2 = (void *) &slow_work_max_vslow,
77 },
78 {}
79};
80#endif
81
82/*
83 * The active state of the thread pool
84 */
85static atomic_t slow_work_thread_count;
86static atomic_t vslow_work_executing_count;
87
88static bool slow_work_may_not_start_new_thread;
89static bool slow_work_cull; /* cull a thread due to lack of activity */
90static DEFINE_TIMER(slow_work_cull_timer, slow_work_cull_timeout, 0, 0);
91static DEFINE_TIMER(slow_work_oom_timer, slow_work_oom_timeout, 0, 0);
92static struct slow_work slow_work_new_thread; /* new thread starter */
93
94/*
95 * slow work ID allocation (use slow_work_queue_lock)
96 */
97static DECLARE_BITMAP(slow_work_ids, SLOW_WORK_THREAD_LIMIT);
98
99/*
100 * Unregistration tracking to prevent put_ref() from disappearing during module
101 * unload
102 */
103#ifdef CONFIG_MODULES
104static struct module *slow_work_thread_processing[SLOW_WORK_THREAD_LIMIT];
105static struct module *slow_work_unreg_module;
106static struct slow_work *slow_work_unreg_work_item;
107static DECLARE_WAIT_QUEUE_HEAD(slow_work_unreg_wq);
108static DEFINE_MUTEX(slow_work_unreg_sync_lock);
109
110static void slow_work_set_thread_processing(int id, struct slow_work *work)
111{
112 if (work)
113 slow_work_thread_processing[id] = work->owner;
114}
115static void slow_work_done_thread_processing(int id, struct slow_work *work)
116{
117 struct module *module = slow_work_thread_processing[id];
118
119 slow_work_thread_processing[id] = NULL;
120 smp_mb();
121 if (slow_work_unreg_work_item == work ||
122 slow_work_unreg_module == module)
123 wake_up_all(&slow_work_unreg_wq);
124}
125static void slow_work_clear_thread_processing(int id)
126{
127 slow_work_thread_processing[id] = NULL;
128}
129#else
130static void slow_work_set_thread_processing(int id, struct slow_work *work) {}
131static void slow_work_done_thread_processing(int id, struct slow_work *work) {}
132static void slow_work_clear_thread_processing(int id) {}
133#endif
134
135/*
136 * Data for tracking currently executing items for indication through /proc
137 */
138#ifdef CONFIG_SLOW_WORK_DEBUG
139struct slow_work *slow_work_execs[SLOW_WORK_THREAD_LIMIT];
140pid_t slow_work_pids[SLOW_WORK_THREAD_LIMIT];
141DEFINE_RWLOCK(slow_work_execs_lock);
142#endif
143
144/*
145 * The queues of work items and the lock governing access to them. These are
146 * shared between all the CPUs. It doesn't make sense to have per-CPU queues
147 * as the number of threads bears no relation to the number of CPUs.
148 *
149 * There are two queues of work items: one for slow work items, and one for
150 * very slow work items.
151 */
152LIST_HEAD(slow_work_queue);
153LIST_HEAD(vslow_work_queue);
154DEFINE_SPINLOCK(slow_work_queue_lock);
155
156/*
157 * The following are two wait queues that get pinged when a work item is placed
158 * on an empty queue. These allow work items that are hogging a thread by
159 * sleeping in a way that could be deferred to yield their thread and enqueue
160 * themselves.
161 */
162static DECLARE_WAIT_QUEUE_HEAD(slow_work_queue_waits_for_occupation);
163static DECLARE_WAIT_QUEUE_HEAD(vslow_work_queue_waits_for_occupation);
164
165/*
166 * The thread controls. A variable used to signal to the threads that they
167 * should exit when the queue is empty, a waitqueue used by the threads to wait
168 * for signals, and a completion set by the last thread to exit.
169 */
170static bool slow_work_threads_should_exit;
171static DECLARE_WAIT_QUEUE_HEAD(slow_work_thread_wq);
172static DECLARE_COMPLETION(slow_work_last_thread_exited);
173
174/*
175 * The number of users of the thread pool and its lock. Whilst this is zero we
176 * have no threads hanging around, and when this reaches zero, we wait for all
177 * active or queued work items to complete and kill all the threads we do have.
178 */
179static int slow_work_user_count;
180static DEFINE_MUTEX(slow_work_user_lock);
181
182static inline int slow_work_get_ref(struct slow_work *work)
183{
184 if (work->ops->get_ref)
185 return work->ops->get_ref(work);
186
187 return 0;
188}
189
190static inline void slow_work_put_ref(struct slow_work *work)
191{
192 if (work->ops->put_ref)
193 work->ops->put_ref(work);
194}
195
196/*
197 * Calculate the maximum number of active threads in the pool that are
198 * permitted to process very slow work items.
199 *
200 * The answer is rounded up to at least 1, but may not equal or exceed the
201 * maximum number of the threads in the pool. This means we always have at
202 * least one thread that can process slow work items, and we always have at
203 * least one thread that won't get tied up doing so.
204 */
205static unsigned slow_work_calc_vsmax(void)
206{
207 unsigned vsmax;
208
209 vsmax = atomic_read(&slow_work_thread_count) * vslow_work_proportion;
210 vsmax /= 100;
211 vsmax = max(vsmax, 1U);
212 return min(vsmax, slow_work_max_threads - 1);
213}
214
215/*
216 * Attempt to execute stuff queued on a slow thread. Return true if we managed
217 * it, false if there was nothing to do.
218 */
219static noinline bool slow_work_execute(int id)
220{
221 struct slow_work *work = NULL;
222 unsigned vsmax;
223 bool very_slow;
224
225 vsmax = slow_work_calc_vsmax();
226
227 /* see if we can schedule a new thread to be started if we're not
228 * keeping up with the work */
229 if (!waitqueue_active(&slow_work_thread_wq) &&
230 (!list_empty(&slow_work_queue) || !list_empty(&vslow_work_queue)) &&
231 atomic_read(&slow_work_thread_count) < slow_work_max_threads &&
232 !slow_work_may_not_start_new_thread)
233 slow_work_enqueue(&slow_work_new_thread);
234
235 /* find something to execute */
236 spin_lock_irq(&slow_work_queue_lock);
237 if (!list_empty(&vslow_work_queue) &&
238 atomic_read(&vslow_work_executing_count) < vsmax) {
239 work = list_entry(vslow_work_queue.next,
240 struct slow_work, link);
241 if (test_and_set_bit_lock(SLOW_WORK_EXECUTING, &work->flags))
242 BUG();
243 list_del_init(&work->link);
244 atomic_inc(&vslow_work_executing_count);
245 very_slow = true;
246 } else if (!list_empty(&slow_work_queue)) {
247 work = list_entry(slow_work_queue.next,
248 struct slow_work, link);
249 if (test_and_set_bit_lock(SLOW_WORK_EXECUTING, &work->flags))
250 BUG();
251 list_del_init(&work->link);
252 very_slow = false;
253 } else {
254 very_slow = false; /* avoid the compiler warning */
255 }
256
257 slow_work_set_thread_processing(id, work);
258 if (work) {
259 slow_work_mark_time(work);
260 slow_work_begin_exec(id, work);
261 }
262
263 spin_unlock_irq(&slow_work_queue_lock);
264
265 if (!work)
266 return false;
267
268 if (!test_and_clear_bit(SLOW_WORK_PENDING, &work->flags))
269 BUG();
270
271 /* don't execute if the work is in the process of being cancelled */
272 if (!test_bit(SLOW_WORK_CANCELLING, &work->flags))
273 work->ops->execute(work);
274
275 if (very_slow)
276 atomic_dec(&vslow_work_executing_count);
277 clear_bit_unlock(SLOW_WORK_EXECUTING, &work->flags);
278
279 /* wake up anyone waiting for this work to be complete */
280 wake_up_bit(&work->flags, SLOW_WORK_EXECUTING);
281
282 slow_work_end_exec(id, work);
283
284 /* if someone tried to enqueue the item whilst we were executing it,
285 * then it'll be left unenqueued to avoid multiple threads trying to
286 * execute it simultaneously
287 *
288 * there is, however, a race between us testing the pending flag and
289 * getting the spinlock, and between the enqueuer setting the pending
290 * flag and getting the spinlock, so we use a deferral bit to tell us
291 * if the enqueuer got there first
292 */
293 if (test_bit(SLOW_WORK_PENDING, &work->flags)) {
294 spin_lock_irq(&slow_work_queue_lock);
295
296 if (!test_bit(SLOW_WORK_EXECUTING, &work->flags) &&
297 test_and_clear_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags))
298 goto auto_requeue;
299
300 spin_unlock_irq(&slow_work_queue_lock);
301 }
302
303 /* sort out the race between module unloading and put_ref() */
304 slow_work_put_ref(work);
305 slow_work_done_thread_processing(id, work);
306
307 return true;
308
309auto_requeue:
310 /* we must complete the enqueue operation
311 * - we transfer our ref on the item back to the appropriate queue
312 * - don't wake another thread up as we're awake already
313 */
314 slow_work_mark_time(work);
315 if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags))
316 list_add_tail(&work->link, &vslow_work_queue);
317 else
318 list_add_tail(&work->link, &slow_work_queue);
319 spin_unlock_irq(&slow_work_queue_lock);
320 slow_work_clear_thread_processing(id);
321 return true;
322}
323
324/**
325 * slow_work_sleep_till_thread_needed - Sleep till thread needed by other work
326 * work: The work item under execution that wants to sleep
327 * _timeout: Scheduler sleep timeout
328 *
329 * Allow a requeueable work item to sleep on a slow-work processor thread until
330 * that thread is needed to do some other work or the sleep is interrupted by
331 * some other event.
332 *
333 * The caller must set up a wake up event before calling this and must have set
334 * the appropriate sleep mode (such as TASK_UNINTERRUPTIBLE) and tested its own
335 * condition before calling this function as no test is made here.
336 *
337 * False is returned if there is nothing on the queue; true is returned if the
338 * work item should be requeued
339 */
340bool slow_work_sleep_till_thread_needed(struct slow_work *work,
341 signed long *_timeout)
342{
343 wait_queue_head_t *wfo_wq;
344 struct list_head *queue;
345
346 DEFINE_WAIT(wait);
347
348 if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {
349 wfo_wq = &vslow_work_queue_waits_for_occupation;
350 queue = &vslow_work_queue;
351 } else {
352 wfo_wq = &slow_work_queue_waits_for_occupation;
353 queue = &slow_work_queue;
354 }
355
356 if (!list_empty(queue))
357 return true;
358
359 add_wait_queue_exclusive(wfo_wq, &wait);
360 if (list_empty(queue))
361 *_timeout = schedule_timeout(*_timeout);
362 finish_wait(wfo_wq, &wait);
363
364 return !list_empty(queue);
365}
366EXPORT_SYMBOL(slow_work_sleep_till_thread_needed);
367
368/**
369 * slow_work_enqueue - Schedule a slow work item for processing
370 * @work: The work item to queue
371 *
372 * Schedule a slow work item for processing. If the item is already undergoing
373 * execution, this guarantees not to re-enter the execution routine until the
374 * first execution finishes.
375 *
376 * The item is pinned by this function as it retains a reference to it, managed
377 * through the item operations. The item is unpinned once it has been
378 * executed.
379 *
380 * An item may hog the thread that is running it for a relatively large amount
381 * of time, sufficient, for example, to perform several lookup, mkdir, create
382 * and setxattr operations. It may sleep on I/O and may sleep to obtain locks.
383 *
384 * Conversely, if a number of items are awaiting processing, it may take some
385 * time before any given item is given attention. The number of threads in the
386 * pool may be increased to deal with demand, but only up to a limit.
387 *
388 * If SLOW_WORK_VERY_SLOW is set on the work item, then it will be placed in
389 * the very slow queue, from which only a portion of the threads will be
390 * allowed to pick items to execute. This ensures that very slow items won't
391 * overly block ones that are just ordinarily slow.
392 *
393 * Returns 0 if successful, -EAGAIN if not (or -ECANCELED if cancelled work is
394 * attempted queued)
395 */
396int slow_work_enqueue(struct slow_work *work)
397{
398 wait_queue_head_t *wfo_wq;
399 struct list_head *queue;
400 unsigned long flags;
401 int ret;
402
403 if (test_bit(SLOW_WORK_CANCELLING, &work->flags))
404 return -ECANCELED;
405
406 BUG_ON(slow_work_user_count <= 0);
407 BUG_ON(!work);
408 BUG_ON(!work->ops);
409
410 /* when honouring an enqueue request, we only promise that we will run
411 * the work function in the future; we do not promise to run it once
412 * per enqueue request
413 *
414 * we use the PENDING bit to merge together repeat requests without
415 * having to disable IRQs and take the spinlock, whilst still
416 * maintaining our promise
417 */
418 if (!test_and_set_bit_lock(SLOW_WORK_PENDING, &work->flags)) {
419 if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {
420 wfo_wq = &vslow_work_queue_waits_for_occupation;
421 queue = &vslow_work_queue;
422 } else {
423 wfo_wq = &slow_work_queue_waits_for_occupation;
424 queue = &slow_work_queue;
425 }
426
427 spin_lock_irqsave(&slow_work_queue_lock, flags);
428
429 if (unlikely(test_bit(SLOW_WORK_CANCELLING, &work->flags)))
430 goto cancelled;
431
432 /* we promise that we will not attempt to execute the work
433 * function in more than one thread simultaneously
434 *
435 * this, however, leaves us with a problem if we're asked to
436 * enqueue the work whilst someone is executing the work
437 * function as simply queueing the work immediately means that
438 * another thread may try executing it whilst it is already
439 * under execution
440 *
441 * to deal with this, we set the ENQ_DEFERRED bit instead of
442 * enqueueing, and the thread currently executing the work
443 * function will enqueue the work item when the work function
444 * returns and it has cleared the EXECUTING bit
445 */
446 if (test_bit(SLOW_WORK_EXECUTING, &work->flags)) {
447 set_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags);
448 } else {
449 ret = slow_work_get_ref(work);
450 if (ret < 0)
451 goto failed;
452 slow_work_mark_time(work);
453 list_add_tail(&work->link, queue);
454 wake_up(&slow_work_thread_wq);
455
456 /* if someone who could be requeued is sleeping on a
457 * thread, then ask them to yield their thread */
458 if (work->link.prev == queue)
459 wake_up(wfo_wq);
460 }
461
462 spin_unlock_irqrestore(&slow_work_queue_lock, flags);
463 }
464 return 0;
465
466cancelled:
467 ret = -ECANCELED;
468failed:
469 spin_unlock_irqrestore(&slow_work_queue_lock, flags);
470 return ret;
471}
472EXPORT_SYMBOL(slow_work_enqueue);
473
474static int slow_work_wait(void *word)
475{
476 schedule();
477 return 0;
478}
479
480/**
481 * slow_work_cancel - Cancel a slow work item
482 * @work: The work item to cancel
483 *
484 * This function will cancel a previously enqueued work item. If we cannot
485 * cancel the work item, it is guarenteed to have run when this function
486 * returns.
487 */
488void slow_work_cancel(struct slow_work *work)
489{
490 bool wait = true, put = false;
491
492 set_bit(SLOW_WORK_CANCELLING, &work->flags);
493 smp_mb();
494
495 /* if the work item is a delayed work item with an active timer, we
496 * need to wait for the timer to finish _before_ getting the spinlock,
497 * lest we deadlock against the timer routine
498 *
499 * the timer routine will leave DELAYED set if it notices the
500 * CANCELLING flag in time
501 */
502 if (test_bit(SLOW_WORK_DELAYED, &work->flags)) {
503 struct delayed_slow_work *dwork =
504 container_of(work, struct delayed_slow_work, work);
505 del_timer_sync(&dwork->timer);
506 }
507
508 spin_lock_irq(&slow_work_queue_lock);
509
510 if (test_bit(SLOW_WORK_DELAYED, &work->flags)) {
511 /* the timer routine aborted or never happened, so we are left
512 * holding the timer's reference on the item and should just
513 * drop the pending flag and wait for any ongoing execution to
514 * finish */
515 struct delayed_slow_work *dwork =
516 container_of(work, struct delayed_slow_work, work);
517
518 BUG_ON(timer_pending(&dwork->timer));
519 BUG_ON(!list_empty(&work->link));
520
521 clear_bit(SLOW_WORK_DELAYED, &work->flags);
522 put = true;
523 clear_bit(SLOW_WORK_PENDING, &work->flags);
524
525 } else if (test_bit(SLOW_WORK_PENDING, &work->flags) &&
526 !list_empty(&work->link)) {
527 /* the link in the pending queue holds a reference on the item
528 * that we will need to release */
529 list_del_init(&work->link);
530 wait = false;
531 put = true;
532 clear_bit(SLOW_WORK_PENDING, &work->flags);
533
534 } else if (test_and_clear_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags)) {
535 /* the executor is holding our only reference on the item, so
536 * we merely need to wait for it to finish executing */
537 clear_bit(SLOW_WORK_PENDING, &work->flags);
538 }
539
540 spin_unlock_irq(&slow_work_queue_lock);
541
542 /* the EXECUTING flag is set by the executor whilst the spinlock is set
543 * and before the item is dequeued - so assuming the above doesn't
544 * actually dequeue it, simply waiting for the EXECUTING flag to be
545 * released here should be sufficient */
546 if (wait)
547 wait_on_bit(&work->flags, SLOW_WORK_EXECUTING, slow_work_wait,
548 TASK_UNINTERRUPTIBLE);
549
550 clear_bit(SLOW_WORK_CANCELLING, &work->flags);
551 if (put)
552 slow_work_put_ref(work);
553}
554EXPORT_SYMBOL(slow_work_cancel);
555
556/*
557 * Handle expiry of the delay timer, indicating that a delayed slow work item
558 * should now be queued if not cancelled
559 */
560static void delayed_slow_work_timer(unsigned long data)
561{
562 wait_queue_head_t *wfo_wq;
563 struct list_head *queue;
564 struct slow_work *work = (struct slow_work *) data;
565 unsigned long flags;
566 bool queued = false, put = false, first = false;
567
568 if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {
569 wfo_wq = &vslow_work_queue_waits_for_occupation;
570 queue = &vslow_work_queue;
571 } else {
572 wfo_wq = &slow_work_queue_waits_for_occupation;
573 queue = &slow_work_queue;
574 }
575
576 spin_lock_irqsave(&slow_work_queue_lock, flags);
577 if (likely(!test_bit(SLOW_WORK_CANCELLING, &work->flags))) {
578 clear_bit(SLOW_WORK_DELAYED, &work->flags);
579
580 if (test_bit(SLOW_WORK_EXECUTING, &work->flags)) {
581 /* we discard the reference the timer was holding in
582 * favour of the one the executor holds */
583 set_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags);
584 put = true;
585 } else {
586 slow_work_mark_time(work);
587 list_add_tail(&work->link, queue);
588 queued = true;
589 if (work->link.prev == queue)
590 first = true;
591 }
592 }
593
594 spin_unlock_irqrestore(&slow_work_queue_lock, flags);
595 if (put)
596 slow_work_put_ref(work);
597 if (first)
598 wake_up(wfo_wq);
599 if (queued)
600 wake_up(&slow_work_thread_wq);
601}
602
603/**
604 * delayed_slow_work_enqueue - Schedule a delayed slow work item for processing
605 * @dwork: The delayed work item to queue
606 * @delay: When to start executing the work, in jiffies from now
607 *
608 * This is similar to slow_work_enqueue(), but it adds a delay before the work
609 * is actually queued for processing.
610 *
611 * The item can have delayed processing requested on it whilst it is being
612 * executed. The delay will begin immediately, and if it expires before the
613 * item finishes executing, the item will be placed back on the queue when it
614 * has done executing.
615 */
616int delayed_slow_work_enqueue(struct delayed_slow_work *dwork,
617 unsigned long delay)
618{
619 struct slow_work *work = &dwork->work;
620 unsigned long flags;
621 int ret;
622
623 if (delay == 0)
624 return slow_work_enqueue(&dwork->work);
625
626 BUG_ON(slow_work_user_count <= 0);
627 BUG_ON(!work);
628 BUG_ON(!work->ops);
629
630 if (test_bit(SLOW_WORK_CANCELLING, &work->flags))
631 return -ECANCELED;
632
633 if (!test_and_set_bit_lock(SLOW_WORK_PENDING, &work->flags)) {
634 spin_lock_irqsave(&slow_work_queue_lock, flags);
635
636 if (test_bit(SLOW_WORK_CANCELLING, &work->flags))
637 goto cancelled;
638
639 /* the timer holds a reference whilst it is pending */
640 ret = slow_work_get_ref(work);
641 if (ret < 0)
642 goto cant_get_ref;
643
644 if (test_and_set_bit(SLOW_WORK_DELAYED, &work->flags))
645 BUG();
646 dwork->timer.expires = jiffies + delay;
647 dwork->timer.data = (unsigned long) work;
648 dwork->timer.function = delayed_slow_work_timer;
649 add_timer(&dwork->timer);
650
651 spin_unlock_irqrestore(&slow_work_queue_lock, flags);
652 }
653
654 return 0;
655
656cancelled:
657 ret = -ECANCELED;
658cant_get_ref:
659 spin_unlock_irqrestore(&slow_work_queue_lock, flags);
660 return ret;
661}
662EXPORT_SYMBOL(delayed_slow_work_enqueue);
663
664/*
665 * Schedule a cull of the thread pool at some time in the near future
666 */
667static void slow_work_schedule_cull(void)
668{
669 mod_timer(&slow_work_cull_timer,
670 round_jiffies(jiffies + SLOW_WORK_CULL_TIMEOUT));
671}
672
673/*
674 * Worker thread culling algorithm
675 */
676static bool slow_work_cull_thread(void)
677{
678 unsigned long flags;
679 bool do_cull = false;
680
681 spin_lock_irqsave(&slow_work_queue_lock, flags);
682
683 if (slow_work_cull) {
684 slow_work_cull = false;
685
686 if (list_empty(&slow_work_queue) &&
687 list_empty(&vslow_work_queue) &&
688 atomic_read(&slow_work_thread_count) >
689 slow_work_min_threads) {
690 slow_work_schedule_cull();
691 do_cull = true;
692 }
693 }
694
695 spin_unlock_irqrestore(&slow_work_queue_lock, flags);
696 return do_cull;
697}
698
699/*
700 * Determine if there is slow work available for dispatch
701 */
702static inline bool slow_work_available(int vsmax)
703{
704 return !list_empty(&slow_work_queue) ||
705 (!list_empty(&vslow_work_queue) &&
706 atomic_read(&vslow_work_executing_count) < vsmax);
707}
708
709/*
710 * Worker thread dispatcher
711 */
712static int slow_work_thread(void *_data)
713{
714 int vsmax, id;
715
716 DEFINE_WAIT(wait);
717
718 set_freezable();
719 set_user_nice(current, -5);
720
721 /* allocate ourselves an ID */
722 spin_lock_irq(&slow_work_queue_lock);
723 id = find_first_zero_bit(slow_work_ids, SLOW_WORK_THREAD_LIMIT);
724 BUG_ON(id < 0 || id >= SLOW_WORK_THREAD_LIMIT);
725 __set_bit(id, slow_work_ids);
726 slow_work_set_thread_pid(id, current->pid);
727 spin_unlock_irq(&slow_work_queue_lock);
728
729 sprintf(current->comm, "kslowd%03u", id);
730
731 for (;;) {
732 vsmax = vslow_work_proportion;
733 vsmax *= atomic_read(&slow_work_thread_count);
734 vsmax /= 100;
735
736 prepare_to_wait_exclusive(&slow_work_thread_wq, &wait,
737 TASK_INTERRUPTIBLE);
738 if (!freezing(current) &&
739 !slow_work_threads_should_exit &&
740 !slow_work_available(vsmax) &&
741 !slow_work_cull)
742 schedule();
743 finish_wait(&slow_work_thread_wq, &wait);
744
745 try_to_freeze();
746
747 vsmax = vslow_work_proportion;
748 vsmax *= atomic_read(&slow_work_thread_count);
749 vsmax /= 100;
750
751 if (slow_work_available(vsmax) && slow_work_execute(id)) {
752 cond_resched();
753 if (list_empty(&slow_work_queue) &&
754 list_empty(&vslow_work_queue) &&
755 atomic_read(&slow_work_thread_count) >
756 slow_work_min_threads)
757 slow_work_schedule_cull();
758 continue;
759 }
760
761 if (slow_work_threads_should_exit)
762 break;
763
764 if (slow_work_cull && slow_work_cull_thread())
765 break;
766 }
767
768 spin_lock_irq(&slow_work_queue_lock);
769 slow_work_set_thread_pid(id, 0);
770 __clear_bit(id, slow_work_ids);
771 spin_unlock_irq(&slow_work_queue_lock);
772
773 if (atomic_dec_and_test(&slow_work_thread_count))
774 complete_and_exit(&slow_work_last_thread_exited, 0);
775 return 0;
776}
777
778/*
779 * Handle thread cull timer expiration
780 */
781static void slow_work_cull_timeout(unsigned long data)
782{
783 slow_work_cull = true;
784 wake_up(&slow_work_thread_wq);
785}
786
787/*
788 * Start a new slow work thread
789 */
790static void slow_work_new_thread_execute(struct slow_work *work)
791{
792 struct task_struct *p;
793
794 if (slow_work_threads_should_exit)
795 return;
796
797 if (atomic_read(&slow_work_thread_count) >= slow_work_max_threads)
798 return;
799
800 if (!mutex_trylock(&slow_work_user_lock))
801 return;
802
803 slow_work_may_not_start_new_thread = true;
804 atomic_inc(&slow_work_thread_count);
805 p = kthread_run(slow_work_thread, NULL, "kslowd");
806 if (IS_ERR(p)) {
807 printk(KERN_DEBUG "Slow work thread pool: OOM\n");
808 if (atomic_dec_and_test(&slow_work_thread_count))
809 BUG(); /* we're running on a slow work thread... */
810 mod_timer(&slow_work_oom_timer,
811 round_jiffies(jiffies + SLOW_WORK_OOM_TIMEOUT));
812 } else {
813 /* ratelimit the starting of new threads */
814 mod_timer(&slow_work_oom_timer, jiffies + 1);
815 }
816
817 mutex_unlock(&slow_work_user_lock);
818}
819
820static const struct slow_work_ops slow_work_new_thread_ops = {
821 .owner = THIS_MODULE,
822 .execute = slow_work_new_thread_execute,
823#ifdef CONFIG_SLOW_WORK_DEBUG
824 .desc = slow_work_new_thread_desc,
825#endif
826};
827
828/*
829 * post-OOM new thread start suppression expiration
830 */
831static void slow_work_oom_timeout(unsigned long data)
832{
833 slow_work_may_not_start_new_thread = false;
834}
835
836#ifdef CONFIG_SYSCTL
837/*
838 * Handle adjustment of the minimum number of threads
839 */
840static int slow_work_min_threads_sysctl(struct ctl_table *table, int write,
841 void __user *buffer,
842 size_t *lenp, loff_t *ppos)
843{
844 int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
845 int n;
846
847 if (ret == 0) {
848 mutex_lock(&slow_work_user_lock);
849 if (slow_work_user_count > 0) {
850 /* see if we need to start or stop threads */
851 n = atomic_read(&slow_work_thread_count) -
852 slow_work_min_threads;
853
854 if (n < 0 && !slow_work_may_not_start_new_thread)
855 slow_work_enqueue(&slow_work_new_thread);
856 else if (n > 0)
857 slow_work_schedule_cull();
858 }
859 mutex_unlock(&slow_work_user_lock);
860 }
861
862 return ret;
863}
864
865/*
866 * Handle adjustment of the maximum number of threads
867 */
868static int slow_work_max_threads_sysctl(struct ctl_table *table, int write,
869 void __user *buffer,
870 size_t *lenp, loff_t *ppos)
871{
872 int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
873 int n;
874
875 if (ret == 0) {
876 mutex_lock(&slow_work_user_lock);
877 if (slow_work_user_count > 0) {
878 /* see if we need to stop threads */
879 n = slow_work_max_threads -
880 atomic_read(&slow_work_thread_count);
881
882 if (n < 0)
883 slow_work_schedule_cull();
884 }
885 mutex_unlock(&slow_work_user_lock);
886 }
887
888 return ret;
889}
890#endif /* CONFIG_SYSCTL */
891
892/**
893 * slow_work_register_user - Register a user of the facility
894 * @module: The module about to make use of the facility
895 *
896 * Register a user of the facility, starting up the initial threads if there
897 * aren't any other users at this point. This will return 0 if successful, or
898 * an error if not.
899 */
900int slow_work_register_user(struct module *module)
901{
902 struct task_struct *p;
903 int loop;
904
905 mutex_lock(&slow_work_user_lock);
906
907 if (slow_work_user_count == 0) {
908 printk(KERN_NOTICE "Slow work thread pool: Starting up\n");
909 init_completion(&slow_work_last_thread_exited);
910
911 slow_work_threads_should_exit = false;
912 slow_work_init(&slow_work_new_thread,
913 &slow_work_new_thread_ops);
914 slow_work_may_not_start_new_thread = false;
915 slow_work_cull = false;
916
917 /* start the minimum number of threads */
918 for (loop = 0; loop < slow_work_min_threads; loop++) {
919 atomic_inc(&slow_work_thread_count);
920 p = kthread_run(slow_work_thread, NULL, "kslowd");
921 if (IS_ERR(p))
922 goto error;
923 }
924 printk(KERN_NOTICE "Slow work thread pool: Ready\n");
925 }
926
927 slow_work_user_count++;
928 mutex_unlock(&slow_work_user_lock);
929 return 0;
930
931error:
932 if (atomic_dec_and_test(&slow_work_thread_count))
933 complete(&slow_work_last_thread_exited);
934 if (loop > 0) {
935 printk(KERN_ERR "Slow work thread pool:"
936 " Aborting startup on ENOMEM\n");
937 slow_work_threads_should_exit = true;
938 wake_up_all(&slow_work_thread_wq);
939 wait_for_completion(&slow_work_last_thread_exited);
940 printk(KERN_ERR "Slow work thread pool: Aborted\n");
941 }
942 mutex_unlock(&slow_work_user_lock);
943 return PTR_ERR(p);
944}
945EXPORT_SYMBOL(slow_work_register_user);
946
947/*
948 * wait for all outstanding items from the calling module to complete
949 * - note that more items may be queued whilst we're waiting
950 */
951static void slow_work_wait_for_items(struct module *module)
952{
953#ifdef CONFIG_MODULES
954 DECLARE_WAITQUEUE(myself, current);
955 struct slow_work *work;
956 int loop;
957
958 mutex_lock(&slow_work_unreg_sync_lock);
959 add_wait_queue(&slow_work_unreg_wq, &myself);
960
961 for (;;) {
962 spin_lock_irq(&slow_work_queue_lock);
963
964 /* first of all, we wait for the last queued item in each list
965 * to be processed */
966 list_for_each_entry_reverse(work, &vslow_work_queue, link) {
967 if (work->owner == module) {
968 set_current_state(TASK_UNINTERRUPTIBLE);
969 slow_work_unreg_work_item = work;
970 goto do_wait;
971 }
972 }
973 list_for_each_entry_reverse(work, &slow_work_queue, link) {
974 if (work->owner == module) {
975 set_current_state(TASK_UNINTERRUPTIBLE);
976 slow_work_unreg_work_item = work;
977 goto do_wait;
978 }
979 }
980
981 /* then we wait for the items being processed to finish */
982 slow_work_unreg_module = module;
983 smp_mb();
984 for (loop = 0; loop < SLOW_WORK_THREAD_LIMIT; loop++) {
985 if (slow_work_thread_processing[loop] == module)
986 goto do_wait;
987 }
988 spin_unlock_irq(&slow_work_queue_lock);
989 break; /* okay, we're done */
990
991 do_wait:
992 spin_unlock_irq(&slow_work_queue_lock);
993 schedule();
994 slow_work_unreg_work_item = NULL;
995 slow_work_unreg_module = NULL;
996 }
997
998 remove_wait_queue(&slow_work_unreg_wq, &myself);
999 mutex_unlock(&slow_work_unreg_sync_lock);
1000#endif /* CONFIG_MODULES */
1001}
1002
1003/**
1004 * slow_work_unregister_user - Unregister a user of the facility
1005 * @module: The module whose items should be cleared
1006 *
1007 * Unregister a user of the facility, killing all the threads if this was the
1008 * last one.
1009 *
1010 * This waits for all the work items belonging to the nominated module to go
1011 * away before proceeding.
1012 */
1013void slow_work_unregister_user(struct module *module)
1014{
1015 /* first of all, wait for all outstanding items from the calling module
1016 * to complete */
1017 if (module)
1018 slow_work_wait_for_items(module);
1019
1020 /* then we can actually go about shutting down the facility if need
1021 * be */
1022 mutex_lock(&slow_work_user_lock);
1023
1024 BUG_ON(slow_work_user_count <= 0);
1025
1026 slow_work_user_count--;
1027 if (slow_work_user_count == 0) {
1028 printk(KERN_NOTICE "Slow work thread pool: Shutting down\n");
1029 slow_work_threads_should_exit = true;
1030 del_timer_sync(&slow_work_cull_timer);
1031 del_timer_sync(&slow_work_oom_timer);
1032 wake_up_all(&slow_work_thread_wq);
1033 wait_for_completion(&slow_work_last_thread_exited);
1034 printk(KERN_NOTICE "Slow work thread pool:"
1035 " Shut down complete\n");
1036 }
1037
1038 mutex_unlock(&slow_work_user_lock);
1039}
1040EXPORT_SYMBOL(slow_work_unregister_user);
1041
1042/*
1043 * Initialise the slow work facility
1044 */
1045static int __init init_slow_work(void)
1046{
1047 unsigned nr_cpus = num_possible_cpus();
1048
1049 if (slow_work_max_threads < nr_cpus)
1050 slow_work_max_threads = nr_cpus;
1051#ifdef CONFIG_SYSCTL
1052 if (slow_work_max_max_threads < nr_cpus * 2)
1053 slow_work_max_max_threads = nr_cpus * 2;
1054#endif
1055#ifdef CONFIG_SLOW_WORK_DEBUG
1056 {
1057 struct dentry *dbdir;
1058
1059 dbdir = debugfs_create_dir("slow_work", NULL);
1060 if (dbdir && !IS_ERR(dbdir))
1061 debugfs_create_file("runqueue", S_IFREG | 0400, dbdir,
1062 NULL, &slow_work_runqueue_fops);
1063 }
1064#endif
1065 return 0;
1066}
1067
1068subsys_initcall(init_slow_work);
generated by cgit v1.2.2 (git 2.25.0) at 2025-10-31 23:56:15 -0400