kernel/slow-work.c

   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
  22 static void slow_work_cull_timeout(unsigned long);
  23 static void slow_work_oom_timeout(unsigned long);
  24
  25 #ifdef CONFIG_SYSCTL
  26 static int slow_work_min_threads_sysctl(struct ctl_table *, int,
  27                                         void __user *, size_t *, loff_t *);
  28
  29 static 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  */
  39 static unsigned slow_work_min_threads = 2;
  40 static unsigned slow_work_max_threads = 4;
  41 static unsigned vslow_work_proportion = 50; /* % of threads that may process
  42                                              * very slow work */
  43
  44 #ifdef CONFIG_SYSCTL
  45 static const int slow_work_min_min_threads = 2;
  46 static int slow_work_max_max_threads = SLOW_WORK_THREAD_LIMIT;
  47 static const int slow_work_min_vslow = 1;
  48 static const int slow_work_max_vslow = 99;
  49
  50 ctl_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  */
  85 static atomic_t slow_work_thread_count;
  86 static atomic_t vslow_work_executing_count;
  87
  88 static bool slow_work_may_not_start_new_thread;
  89 static bool slow_work_cull; /* cull a thread due to lack of activity */
  90 static DEFINE_TIMER(slow_work_cull_timer, slow_work_cull_timeout, 0, 0);
  91 static DEFINE_TIMER(slow_work_oom_timer, slow_work_oom_timeout, 0, 0);
  92 static struct slow_work slow_work_new_thread; /* new thread starter */
  93
  94 /*
  95  * slow work ID allocation (use slow_work_queue_lock)
  96  */
  97 static 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
 104 static struct module *slow_work_thread_processing[SLOW_WORK_THREAD_LIMIT];
 105 static struct module *slow_work_unreg_module;
 106 static struct slow_work *slow_work_unreg_work_item;
 107 static DECLARE_WAIT_QUEUE_HEAD(slow_work_unreg_wq);
 108 static DEFINE_MUTEX(slow_work_unreg_sync_lock);
 109
 110 static 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 }
 115 static 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 }
 125 static void slow_work_clear_thread_processing(int id)
 126 {
 127         slow_work_thread_processing[id] = NULL;
 128 }
 129 #else
 130 static void slow_work_set_thread_processing(int id, struct slow_work *work) {}
 131 static void slow_work_done_thread_processing(int id, struct slow_work *work) {}
 132 static 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
 139 struct slow_work *slow_work_execs[SLOW_WORK_THREAD_LIMIT];
 140 pid_t slow_work_pids[SLOW_WORK_THREAD_LIMIT];
 141 DEFINE_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  */
 152 LIST_HEAD(slow_work_queue);
 153 LIST_HEAD(vslow_work_queue);
 154 DEFINE_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  */
 162 static DECLARE_WAIT_QUEUE_HEAD(slow_work_queue_waits_for_occupation);
 163 static 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  */
 170 static bool slow_work_threads_should_exit;
 171 static DECLARE_WAIT_QUEUE_HEAD(slow_work_thread_wq);
 172 static 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  */
 179 static int slow_work_user_count;
 180 static DEFINE_MUTEX(slow_work_user_lock);
 181
 182 static 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
 190 static 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  */
 205 static 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  */
 219 static 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
 309 auto_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  */
 340 bool 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 }
 366 EXPORT_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  */
 396 int 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
 466 cancelled:
 467         ret = -ECANCELED;
 468 failed:
 469         spin_unlock_irqrestore(&slow_work_queue_lock, flags);
 470         return ret;
 471 }
 472 EXPORT_SYMBOL(slow_work_enqueue);
 473
 474 static 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  */
 488 void 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 }
 554 EXPORT_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  */
 560 static 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  */
 616 int 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
 656 cancelled:
 657         ret = -ECANCELED;
 658 cant_get_ref:
 659         spin_unlock_irqrestore(&slow_work_queue_lock, flags);
 660         return ret;
 661 }
 662 EXPORT_SYMBOL(delayed_slow_work_enqueue);
 663
 664 /*
 665  * Schedule a cull of the thread pool at some time in the near future
 666  */
 667 static 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  */
 676 static 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  */
 702 static 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  */
 712 static 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  */
 781 static 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  */
 790 static 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
 820 static 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  */
 831 static 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  */
 840 static 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  */
 868 static 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  */
 900 int 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
 931 error:
 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 }
 945 EXPORT_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  */
 951 static 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  */
1013 void 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 }
1040 EXPORT_SYMBOL(slow_work_unregister_user);
1041
1042 /*
1043  * Initialise the slow work facility
1044  */
1045 static 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
1068 subsys_initcall(init_slow_work);