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                 .ctl_name       = CTL_UNNUMBERED,
  53                 .procname       = "min-threads",
  54                 .data           = &slow_work_min_threads,
  55                 .maxlen         = sizeof(unsigned),
  56                 .mode           = 0644,
  57                 .proc_handler   = slow_work_min_threads_sysctl,
  58                 .extra1         = (void *) &slow_work_min_min_threads,
  59                 .extra2         = &slow_work_max_threads,
  60         },
  61         {
  62                 .ctl_name       = CTL_UNNUMBERED,
  63                 .procname       = "max-threads",
  64                 .data           = &slow_work_max_threads,
  65                 .maxlen         = sizeof(unsigned),
  66                 .mode           = 0644,
  67                 .proc_handler   = slow_work_max_threads_sysctl,
  68                 .extra1         = &slow_work_min_threads,
  69                 .extra2         = (void *) &slow_work_max_max_threads,
  70         },
  71         {
  72                 .ctl_name       = CTL_UNNUMBERED,
  73                 .procname       = "vslow-percentage",
  74                 .data           = &vslow_work_proportion,
  75                 .maxlen         = sizeof(unsigned),
  76                 .mode           = 0644,
  77                 .proc_handler   = &proc_dointvec_minmax,
  78                 .extra1         = (void *) &slow_work_min_vslow,
  79                 .extra2         = (void *) &slow_work_max_vslow,
  80         },
  81         { .ctl_name = 0 }
  82 };
  83 #endif
  84
  85 /*
  86  * The active state of the thread pool
  87  */
  88 static atomic_t slow_work_thread_count;
  89 static atomic_t vslow_work_executing_count;
  90
  91 static bool slow_work_may_not_start_new_thread;
  92 static bool slow_work_cull; /* cull a thread due to lack of activity */
  93 static DEFINE_TIMER(slow_work_cull_timer, slow_work_cull_timeout, 0, 0);
  94 static DEFINE_TIMER(slow_work_oom_timer, slow_work_oom_timeout, 0, 0);
  95 static struct slow_work slow_work_new_thread; /* new thread starter */
  96
  97 /*
  98  * slow work ID allocation (use slow_work_queue_lock)
  99  */
 100 static DECLARE_BITMAP(slow_work_ids, SLOW_WORK_THREAD_LIMIT);
 101
 102 /*
 103  * Unregistration tracking to prevent put_ref() from disappearing during module
 104  * unload
 105  */
 106 #ifdef CONFIG_MODULES
 107 static struct module *slow_work_thread_processing[SLOW_WORK_THREAD_LIMIT];
 108 static struct module *slow_work_unreg_module;
 109 static struct slow_work *slow_work_unreg_work_item;
 110 static DECLARE_WAIT_QUEUE_HEAD(slow_work_unreg_wq);
 111 static DEFINE_MUTEX(slow_work_unreg_sync_lock);
 112
 113 static void slow_work_set_thread_processing(int id, struct slow_work *work)
 114 {
 115         if (work)
 116                 slow_work_thread_processing[id] = work->owner;
 117 }
 118 static void slow_work_done_thread_processing(int id, struct slow_work *work)
 119 {
 120         struct module *module = slow_work_thread_processing[id];
 121
 122         slow_work_thread_processing[id] = NULL;
 123         smp_mb();
 124         if (slow_work_unreg_work_item == work ||
 125             slow_work_unreg_module == module)
 126                 wake_up_all(&slow_work_unreg_wq);
 127 }
 128 static void slow_work_clear_thread_processing(int id)
 129 {
 130         slow_work_thread_processing[id] = NULL;
 131 }
 132 #else
 133 static void slow_work_set_thread_processing(int id, struct slow_work *work) {}
 134 static void slow_work_done_thread_processing(int id, struct slow_work *work) {}
 135 static void slow_work_clear_thread_processing(int id) {}
 136 #endif
 137
 138 /*
 139  * Data for tracking currently executing items for indication through /proc
 140  */
 141 #ifdef CONFIG_SLOW_WORK_DEBUG
 142 struct slow_work *slow_work_execs[SLOW_WORK_THREAD_LIMIT];
 143 pid_t slow_work_pids[SLOW_WORK_THREAD_LIMIT];
 144 DEFINE_RWLOCK(slow_work_execs_lock);
 145 #endif
 146
 147 /*
 148  * The queues of work items and the lock governing access to them.  These are
 149  * shared between all the CPUs.  It doesn't make sense to have per-CPU queues
 150  * as the number of threads bears no relation to the number of CPUs.
 151  *
 152  * There are two queues of work items: one for slow work items, and one for
 153  * very slow work items.
 154  */
 155 LIST_HEAD(slow_work_queue);
 156 LIST_HEAD(vslow_work_queue);
 157 DEFINE_SPINLOCK(slow_work_queue_lock);
 158
 159 /*
 160  * The following are two wait queues that get pinged when a work item is placed
 161  * on an empty queue.  These allow work items that are hogging a thread by
 162  * sleeping in a way that could be deferred to yield their thread and enqueue
 163  * themselves.
 164  */
 165 static DECLARE_WAIT_QUEUE_HEAD(slow_work_queue_waits_for_occupation);
 166 static DECLARE_WAIT_QUEUE_HEAD(vslow_work_queue_waits_for_occupation);
 167
 168 /*
 169  * The thread controls.  A variable used to signal to the threads that they
 170  * should exit when the queue is empty, a waitqueue used by the threads to wait
 171  * for signals, and a completion set by the last thread to exit.
 172  */
 173 static bool slow_work_threads_should_exit;
 174 static DECLARE_WAIT_QUEUE_HEAD(slow_work_thread_wq);
 175 static DECLARE_COMPLETION(slow_work_last_thread_exited);
 176
 177 /*
 178  * The number of users of the thread pool and its lock.  Whilst this is zero we
 179  * have no threads hanging around, and when this reaches zero, we wait for all
 180  * active or queued work items to complete and kill all the threads we do have.
 181  */
 182 static int slow_work_user_count;
 183 static DEFINE_MUTEX(slow_work_user_lock);
 184
 185 static inline int slow_work_get_ref(struct slow_work *work)
 186 {
 187         if (work->ops->get_ref)
 188                 return work->ops->get_ref(work);
 189
 190         return 0;
 191 }
 192
 193 static inline void slow_work_put_ref(struct slow_work *work)
 194 {
 195         if (work->ops->put_ref)
 196                 work->ops->put_ref(work);
 197 }
 198
 199 /*
 200  * Calculate the maximum number of active threads in the pool that are
 201  * permitted to process very slow work items.
 202  *
 203  * The answer is rounded up to at least 1, but may not equal or exceed the
 204  * maximum number of the threads in the pool.  This means we always have at
 205  * least one thread that can process slow work items, and we always have at
 206  * least one thread that won't get tied up doing so.
 207  */
 208 static unsigned slow_work_calc_vsmax(void)
 209 {
 210         unsigned vsmax;
 211
 212         vsmax = atomic_read(&slow_work_thread_count) * vslow_work_proportion;
 213         vsmax /= 100;
 214         vsmax = max(vsmax, 1U);
 215         return min(vsmax, slow_work_max_threads - 1);
 216 }
 217
 218 /*
 219  * Attempt to execute stuff queued on a slow thread.  Return true if we managed
 220  * it, false if there was nothing to do.
 221  */
 222 static noinline bool slow_work_execute(int id)
 223 {
 224         struct slow_work *work = NULL;
 225         unsigned vsmax;
 226         bool very_slow;
 227
 228         vsmax = slow_work_calc_vsmax();
 229
 230         /* see if we can schedule a new thread to be started if we're not
 231          * keeping up with the work */
 232         if (!waitqueue_active(&slow_work_thread_wq) &&
 233             (!list_empty(&slow_work_queue) || !list_empty(&vslow_work_queue)) &&
 234             atomic_read(&slow_work_thread_count) < slow_work_max_threads &&
 235             !slow_work_may_not_start_new_thread)
 236                 slow_work_enqueue(&slow_work_new_thread);
 237
 238         /* find something to execute */
 239         spin_lock_irq(&slow_work_queue_lock);
 240         if (!list_empty(&vslow_work_queue) &&
 241             atomic_read(&vslow_work_executing_count) < vsmax) {
 242                 work = list_entry(vslow_work_queue.next,
 243                                   struct slow_work, link);
 244                 if (test_and_set_bit_lock(SLOW_WORK_EXECUTING, &work->flags))
 245                         BUG();
 246                 list_del_init(&work->link);
 247                 atomic_inc(&vslow_work_executing_count);
 248                 very_slow = true;
 249         } else if (!list_empty(&slow_work_queue)) {
 250                 work = list_entry(slow_work_queue.next,
 251                                   struct slow_work, link);
 252                 if (test_and_set_bit_lock(SLOW_WORK_EXECUTING, &work->flags))
 253                         BUG();
 254                 list_del_init(&work->link);
 255                 very_slow = false;
 256         } else {
 257                 very_slow = false; /* avoid the compiler warning */
 258         }
 259
 260         slow_work_set_thread_processing(id, work);
 261         if (work) {
 262                 slow_work_mark_time(work);
 263                 slow_work_begin_exec(id, work);
 264         }
 265
 266         spin_unlock_irq(&slow_work_queue_lock);
 267
 268         if (!work)
 269                 return false;
 270
 271         if (!test_and_clear_bit(SLOW_WORK_PENDING, &work->flags))
 272                 BUG();
 273
 274         /* don't execute if the work is in the process of being cancelled */
 275         if (!test_bit(SLOW_WORK_CANCELLING, &work->flags))
 276                 work->ops->execute(work);
 277
 278         if (very_slow)
 279                 atomic_dec(&vslow_work_executing_count);
 280         clear_bit_unlock(SLOW_WORK_EXECUTING, &work->flags);
 281
 282         /* wake up anyone waiting for this work to be complete */
 283         wake_up_bit(&work->flags, SLOW_WORK_EXECUTING);
 284
 285         slow_work_end_exec(id, work);
 286
 287         /* if someone tried to enqueue the item whilst we were executing it,
 288          * then it'll be left unenqueued to avoid multiple threads trying to
 289          * execute it simultaneously
 290          *
 291          * there is, however, a race between us testing the pending flag and
 292          * getting the spinlock, and between the enqueuer setting the pending
 293          * flag and getting the spinlock, so we use a deferral bit to tell us
 294          * if the enqueuer got there first
 295          */
 296         if (test_bit(SLOW_WORK_PENDING, &work->flags)) {
 297                 spin_lock_irq(&slow_work_queue_lock);
 298
 299                 if (!test_bit(SLOW_WORK_EXECUTING, &work->flags) &&
 300                     test_and_clear_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags))
 301                         goto auto_requeue;
 302
 303                 spin_unlock_irq(&slow_work_queue_lock);
 304         }
 305
 306         /* sort out the race between module unloading and put_ref() */
 307         slow_work_put_ref(work);
 308         slow_work_done_thread_processing(id, work);
 309
 310         return true;
 311
 312 auto_requeue:
 313         /* we must complete the enqueue operation
 314          * - we transfer our ref on the item back to the appropriate queue
 315          * - don't wake another thread up as we're awake already
 316          */
 317         slow_work_mark_time(work);
 318         if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags))
 319                 list_add_tail(&work->link, &vslow_work_queue);
 320         else
 321                 list_add_tail(&work->link, &slow_work_queue);
 322         spin_unlock_irq(&slow_work_queue_lock);
 323         slow_work_clear_thread_processing(id);
 324         return true;
 325 }
 326
 327 /**
 328  * slow_work_sleep_till_thread_needed - Sleep till thread needed by other work
 329  * work: The work item under execution that wants to sleep
 330  * _timeout: Scheduler sleep timeout
 331  *
 332  * Allow a requeueable work item to sleep on a slow-work processor thread until
 333  * that thread is needed to do some other work or the sleep is interrupted by
 334  * some other event.
 335  *
 336  * The caller must set up a wake up event before calling this and must have set
 337  * the appropriate sleep mode (such as TASK_UNINTERRUPTIBLE) and tested its own
 338  * condition before calling this function as no test is made here.
 339  *
 340  * False is returned if there is nothing on the queue; true is returned if the
 341  * work item should be requeued
 342  */
 343 bool slow_work_sleep_till_thread_needed(struct slow_work *work,
 344                                         signed long *_timeout)
 345 {
 346         wait_queue_head_t *wfo_wq;
 347         struct list_head *queue;
 348
 349         DEFINE_WAIT(wait);
 350
 351         if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {
 352                 wfo_wq = &vslow_work_queue_waits_for_occupation;
 353                 queue = &vslow_work_queue;
 354         } else {
 355                 wfo_wq = &slow_work_queue_waits_for_occupation;
 356                 queue = &slow_work_queue;
 357         }
 358
 359         if (!list_empty(queue))
 360                 return true;
 361
 362         add_wait_queue_exclusive(wfo_wq, &wait);
 363         if (list_empty(queue))
 364                 *_timeout = schedule_timeout(*_timeout);
 365         finish_wait(wfo_wq, &wait);
 366
 367         return !list_empty(queue);
 368 }
 369 EXPORT_SYMBOL(slow_work_sleep_till_thread_needed);
 370
 371 /**
 372  * slow_work_enqueue - Schedule a slow work item for processing
 373  * @work: The work item to queue
 374  *
 375  * Schedule a slow work item for processing.  If the item is already undergoing
 376  * execution, this guarantees not to re-enter the execution routine until the
 377  * first execution finishes.
 378  *
 379  * The item is pinned by this function as it retains a reference to it, managed
 380  * through the item operations.  The item is unpinned once it has been
 381  * executed.
 382  *
 383  * An item may hog the thread that is running it for a relatively large amount
 384  * of time, sufficient, for example, to perform several lookup, mkdir, create
 385  * and setxattr operations.  It may sleep on I/O and may sleep to obtain locks.
 386  *
 387  * Conversely, if a number of items are awaiting processing, it may take some
 388  * time before any given item is given attention.  The number of threads in the
 389  * pool may be increased to deal with demand, but only up to a limit.
 390  *
 391  * If SLOW_WORK_VERY_SLOW is set on the work item, then it will be placed in
 392  * the very slow queue, from which only a portion of the threads will be
 393  * allowed to pick items to execute.  This ensures that very slow items won't
 394  * overly block ones that are just ordinarily slow.
 395  *
 396  * Returns 0 if successful, -EAGAIN if not (or -ECANCELED if cancelled work is
 397  * attempted queued)
 398  */
 399 int slow_work_enqueue(struct slow_work *work)
 400 {
 401         wait_queue_head_t *wfo_wq;
 402         struct list_head *queue;
 403         unsigned long flags;
 404         int ret;
 405
 406         if (test_bit(SLOW_WORK_CANCELLING, &work->flags))
 407                 return -ECANCELED;
 408
 409         BUG_ON(slow_work_user_count <= 0);
 410         BUG_ON(!work);
 411         BUG_ON(!work->ops);
 412
 413         /* when honouring an enqueue request, we only promise that we will run
 414          * the work function in the future; we do not promise to run it once
 415          * per enqueue request
 416          *
 417          * we use the PENDING bit to merge together repeat requests without
 418          * having to disable IRQs and take the spinlock, whilst still
 419          * maintaining our promise
 420          */
 421         if (!test_and_set_bit_lock(SLOW_WORK_PENDING, &work->flags)) {
 422                 if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {
 423                         wfo_wq = &vslow_work_queue_waits_for_occupation;
 424                         queue = &vslow_work_queue;
 425                 } else {
 426                         wfo_wq = &slow_work_queue_waits_for_occupation;
 427                         queue = &slow_work_queue;
 428                 }
 429
 430                 spin_lock_irqsave(&slow_work_queue_lock, flags);
 431
 432                 if (unlikely(test_bit(SLOW_WORK_CANCELLING, &work->flags)))
 433                         goto cancelled;
 434
 435                 /* we promise that we will not attempt to execute the work
 436                  * function in more than one thread simultaneously
 437                  *
 438                  * this, however, leaves us with a problem if we're asked to
 439                  * enqueue the work whilst someone is executing the work
 440                  * function as simply queueing the work immediately means that
 441                  * another thread may try executing it whilst it is already
 442                  * under execution
 443                  *
 444                  * to deal with this, we set the ENQ_DEFERRED bit instead of
 445                  * enqueueing, and the thread currently executing the work
 446                  * function will enqueue the work item when the work function
 447                  * returns and it has cleared the EXECUTING bit
 448                  */
 449                 if (test_bit(SLOW_WORK_EXECUTING, &work->flags)) {
 450                         set_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags);
 451                 } else {
 452                         ret = slow_work_get_ref(work);
 453                         if (ret < 0)
 454                                 goto failed;
 455                         slow_work_mark_time(work);
 456                         list_add_tail(&work->link, queue);
 457                         wake_up(&slow_work_thread_wq);
 458
 459                         /* if someone who could be requeued is sleeping on a
 460                          * thread, then ask them to yield their thread */
 461                         if (work->link.prev == queue)
 462                                 wake_up(wfo_wq);
 463                 }
 464
 465                 spin_unlock_irqrestore(&slow_work_queue_lock, flags);
 466         }
 467         return 0;
 468
 469 cancelled:
 470         ret = -ECANCELED;
 471 failed:
 472         spin_unlock_irqrestore(&slow_work_queue_lock, flags);
 473         return ret;
 474 }
 475 EXPORT_SYMBOL(slow_work_enqueue);
 476
 477 static int slow_work_wait(void *word)
 478 {
 479         schedule();
 480         return 0;
 481 }
 482
 483 /**
 484  * slow_work_cancel - Cancel a slow work item
 485  * @work: The work item to cancel
 486  *
 487  * This function will cancel a previously enqueued work item. If we cannot
 488  * cancel the work item, it is guarenteed to have run when this function
 489  * returns.
 490  */
 491 void slow_work_cancel(struct slow_work *work)
 492 {
 493         bool wait = true, put = false;
 494
 495         set_bit(SLOW_WORK_CANCELLING, &work->flags);
 496         smp_mb();
 497
 498         /* if the work item is a delayed work item with an active timer, we
 499          * need to wait for the timer to finish _before_ getting the spinlock,
 500          * lest we deadlock against the timer routine
 501          *
 502          * the timer routine will leave DELAYED set if it notices the
 503          * CANCELLING flag in time
 504          */
 505         if (test_bit(SLOW_WORK_DELAYED, &work->flags)) {
 506                 struct delayed_slow_work *dwork =
 507                         container_of(work, struct delayed_slow_work, work);
 508                 del_timer_sync(&dwork->timer);
 509         }
 510
 511         spin_lock_irq(&slow_work_queue_lock);
 512
 513         if (test_bit(SLOW_WORK_DELAYED, &work->flags)) {
 514                 /* the timer routine aborted or never happened, so we are left
 515                  * holding the timer's reference on the item and should just
 516                  * drop the pending flag and wait for any ongoing execution to
 517                  * finish */
 518                 struct delayed_slow_work *dwork =
 519                         container_of(work, struct delayed_slow_work, work);
 520
 521                 BUG_ON(timer_pending(&dwork->timer));
 522                 BUG_ON(!list_empty(&work->link));
 523
 524                 clear_bit(SLOW_WORK_DELAYED, &work->flags);
 525                 put = true;
 526                 clear_bit(SLOW_WORK_PENDING, &work->flags);
 527
 528         } else if (test_bit(SLOW_WORK_PENDING, &work->flags) &&
 529                    !list_empty(&work->link)) {
 530                 /* the link in the pending queue holds a reference on the item
 531                  * that we will need to release */
 532                 list_del_init(&work->link);
 533                 wait = false;
 534                 put = true;
 535                 clear_bit(SLOW_WORK_PENDING, &work->flags);
 536
 537         } else if (test_and_clear_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags)) {
 538                 /* the executor is holding our only reference on the item, so
 539                  * we merely need to wait for it to finish executing */
 540                 clear_bit(SLOW_WORK_PENDING, &work->flags);
 541         }
 542
 543         spin_unlock_irq(&slow_work_queue_lock);
 544
 545         /* the EXECUTING flag is set by the executor whilst the spinlock is set
 546          * and before the item is dequeued - so assuming the above doesn't
 547          * actually dequeue it, simply waiting for the EXECUTING flag to be
 548          * released here should be sufficient */
 549         if (wait)
 550                 wait_on_bit(&work->flags, SLOW_WORK_EXECUTING, slow_work_wait,
 551                             TASK_UNINTERRUPTIBLE);
 552
 553         clear_bit(SLOW_WORK_CANCELLING, &work->flags);
 554         if (put)
 555                 slow_work_put_ref(work);
 556 }
 557 EXPORT_SYMBOL(slow_work_cancel);
 558
 559 /*
 560  * Handle expiry of the delay timer, indicating that a delayed slow work item
 561  * should now be queued if not cancelled
 562  */
 563 static void delayed_slow_work_timer(unsigned long data)
 564 {
 565         wait_queue_head_t *wfo_wq;
 566         struct list_head *queue;
 567         struct slow_work *work = (struct slow_work *) data;
 568         unsigned long flags;
 569         bool queued = false, put = false, first = false;
 570
 571         if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {
 572                 wfo_wq = &vslow_work_queue_waits_for_occupation;
 573                 queue = &vslow_work_queue;
 574         } else {
 575                 wfo_wq = &slow_work_queue_waits_for_occupation;
 576                 queue = &slow_work_queue;
 577         }
 578
 579         spin_lock_irqsave(&slow_work_queue_lock, flags);
 580         if (likely(!test_bit(SLOW_WORK_CANCELLING, &work->flags))) {
 581                 clear_bit(SLOW_WORK_DELAYED, &work->flags);
 582
 583                 if (test_bit(SLOW_WORK_EXECUTING, &work->flags)) {
 584                         /* we discard the reference the timer was holding in
 585                          * favour of the one the executor holds */
 586                         set_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags);
 587                         put = true;
 588                 } else {
 589                         slow_work_mark_time(work);
 590                         list_add_tail(&work->link, queue);
 591                         queued = true;
 592                         if (work->link.prev == queue)
 593                                 first = true;
 594                 }
 595         }
 596
 597         spin_unlock_irqrestore(&slow_work_queue_lock, flags);
 598         if (put)
 599                 slow_work_put_ref(work);
 600         if (first)
 601                 wake_up(wfo_wq);
 602         if (queued)
 603                 wake_up(&slow_work_thread_wq);
 604 }
 605
 606 /**
 607  * delayed_slow_work_enqueue - Schedule a delayed slow work item for processing
 608  * @dwork: The delayed work item to queue
 609  * @delay: When to start executing the work, in jiffies from now
 610  *
 611  * This is similar to slow_work_enqueue(), but it adds a delay before the work
 612  * is actually queued for processing.
 613  *
 614  * The item can have delayed processing requested on it whilst it is being
 615  * executed.  The delay will begin immediately, and if it expires before the
 616  * item finishes executing, the item will be placed back on the queue when it
 617  * has done executing.
 618  */
 619 int delayed_slow_work_enqueue(struct delayed_slow_work *dwork,
 620                               unsigned long delay)
 621 {
 622         struct slow_work *work = &dwork->work;
 623         unsigned long flags;
 624         int ret;
 625
 626         if (delay == 0)
 627                 return slow_work_enqueue(&dwork->work);
 628
 629         BUG_ON(slow_work_user_count <= 0);
 630         BUG_ON(!work);
 631         BUG_ON(!work->ops);
 632
 633         if (test_bit(SLOW_WORK_CANCELLING, &work->flags))
 634                 return -ECANCELED;
 635
 636         if (!test_and_set_bit_lock(SLOW_WORK_PENDING, &work->flags)) {
 637                 spin_lock_irqsave(&slow_work_queue_lock, flags);
 638
 639                 if (test_bit(SLOW_WORK_CANCELLING, &work->flags))
 640                         goto cancelled;
 641
 642                 /* the timer holds a reference whilst it is pending */
 643                 ret = slow_work_get_ref(work);
 644                 if (ret < 0)
 645                         goto cant_get_ref;
 646
 647                 if (test_and_set_bit(SLOW_WORK_DELAYED, &work->flags))
 648                         BUG();
 649                 dwork->timer.expires = jiffies + delay;
 650                 dwork->timer.data = (unsigned long) work;
 651                 dwork->timer.function = delayed_slow_work_timer;
 652                 add_timer(&dwork->timer);
 653
 654                 spin_unlock_irqrestore(&slow_work_queue_lock, flags);
 655         }
 656
 657         return 0;
 658
 659 cancelled:
 660         ret = -ECANCELED;
 661 cant_get_ref:
 662         spin_unlock_irqrestore(&slow_work_queue_lock, flags);
 663         return ret;
 664 }
 665 EXPORT_SYMBOL(delayed_slow_work_enqueue);
 666
 667 /*
 668  * Schedule a cull of the thread pool at some time in the near future
 669  */
 670 static void slow_work_schedule_cull(void)
 671 {
 672         mod_timer(&slow_work_cull_timer,
 673                   round_jiffies(jiffies + SLOW_WORK_CULL_TIMEOUT));
 674 }
 675
 676 /*
 677  * Worker thread culling algorithm
 678  */
 679 static bool slow_work_cull_thread(void)
 680 {
 681         unsigned long flags;
 682         bool do_cull = false;
 683
 684         spin_lock_irqsave(&slow_work_queue_lock, flags);
 685
 686         if (slow_work_cull) {
 687                 slow_work_cull = false;
 688
 689                 if (list_empty(&slow_work_queue) &&
 690                     list_empty(&vslow_work_queue) &&
 691                     atomic_read(&slow_work_thread_count) >
 692                     slow_work_min_threads) {
 693                         slow_work_schedule_cull();
 694                         do_cull = true;
 695                 }
 696         }
 697
 698         spin_unlock_irqrestore(&slow_work_queue_lock, flags);
 699         return do_cull;
 700 }
 701
 702 /*
 703  * Determine if there is slow work available for dispatch
 704  */
 705 static inline bool slow_work_available(int vsmax)
 706 {
 707         return !list_empty(&slow_work_queue) ||
 708                 (!list_empty(&vslow_work_queue) &&
 709                  atomic_read(&vslow_work_executing_count) < vsmax);
 710 }
 711
 712 /*
 713  * Worker thread dispatcher
 714  */
 715 static int slow_work_thread(void *_data)
 716 {
 717         int vsmax, id;
 718
 719         DEFINE_WAIT(wait);
 720
 721         set_freezable();
 722         set_user_nice(current, -5);
 723
 724         /* allocate ourselves an ID */
 725         spin_lock_irq(&slow_work_queue_lock);
 726         id = find_first_zero_bit(slow_work_ids, SLOW_WORK_THREAD_LIMIT);
 727         BUG_ON(id < 0 || id >= SLOW_WORK_THREAD_LIMIT);
 728         __set_bit(id, slow_work_ids);
 729         slow_work_set_thread_pid(id, current->pid);
 730         spin_unlock_irq(&slow_work_queue_lock);
 731
 732         sprintf(current->comm, "kslowd%03u", id);
 733
 734         for (;;) {
 735                 vsmax = vslow_work_proportion;
 736                 vsmax *= atomic_read(&slow_work_thread_count);
 737                 vsmax /= 100;
 738
 739                 prepare_to_wait_exclusive(&slow_work_thread_wq, &wait,
 740                                           TASK_INTERRUPTIBLE);
 741                 if (!freezing(current) &&
 742                     !slow_work_threads_should_exit &&
 743                     !slow_work_available(vsmax) &&
 744                     !slow_work_cull)
 745                         schedule();
 746                 finish_wait(&slow_work_thread_wq, &wait);
 747
 748                 try_to_freeze();
 749
 750                 vsmax = vslow_work_proportion;
 751                 vsmax *= atomic_read(&slow_work_thread_count);
 752                 vsmax /= 100;
 753
 754                 if (slow_work_available(vsmax) && slow_work_execute(id)) {
 755                         cond_resched();
 756                         if (list_empty(&slow_work_queue) &&
 757                             list_empty(&vslow_work_queue) &&
 758                             atomic_read(&slow_work_thread_count) >
 759                             slow_work_min_threads)
 760                                 slow_work_schedule_cull();
 761                         continue;
 762                 }
 763
 764                 if (slow_work_threads_should_exit)
 765                         break;
 766
 767                 if (slow_work_cull && slow_work_cull_thread())
 768                         break;
 769         }
 770
 771         spin_lock_irq(&slow_work_queue_lock);
 772         slow_work_set_thread_pid(id, 0);
 773         __clear_bit(id, slow_work_ids);
 774         spin_unlock_irq(&slow_work_queue_lock);
 775
 776         if (atomic_dec_and_test(&slow_work_thread_count))
 777                 complete_and_exit(&slow_work_last_thread_exited, 0);
 778         return 0;
 779 }
 780
 781 /*
 782  * Handle thread cull timer expiration
 783  */
 784 static void slow_work_cull_timeout(unsigned long data)
 785 {
 786         slow_work_cull = true;
 787         wake_up(&slow_work_thread_wq);
 788 }
 789
 790 /*
 791  * Start a new slow work thread
 792  */
 793 static void slow_work_new_thread_execute(struct slow_work *work)
 794 {
 795         struct task_struct *p;
 796
 797         if (slow_work_threads_should_exit)
 798                 return;
 799
 800         if (atomic_read(&slow_work_thread_count) >= slow_work_max_threads)
 801                 return;
 802
 803         if (!mutex_trylock(&slow_work_user_lock))
 804                 return;
 805
 806         slow_work_may_not_start_new_thread = true;
 807         atomic_inc(&slow_work_thread_count);
 808         p = kthread_run(slow_work_thread, NULL, "kslowd");
 809         if (IS_ERR(p)) {
 810                 printk(KERN_DEBUG "Slow work thread pool: OOM\n");
 811                 if (atomic_dec_and_test(&slow_work_thread_count))
 812                         BUG(); /* we're running on a slow work thread... */
 813                 mod_timer(&slow_work_oom_timer,
 814                           round_jiffies(jiffies + SLOW_WORK_OOM_TIMEOUT));
 815         } else {
 816                 /* ratelimit the starting of new threads */
 817                 mod_timer(&slow_work_oom_timer, jiffies + 1);
 818         }
 819
 820         mutex_unlock(&slow_work_user_lock);
 821 }
 822
 823 static const struct slow_work_ops slow_work_new_thread_ops = {
 824         .owner          = THIS_MODULE,
 825         .execute        = slow_work_new_thread_execute,
 826 #ifdef CONFIG_SLOW_WORK_DEBUG
 827         .desc           = slow_work_new_thread_desc,
 828 #endif
 829 };
 830
 831 /*
 832  * post-OOM new thread start suppression expiration
 833  */
 834 static void slow_work_oom_timeout(unsigned long data)
 835 {
 836         slow_work_may_not_start_new_thread = false;
 837 }
 838
 839 #ifdef CONFIG_SYSCTL
 840 /*
 841  * Handle adjustment of the minimum number of threads
 842  */
 843 static int slow_work_min_threads_sysctl(struct ctl_table *table, int write,
 844                                         void __user *buffer,
 845                                         size_t *lenp, loff_t *ppos)
 846 {
 847         int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 848         int n;
 849
 850         if (ret == 0) {
 851                 mutex_lock(&slow_work_user_lock);
 852                 if (slow_work_user_count > 0) {
 853                         /* see if we need to start or stop threads */
 854                         n = atomic_read(&slow_work_thread_count) -
 855                                 slow_work_min_threads;
 856
 857                         if (n < 0 && !slow_work_may_not_start_new_thread)
 858                                 slow_work_enqueue(&slow_work_new_thread);
 859                         else if (n > 0)
 860                                 slow_work_schedule_cull();
 861                 }
 862                 mutex_unlock(&slow_work_user_lock);
 863         }
 864
 865         return ret;
 866 }
 867
 868 /*
 869  * Handle adjustment of the maximum number of threads
 870  */
 871 static int slow_work_max_threads_sysctl(struct ctl_table *table, int write,
 872                                         void __user *buffer,
 873                                         size_t *lenp, loff_t *ppos)
 874 {
 875         int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 876         int n;
 877
 878         if (ret == 0) {
 879                 mutex_lock(&slow_work_user_lock);
 880                 if (slow_work_user_count > 0) {
 881                         /* see if we need to stop threads */
 882                         n = slow_work_max_threads -
 883                                 atomic_read(&slow_work_thread_count);
 884
 885                         if (n < 0)
 886                                 slow_work_schedule_cull();
 887                 }
 888                 mutex_unlock(&slow_work_user_lock);
 889         }
 890
 891         return ret;
 892 }
 893 #endif /* CONFIG_SYSCTL */
 894
 895 /**
 896  * slow_work_register_user - Register a user of the facility
 897  * @module: The module about to make use of the facility
 898  *
 899  * Register a user of the facility, starting up the initial threads if there
 900  * aren't any other users at this point.  This will return 0 if successful, or
 901  * an error if not.
 902  */
 903 int slow_work_register_user(struct module *module)
 904 {
 905         struct task_struct *p;
 906         int loop;
 907
 908         mutex_lock(&slow_work_user_lock);
 909
 910         if (slow_work_user_count == 0) {
 911                 printk(KERN_NOTICE "Slow work thread pool: Starting up\n");
 912                 init_completion(&slow_work_last_thread_exited);
 913
 914                 slow_work_threads_should_exit = false;
 915                 slow_work_init(&slow_work_new_thread,
 916                                &slow_work_new_thread_ops);
 917                 slow_work_may_not_start_new_thread = false;
 918                 slow_work_cull = false;
 919
 920                 /* start the minimum number of threads */
 921                 for (loop = 0; loop < slow_work_min_threads; loop++) {
 922                         atomic_inc(&slow_work_thread_count);
 923                         p = kthread_run(slow_work_thread, NULL, "kslowd");
 924                         if (IS_ERR(p))
 925                                 goto error;
 926                 }
 927                 printk(KERN_NOTICE "Slow work thread pool: Ready\n");
 928         }
 929
 930         slow_work_user_count++;
 931         mutex_unlock(&slow_work_user_lock);
 932         return 0;
 933
 934 error:
 935         if (atomic_dec_and_test(&slow_work_thread_count))
 936                 complete(&slow_work_last_thread_exited);
 937         if (loop > 0) {
 938                 printk(KERN_ERR "Slow work thread pool:"
 939                        " Aborting startup on ENOMEM\n");
 940                 slow_work_threads_should_exit = true;
 941                 wake_up_all(&slow_work_thread_wq);
 942                 wait_for_completion(&slow_work_last_thread_exited);
 943                 printk(KERN_ERR "Slow work thread pool: Aborted\n");
 944         }
 945         mutex_unlock(&slow_work_user_lock);
 946         return PTR_ERR(p);
 947 }
 948 EXPORT_SYMBOL(slow_work_register_user);
 949
 950 /*
 951  * wait for all outstanding items from the calling module to complete
 952  * - note that more items may be queued whilst we're waiting
 953  */
 954 static void slow_work_wait_for_items(struct module *module)
 955 {
 956 #ifdef CONFIG_MODULES
 957         DECLARE_WAITQUEUE(myself, current);
 958         struct slow_work *work;
 959         int loop;
 960
 961         mutex_lock(&slow_work_unreg_sync_lock);
 962         add_wait_queue(&slow_work_unreg_wq, &myself);
 963
 964         for (;;) {
 965                 spin_lock_irq(&slow_work_queue_lock);
 966
 967                 /* first of all, we wait for the last queued item in each list
 968                  * to be processed */
 969                 list_for_each_entry_reverse(work, &vslow_work_queue, link) {
 970                         if (work->owner == module) {
 971                                 set_current_state(TASK_UNINTERRUPTIBLE);
 972                                 slow_work_unreg_work_item = work;
 973                                 goto do_wait;
 974                         }
 975                 }
 976                 list_for_each_entry_reverse(work, &slow_work_queue, link) {
 977                         if (work->owner == module) {
 978                                 set_current_state(TASK_UNINTERRUPTIBLE);
 979                                 slow_work_unreg_work_item = work;
 980                                 goto do_wait;
 981                         }
 982                 }
 983
 984                 /* then we wait for the items being processed to finish */
 985                 slow_work_unreg_module = module;
 986                 smp_mb();
 987                 for (loop = 0; loop < SLOW_WORK_THREAD_LIMIT; loop++) {
 988                         if (slow_work_thread_processing[loop] == module)
 989                                 goto do_wait;
 990                 }
 991                 spin_unlock_irq(&slow_work_queue_lock);
 992                 break; /* okay, we're done */
 993
 994         do_wait:
 995                 spin_unlock_irq(&slow_work_queue_lock);
 996                 schedule();
 997                 slow_work_unreg_work_item = NULL;
 998                 slow_work_unreg_module = NULL;
 999         }
1000
1001         remove_wait_queue(&slow_work_unreg_wq, &myself);
1002         mutex_unlock(&slow_work_unreg_sync_lock);
1003 #endif /* CONFIG_MODULES */
1004 }
1005
1006 /**
1007  * slow_work_unregister_user - Unregister a user of the facility
1008  * @module: The module whose items should be cleared
1009  *
1010  * Unregister a user of the facility, killing all the threads if this was the
1011  * last one.
1012  *
1013  * This waits for all the work items belonging to the nominated module to go
1014  * away before proceeding.
1015  */
1016 void slow_work_unregister_user(struct module *module)
1017 {
1018         /* first of all, wait for all outstanding items from the calling module
1019          * to complete */
1020         if (module)
1021                 slow_work_wait_for_items(module);
1022
1023         /* then we can actually go about shutting down the facility if need
1024          * be */
1025         mutex_lock(&slow_work_user_lock);
1026
1027         BUG_ON(slow_work_user_count <= 0);
1028
1029         slow_work_user_count--;
1030         if (slow_work_user_count == 0) {
1031                 printk(KERN_NOTICE "Slow work thread pool: Shutting down\n");
1032                 slow_work_threads_should_exit = true;
1033                 del_timer_sync(&slow_work_cull_timer);
1034                 del_timer_sync(&slow_work_oom_timer);
1035                 wake_up_all(&slow_work_thread_wq);
1036                 wait_for_completion(&slow_work_last_thread_exited);
1037                 printk(KERN_NOTICE "Slow work thread pool:"
1038                        " Shut down complete\n");
1039         }
1040
1041         mutex_unlock(&slow_work_user_lock);
1042 }
1043 EXPORT_SYMBOL(slow_work_unregister_user);
1044
1045 /*
1046  * Initialise the slow work facility
1047  */
1048 static int __init init_slow_work(void)
1049 {
1050         unsigned nr_cpus = num_possible_cpus();
1051
1052         if (slow_work_max_threads < nr_cpus)
1053                 slow_work_max_threads = nr_cpus;
1054 #ifdef CONFIG_SYSCTL
1055         if (slow_work_max_max_threads < nr_cpus * 2)
1056                 slow_work_max_max_threads = nr_cpus * 2;
1057 #endif
1058 #ifdef CONFIG_SLOW_WORK_DEBUG
1059         {
1060                 struct dentry *dbdir;
1061
1062                 dbdir = debugfs_create_dir("slow_work", NULL);
1063                 if (dbdir && !IS_ERR(dbdir))
1064                         debugfs_create_file("runqueue", S_IFREG | 0400, dbdir,
1065                                             NULL, &slow_work_runqueue_fops);
1066         }
1067 #endif
1068         return 0;
1069 }
1070
1071 subsys_initcall(init_slow_work);