Revision 492a74f4210e15f4701422e2e1c4cd3c1e45ddae authored by Steven Rostedt on 25 January 2010, 20:17:47 UTC, committed by Steven Rostedt on 26 January 2010, 21:09:30 UTC
Usually reads of the ring buffer is performed by a single task. There are two types of reads from the ring buffer. One is a consuming read which will consume the entry that was read and the next read will be the entry that follows. The other is an iterator that will let the user read the contents of the ring buffer without modifying it. When an iterator is allocated, writes to the ring buffer are disabled to protect the iterator. The problem exists when consuming reads happen while an iterator is allocated. Specifically, the kind of read that swaps out an entire page (used by splice) and replaces it with a new read. If the iterator is on the page that is swapped out, then the next read may read from this swapped out page and return garbage. This patch adds a check when reading the iterator to make sure that the iterator contents are still valid. If a consuming read has taken place, the iterator is reset. Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
1 parent 74bf407
slow-work.c
/* Worker thread pool for slow items, such as filesystem lookups or mkdirs
*
* Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*
* See Documentation/slow-work.txt
*/
#include <linux/module.h>
#include <linux/slow-work.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/wait.h>
#include <linux/debugfs.h>
#include "slow-work.h"
static void slow_work_cull_timeout(unsigned long);
static void slow_work_oom_timeout(unsigned long);
#ifdef CONFIG_SYSCTL
static int slow_work_min_threads_sysctl(struct ctl_table *, int,
void __user *, size_t *, loff_t *);
static int slow_work_max_threads_sysctl(struct ctl_table *, int ,
void __user *, size_t *, loff_t *);
#endif
/*
* The pool of threads has at least min threads in it as long as someone is
* using the facility, and may have as many as max.
*
* A portion of the pool may be processing very slow operations.
*/
static unsigned slow_work_min_threads = 2;
static unsigned slow_work_max_threads = 4;
static unsigned vslow_work_proportion = 50; /* % of threads that may process
* very slow work */
#ifdef CONFIG_SYSCTL
static const int slow_work_min_min_threads = 2;
static int slow_work_max_max_threads = SLOW_WORK_THREAD_LIMIT;
static const int slow_work_min_vslow = 1;
static const int slow_work_max_vslow = 99;
ctl_table slow_work_sysctls[] = {
{
.procname = "min-threads",
.data = &slow_work_min_threads,
.maxlen = sizeof(unsigned),
.mode = 0644,
.proc_handler = slow_work_min_threads_sysctl,
.extra1 = (void *) &slow_work_min_min_threads,
.extra2 = &slow_work_max_threads,
},
{
.procname = "max-threads",
.data = &slow_work_max_threads,
.maxlen = sizeof(unsigned),
.mode = 0644,
.proc_handler = slow_work_max_threads_sysctl,
.extra1 = &slow_work_min_threads,
.extra2 = (void *) &slow_work_max_max_threads,
},
{
.procname = "vslow-percentage",
.data = &vslow_work_proportion,
.maxlen = sizeof(unsigned),
.mode = 0644,
.proc_handler = proc_dointvec_minmax,
.extra1 = (void *) &slow_work_min_vslow,
.extra2 = (void *) &slow_work_max_vslow,
},
{}
};
#endif
/*
* The active state of the thread pool
*/
static atomic_t slow_work_thread_count;
static atomic_t vslow_work_executing_count;
static bool slow_work_may_not_start_new_thread;
static bool slow_work_cull; /* cull a thread due to lack of activity */
static DEFINE_TIMER(slow_work_cull_timer, slow_work_cull_timeout, 0, 0);
static DEFINE_TIMER(slow_work_oom_timer, slow_work_oom_timeout, 0, 0);
static struct slow_work slow_work_new_thread; /* new thread starter */
/*
* slow work ID allocation (use slow_work_queue_lock)
*/
static DECLARE_BITMAP(slow_work_ids, SLOW_WORK_THREAD_LIMIT);
/*
* Unregistration tracking to prevent put_ref() from disappearing during module
* unload
*/
#ifdef CONFIG_MODULES
static struct module *slow_work_thread_processing[SLOW_WORK_THREAD_LIMIT];
static struct module *slow_work_unreg_module;
static struct slow_work *slow_work_unreg_work_item;
static DECLARE_WAIT_QUEUE_HEAD(slow_work_unreg_wq);
static DEFINE_MUTEX(slow_work_unreg_sync_lock);
static void slow_work_set_thread_processing(int id, struct slow_work *work)
{
if (work)
slow_work_thread_processing[id] = work->owner;
}
static void slow_work_done_thread_processing(int id, struct slow_work *work)
{
struct module *module = slow_work_thread_processing[id];
slow_work_thread_processing[id] = NULL;
smp_mb();
if (slow_work_unreg_work_item == work ||
slow_work_unreg_module == module)
wake_up_all(&slow_work_unreg_wq);
}
static void slow_work_clear_thread_processing(int id)
{
slow_work_thread_processing[id] = NULL;
}
#else
static void slow_work_set_thread_processing(int id, struct slow_work *work) {}
static void slow_work_done_thread_processing(int id, struct slow_work *work) {}
static void slow_work_clear_thread_processing(int id) {}
#endif
/*
* Data for tracking currently executing items for indication through /proc
*/
#ifdef CONFIG_SLOW_WORK_DEBUG
struct slow_work *slow_work_execs[SLOW_WORK_THREAD_LIMIT];
pid_t slow_work_pids[SLOW_WORK_THREAD_LIMIT];
DEFINE_RWLOCK(slow_work_execs_lock);
#endif
/*
* The queues of work items and the lock governing access to them. These are
* shared between all the CPUs. It doesn't make sense to have per-CPU queues
* as the number of threads bears no relation to the number of CPUs.
*
* There are two queues of work items: one for slow work items, and one for
* very slow work items.
*/
LIST_HEAD(slow_work_queue);
LIST_HEAD(vslow_work_queue);
DEFINE_SPINLOCK(slow_work_queue_lock);
/*
* The following are two wait queues that get pinged when a work item is placed
* on an empty queue. These allow work items that are hogging a thread by
* sleeping in a way that could be deferred to yield their thread and enqueue
* themselves.
*/
static DECLARE_WAIT_QUEUE_HEAD(slow_work_queue_waits_for_occupation);
static DECLARE_WAIT_QUEUE_HEAD(vslow_work_queue_waits_for_occupation);
/*
* The thread controls. A variable used to signal to the threads that they
* should exit when the queue is empty, a waitqueue used by the threads to wait
* for signals, and a completion set by the last thread to exit.
*/
static bool slow_work_threads_should_exit;
static DECLARE_WAIT_QUEUE_HEAD(slow_work_thread_wq);
static DECLARE_COMPLETION(slow_work_last_thread_exited);
/*
* The number of users of the thread pool and its lock. Whilst this is zero we
* have no threads hanging around, and when this reaches zero, we wait for all
* active or queued work items to complete and kill all the threads we do have.
*/
static int slow_work_user_count;
static DEFINE_MUTEX(slow_work_user_lock);
static inline int slow_work_get_ref(struct slow_work *work)
{
if (work->ops->get_ref)
return work->ops->get_ref(work);
return 0;
}
static inline void slow_work_put_ref(struct slow_work *work)
{
if (work->ops->put_ref)
work->ops->put_ref(work);
}
/*
* Calculate the maximum number of active threads in the pool that are
* permitted to process very slow work items.
*
* The answer is rounded up to at least 1, but may not equal or exceed the
* maximum number of the threads in the pool. This means we always have at
* least one thread that can process slow work items, and we always have at
* least one thread that won't get tied up doing so.
*/
static unsigned slow_work_calc_vsmax(void)
{
unsigned vsmax;
vsmax = atomic_read(&slow_work_thread_count) * vslow_work_proportion;
vsmax /= 100;
vsmax = max(vsmax, 1U);
return min(vsmax, slow_work_max_threads - 1);
}
/*
* Attempt to execute stuff queued on a slow thread. Return true if we managed
* it, false if there was nothing to do.
*/
static noinline bool slow_work_execute(int id)
{
struct slow_work *work = NULL;
unsigned vsmax;
bool very_slow;
vsmax = slow_work_calc_vsmax();
/* see if we can schedule a new thread to be started if we're not
* keeping up with the work */
if (!waitqueue_active(&slow_work_thread_wq) &&
(!list_empty(&slow_work_queue) || !list_empty(&vslow_work_queue)) &&
atomic_read(&slow_work_thread_count) < slow_work_max_threads &&
!slow_work_may_not_start_new_thread)
slow_work_enqueue(&slow_work_new_thread);
/* find something to execute */
spin_lock_irq(&slow_work_queue_lock);
if (!list_empty(&vslow_work_queue) &&
atomic_read(&vslow_work_executing_count) < vsmax) {
work = list_entry(vslow_work_queue.next,
struct slow_work, link);
if (test_and_set_bit_lock(SLOW_WORK_EXECUTING, &work->flags))
BUG();
list_del_init(&work->link);
atomic_inc(&vslow_work_executing_count);
very_slow = true;
} else if (!list_empty(&slow_work_queue)) {
work = list_entry(slow_work_queue.next,
struct slow_work, link);
if (test_and_set_bit_lock(SLOW_WORK_EXECUTING, &work->flags))
BUG();
list_del_init(&work->link);
very_slow = false;
} else {
very_slow = false; /* avoid the compiler warning */
}
slow_work_set_thread_processing(id, work);
if (work) {
slow_work_mark_time(work);
slow_work_begin_exec(id, work);
}
spin_unlock_irq(&slow_work_queue_lock);
if (!work)
return false;
if (!test_and_clear_bit(SLOW_WORK_PENDING, &work->flags))
BUG();
/* don't execute if the work is in the process of being cancelled */
if (!test_bit(SLOW_WORK_CANCELLING, &work->flags))
work->ops->execute(work);
if (very_slow)
atomic_dec(&vslow_work_executing_count);
clear_bit_unlock(SLOW_WORK_EXECUTING, &work->flags);
/* wake up anyone waiting for this work to be complete */
wake_up_bit(&work->flags, SLOW_WORK_EXECUTING);
slow_work_end_exec(id, work);
/* if someone tried to enqueue the item whilst we were executing it,
* then it'll be left unenqueued to avoid multiple threads trying to
* execute it simultaneously
*
* there is, however, a race between us testing the pending flag and
* getting the spinlock, and between the enqueuer setting the pending
* flag and getting the spinlock, so we use a deferral bit to tell us
* if the enqueuer got there first
*/
if (test_bit(SLOW_WORK_PENDING, &work->flags)) {
spin_lock_irq(&slow_work_queue_lock);
if (!test_bit(SLOW_WORK_EXECUTING, &work->flags) &&
test_and_clear_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags))
goto auto_requeue;
spin_unlock_irq(&slow_work_queue_lock);
}
/* sort out the race between module unloading and put_ref() */
slow_work_put_ref(work);
slow_work_done_thread_processing(id, work);
return true;
auto_requeue:
/* we must complete the enqueue operation
* - we transfer our ref on the item back to the appropriate queue
* - don't wake another thread up as we're awake already
*/
slow_work_mark_time(work);
if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags))
list_add_tail(&work->link, &vslow_work_queue);
else
list_add_tail(&work->link, &slow_work_queue);
spin_unlock_irq(&slow_work_queue_lock);
slow_work_clear_thread_processing(id);
return true;
}
/**
* slow_work_sleep_till_thread_needed - Sleep till thread needed by other work
* work: The work item under execution that wants to sleep
* _timeout: Scheduler sleep timeout
*
* Allow a requeueable work item to sleep on a slow-work processor thread until
* that thread is needed to do some other work or the sleep is interrupted by
* some other event.
*
* The caller must set up a wake up event before calling this and must have set
* the appropriate sleep mode (such as TASK_UNINTERRUPTIBLE) and tested its own
* condition before calling this function as no test is made here.
*
* False is returned if there is nothing on the queue; true is returned if the
* work item should be requeued
*/
bool slow_work_sleep_till_thread_needed(struct slow_work *work,
signed long *_timeout)
{
wait_queue_head_t *wfo_wq;
struct list_head *queue;
DEFINE_WAIT(wait);
if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {
wfo_wq = &vslow_work_queue_waits_for_occupation;
queue = &vslow_work_queue;
} else {
wfo_wq = &slow_work_queue_waits_for_occupation;
queue = &slow_work_queue;
}
if (!list_empty(queue))
return true;
add_wait_queue_exclusive(wfo_wq, &wait);
if (list_empty(queue))
*_timeout = schedule_timeout(*_timeout);
finish_wait(wfo_wq, &wait);
return !list_empty(queue);
}
EXPORT_SYMBOL(slow_work_sleep_till_thread_needed);
/**
* slow_work_enqueue - Schedule a slow work item for processing
* @work: The work item to queue
*
* Schedule a slow work item for processing. If the item is already undergoing
* execution, this guarantees not to re-enter the execution routine until the
* first execution finishes.
*
* The item is pinned by this function as it retains a reference to it, managed
* through the item operations. The item is unpinned once it has been
* executed.
*
* An item may hog the thread that is running it for a relatively large amount
* of time, sufficient, for example, to perform several lookup, mkdir, create
* and setxattr operations. It may sleep on I/O and may sleep to obtain locks.
*
* Conversely, if a number of items are awaiting processing, it may take some
* time before any given item is given attention. The number of threads in the
* pool may be increased to deal with demand, but only up to a limit.
*
* If SLOW_WORK_VERY_SLOW is set on the work item, then it will be placed in
* the very slow queue, from which only a portion of the threads will be
* allowed to pick items to execute. This ensures that very slow items won't
* overly block ones that are just ordinarily slow.
*
* Returns 0 if successful, -EAGAIN if not (or -ECANCELED if cancelled work is
* attempted queued)
*/
int slow_work_enqueue(struct slow_work *work)
{
wait_queue_head_t *wfo_wq;
struct list_head *queue;
unsigned long flags;
int ret;
if (test_bit(SLOW_WORK_CANCELLING, &work->flags))
return -ECANCELED;
BUG_ON(slow_work_user_count <= 0);
BUG_ON(!work);
BUG_ON(!work->ops);
/* when honouring an enqueue request, we only promise that we will run
* the work function in the future; we do not promise to run it once
* per enqueue request
*
* we use the PENDING bit to merge together repeat requests without
* having to disable IRQs and take the spinlock, whilst still
* maintaining our promise
*/
if (!test_and_set_bit_lock(SLOW_WORK_PENDING, &work->flags)) {
if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {
wfo_wq = &vslow_work_queue_waits_for_occupation;
queue = &vslow_work_queue;
} else {
wfo_wq = &slow_work_queue_waits_for_occupation;
queue = &slow_work_queue;
}
spin_lock_irqsave(&slow_work_queue_lock, flags);
if (unlikely(test_bit(SLOW_WORK_CANCELLING, &work->flags)))
goto cancelled;
/* we promise that we will not attempt to execute the work
* function in more than one thread simultaneously
*
* this, however, leaves us with a problem if we're asked to
* enqueue the work whilst someone is executing the work
* function as simply queueing the work immediately means that
* another thread may try executing it whilst it is already
* under execution
*
* to deal with this, we set the ENQ_DEFERRED bit instead of
* enqueueing, and the thread currently executing the work
* function will enqueue the work item when the work function
* returns and it has cleared the EXECUTING bit
*/
if (test_bit(SLOW_WORK_EXECUTING, &work->flags)) {
set_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags);
} else {
ret = slow_work_get_ref(work);
if (ret < 0)
goto failed;
slow_work_mark_time(work);
list_add_tail(&work->link, queue);
wake_up(&slow_work_thread_wq);
/* if someone who could be requeued is sleeping on a
* thread, then ask them to yield their thread */
if (work->link.prev == queue)
wake_up(wfo_wq);
}
spin_unlock_irqrestore(&slow_work_queue_lock, flags);
}
return 0;
cancelled:
ret = -ECANCELED;
failed:
spin_unlock_irqrestore(&slow_work_queue_lock, flags);
return ret;
}
EXPORT_SYMBOL(slow_work_enqueue);
static int slow_work_wait(void *word)
{
schedule();
return 0;
}
/**
* slow_work_cancel - Cancel a slow work item
* @work: The work item to cancel
*
* This function will cancel a previously enqueued work item. If we cannot
* cancel the work item, it is guarenteed to have run when this function
* returns.
*/
void slow_work_cancel(struct slow_work *work)
{
bool wait = true, put = false;
set_bit(SLOW_WORK_CANCELLING, &work->flags);
smp_mb();
/* if the work item is a delayed work item with an active timer, we
* need to wait for the timer to finish _before_ getting the spinlock,
* lest we deadlock against the timer routine
*
* the timer routine will leave DELAYED set if it notices the
* CANCELLING flag in time
*/
if (test_bit(SLOW_WORK_DELAYED, &work->flags)) {
struct delayed_slow_work *dwork =
container_of(work, struct delayed_slow_work, work);
del_timer_sync(&dwork->timer);
}
spin_lock_irq(&slow_work_queue_lock);
if (test_bit(SLOW_WORK_DELAYED, &work->flags)) {
/* the timer routine aborted or never happened, so we are left
* holding the timer's reference on the item and should just
* drop the pending flag and wait for any ongoing execution to
* finish */
struct delayed_slow_work *dwork =
container_of(work, struct delayed_slow_work, work);
BUG_ON(timer_pending(&dwork->timer));
BUG_ON(!list_empty(&work->link));
clear_bit(SLOW_WORK_DELAYED, &work->flags);
put = true;
clear_bit(SLOW_WORK_PENDING, &work->flags);
} else if (test_bit(SLOW_WORK_PENDING, &work->flags) &&
!list_empty(&work->link)) {
/* the link in the pending queue holds a reference on the item
* that we will need to release */
list_del_init(&work->link);
wait = false;
put = true;
clear_bit(SLOW_WORK_PENDING, &work->flags);
} else if (test_and_clear_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags)) {
/* the executor is holding our only reference on the item, so
* we merely need to wait for it to finish executing */
clear_bit(SLOW_WORK_PENDING, &work->flags);
}
spin_unlock_irq(&slow_work_queue_lock);
/* the EXECUTING flag is set by the executor whilst the spinlock is set
* and before the item is dequeued - so assuming the above doesn't
* actually dequeue it, simply waiting for the EXECUTING flag to be
* released here should be sufficient */
if (wait)
wait_on_bit(&work->flags, SLOW_WORK_EXECUTING, slow_work_wait,
TASK_UNINTERRUPTIBLE);
clear_bit(SLOW_WORK_CANCELLING, &work->flags);
if (put)
slow_work_put_ref(work);
}
EXPORT_SYMBOL(slow_work_cancel);
/*
* Handle expiry of the delay timer, indicating that a delayed slow work item
* should now be queued if not cancelled
*/
static void delayed_slow_work_timer(unsigned long data)
{
wait_queue_head_t *wfo_wq;
struct list_head *queue;
struct slow_work *work = (struct slow_work *) data;
unsigned long flags;
bool queued = false, put = false, first = false;
if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {
wfo_wq = &vslow_work_queue_waits_for_occupation;
queue = &vslow_work_queue;
} else {
wfo_wq = &slow_work_queue_waits_for_occupation;
queue = &slow_work_queue;
}
spin_lock_irqsave(&slow_work_queue_lock, flags);
if (likely(!test_bit(SLOW_WORK_CANCELLING, &work->flags))) {
clear_bit(SLOW_WORK_DELAYED, &work->flags);
if (test_bit(SLOW_WORK_EXECUTING, &work->flags)) {
/* we discard the reference the timer was holding in
* favour of the one the executor holds */
set_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags);
put = true;
} else {
slow_work_mark_time(work);
list_add_tail(&work->link, queue);
queued = true;
if (work->link.prev == queue)
first = true;
}
}
spin_unlock_irqrestore(&slow_work_queue_lock, flags);
if (put)
slow_work_put_ref(work);
if (first)
wake_up(wfo_wq);
if (queued)
wake_up(&slow_work_thread_wq);
}
/**
* delayed_slow_work_enqueue - Schedule a delayed slow work item for processing
* @dwork: The delayed work item to queue
* @delay: When to start executing the work, in jiffies from now
*
* This is similar to slow_work_enqueue(), but it adds a delay before the work
* is actually queued for processing.
*
* The item can have delayed processing requested on it whilst it is being
* executed. The delay will begin immediately, and if it expires before the
* item finishes executing, the item will be placed back on the queue when it
* has done executing.
*/
int delayed_slow_work_enqueue(struct delayed_slow_work *dwork,
unsigned long delay)
{
struct slow_work *work = &dwork->work;
unsigned long flags;
int ret;
if (delay == 0)
return slow_work_enqueue(&dwork->work);
BUG_ON(slow_work_user_count <= 0);
BUG_ON(!work);
BUG_ON(!work->ops);
if (test_bit(SLOW_WORK_CANCELLING, &work->flags))
return -ECANCELED;
if (!test_and_set_bit_lock(SLOW_WORK_PENDING, &work->flags)) {
spin_lock_irqsave(&slow_work_queue_lock, flags);
if (test_bit(SLOW_WORK_CANCELLING, &work->flags))
goto cancelled;
/* the timer holds a reference whilst it is pending */
ret = work->ops->get_ref(work);
if (ret < 0)
goto cant_get_ref;
if (test_and_set_bit(SLOW_WORK_DELAYED, &work->flags))
BUG();
dwork->timer.expires = jiffies + delay;
dwork->timer.data = (unsigned long) work;
dwork->timer.function = delayed_slow_work_timer;
add_timer(&dwork->timer);
spin_unlock_irqrestore(&slow_work_queue_lock, flags);
}
return 0;
cancelled:
ret = -ECANCELED;
cant_get_ref:
spin_unlock_irqrestore(&slow_work_queue_lock, flags);
return ret;
}
EXPORT_SYMBOL(delayed_slow_work_enqueue);
/*
* Schedule a cull of the thread pool at some time in the near future
*/
static void slow_work_schedule_cull(void)
{
mod_timer(&slow_work_cull_timer,
round_jiffies(jiffies + SLOW_WORK_CULL_TIMEOUT));
}
/*
* Worker thread culling algorithm
*/
static bool slow_work_cull_thread(void)
{
unsigned long flags;
bool do_cull = false;
spin_lock_irqsave(&slow_work_queue_lock, flags);
if (slow_work_cull) {
slow_work_cull = false;
if (list_empty(&slow_work_queue) &&
list_empty(&vslow_work_queue) &&
atomic_read(&slow_work_thread_count) >
slow_work_min_threads) {
slow_work_schedule_cull();
do_cull = true;
}
}
spin_unlock_irqrestore(&slow_work_queue_lock, flags);
return do_cull;
}
/*
* Determine if there is slow work available for dispatch
*/
static inline bool slow_work_available(int vsmax)
{
return !list_empty(&slow_work_queue) ||
(!list_empty(&vslow_work_queue) &&
atomic_read(&vslow_work_executing_count) < vsmax);
}
/*
* Worker thread dispatcher
*/
static int slow_work_thread(void *_data)
{
int vsmax, id;
DEFINE_WAIT(wait);
set_freezable();
set_user_nice(current, -5);
/* allocate ourselves an ID */
spin_lock_irq(&slow_work_queue_lock);
id = find_first_zero_bit(slow_work_ids, SLOW_WORK_THREAD_LIMIT);
BUG_ON(id < 0 || id >= SLOW_WORK_THREAD_LIMIT);
__set_bit(id, slow_work_ids);
slow_work_set_thread_pid(id, current->pid);
spin_unlock_irq(&slow_work_queue_lock);
sprintf(current->comm, "kslowd%03u", id);
for (;;) {
vsmax = vslow_work_proportion;
vsmax *= atomic_read(&slow_work_thread_count);
vsmax /= 100;
prepare_to_wait_exclusive(&slow_work_thread_wq, &wait,
TASK_INTERRUPTIBLE);
if (!freezing(current) &&
!slow_work_threads_should_exit &&
!slow_work_available(vsmax) &&
!slow_work_cull)
schedule();
finish_wait(&slow_work_thread_wq, &wait);
try_to_freeze();
vsmax = vslow_work_proportion;
vsmax *= atomic_read(&slow_work_thread_count);
vsmax /= 100;
if (slow_work_available(vsmax) && slow_work_execute(id)) {
cond_resched();
if (list_empty(&slow_work_queue) &&
list_empty(&vslow_work_queue) &&
atomic_read(&slow_work_thread_count) >
slow_work_min_threads)
slow_work_schedule_cull();
continue;
}
if (slow_work_threads_should_exit)
break;
if (slow_work_cull && slow_work_cull_thread())
break;
}
spin_lock_irq(&slow_work_queue_lock);
slow_work_set_thread_pid(id, 0);
__clear_bit(id, slow_work_ids);
spin_unlock_irq(&slow_work_queue_lock);
if (atomic_dec_and_test(&slow_work_thread_count))
complete_and_exit(&slow_work_last_thread_exited, 0);
return 0;
}
/*
* Handle thread cull timer expiration
*/
static void slow_work_cull_timeout(unsigned long data)
{
slow_work_cull = true;
wake_up(&slow_work_thread_wq);
}
/*
* Start a new slow work thread
*/
static void slow_work_new_thread_execute(struct slow_work *work)
{
struct task_struct *p;
if (slow_work_threads_should_exit)
return;
if (atomic_read(&slow_work_thread_count) >= slow_work_max_threads)
return;
if (!mutex_trylock(&slow_work_user_lock))
return;
slow_work_may_not_start_new_thread = true;
atomic_inc(&slow_work_thread_count);
p = kthread_run(slow_work_thread, NULL, "kslowd");
if (IS_ERR(p)) {
printk(KERN_DEBUG "Slow work thread pool: OOM\n");
if (atomic_dec_and_test(&slow_work_thread_count))
BUG(); /* we're running on a slow work thread... */
mod_timer(&slow_work_oom_timer,
round_jiffies(jiffies + SLOW_WORK_OOM_TIMEOUT));
} else {
/* ratelimit the starting of new threads */
mod_timer(&slow_work_oom_timer, jiffies + 1);
}
mutex_unlock(&slow_work_user_lock);
}
static const struct slow_work_ops slow_work_new_thread_ops = {
.owner = THIS_MODULE,
.execute = slow_work_new_thread_execute,
#ifdef CONFIG_SLOW_WORK_DEBUG
.desc = slow_work_new_thread_desc,
#endif
};
/*
* post-OOM new thread start suppression expiration
*/
static void slow_work_oom_timeout(unsigned long data)
{
slow_work_may_not_start_new_thread = false;
}
#ifdef CONFIG_SYSCTL
/*
* Handle adjustment of the minimum number of threads
*/
static int slow_work_min_threads_sysctl(struct ctl_table *table, int write,
void __user *buffer,
size_t *lenp, loff_t *ppos)
{
int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
int n;
if (ret == 0) {
mutex_lock(&slow_work_user_lock);
if (slow_work_user_count > 0) {
/* see if we need to start or stop threads */
n = atomic_read(&slow_work_thread_count) -
slow_work_min_threads;
if (n < 0 && !slow_work_may_not_start_new_thread)
slow_work_enqueue(&slow_work_new_thread);
else if (n > 0)
slow_work_schedule_cull();
}
mutex_unlock(&slow_work_user_lock);
}
return ret;
}
/*
* Handle adjustment of the maximum number of threads
*/
static int slow_work_max_threads_sysctl(struct ctl_table *table, int write,
void __user *buffer,
size_t *lenp, loff_t *ppos)
{
int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
int n;
if (ret == 0) {
mutex_lock(&slow_work_user_lock);
if (slow_work_user_count > 0) {
/* see if we need to stop threads */
n = slow_work_max_threads -
atomic_read(&slow_work_thread_count);
if (n < 0)
slow_work_schedule_cull();
}
mutex_unlock(&slow_work_user_lock);
}
return ret;
}
#endif /* CONFIG_SYSCTL */
/**
* slow_work_register_user - Register a user of the facility
* @module: The module about to make use of the facility
*
* Register a user of the facility, starting up the initial threads if there
* aren't any other users at this point. This will return 0 if successful, or
* an error if not.
*/
int slow_work_register_user(struct module *module)
{
struct task_struct *p;
int loop;
mutex_lock(&slow_work_user_lock);
if (slow_work_user_count == 0) {
printk(KERN_NOTICE "Slow work thread pool: Starting up\n");
init_completion(&slow_work_last_thread_exited);
slow_work_threads_should_exit = false;
slow_work_init(&slow_work_new_thread,
&slow_work_new_thread_ops);
slow_work_may_not_start_new_thread = false;
slow_work_cull = false;
/* start the minimum number of threads */
for (loop = 0; loop < slow_work_min_threads; loop++) {
atomic_inc(&slow_work_thread_count);
p = kthread_run(slow_work_thread, NULL, "kslowd");
if (IS_ERR(p))
goto error;
}
printk(KERN_NOTICE "Slow work thread pool: Ready\n");
}
slow_work_user_count++;
mutex_unlock(&slow_work_user_lock);
return 0;
error:
if (atomic_dec_and_test(&slow_work_thread_count))
complete(&slow_work_last_thread_exited);
if (loop > 0) {
printk(KERN_ERR "Slow work thread pool:"
" Aborting startup on ENOMEM\n");
slow_work_threads_should_exit = true;
wake_up_all(&slow_work_thread_wq);
wait_for_completion(&slow_work_last_thread_exited);
printk(KERN_ERR "Slow work thread pool: Aborted\n");
}
mutex_unlock(&slow_work_user_lock);
return PTR_ERR(p);
}
EXPORT_SYMBOL(slow_work_register_user);
/*
* wait for all outstanding items from the calling module to complete
* - note that more items may be queued whilst we're waiting
*/
static void slow_work_wait_for_items(struct module *module)
{
#ifdef CONFIG_MODULES
DECLARE_WAITQUEUE(myself, current);
struct slow_work *work;
int loop;
mutex_lock(&slow_work_unreg_sync_lock);
add_wait_queue(&slow_work_unreg_wq, &myself);
for (;;) {
spin_lock_irq(&slow_work_queue_lock);
/* first of all, we wait for the last queued item in each list
* to be processed */
list_for_each_entry_reverse(work, &vslow_work_queue, link) {
if (work->owner == module) {
set_current_state(TASK_UNINTERRUPTIBLE);
slow_work_unreg_work_item = work;
goto do_wait;
}
}
list_for_each_entry_reverse(work, &slow_work_queue, link) {
if (work->owner == module) {
set_current_state(TASK_UNINTERRUPTIBLE);
slow_work_unreg_work_item = work;
goto do_wait;
}
}
/* then we wait for the items being processed to finish */
slow_work_unreg_module = module;
smp_mb();
for (loop = 0; loop < SLOW_WORK_THREAD_LIMIT; loop++) {
if (slow_work_thread_processing[loop] == module)
goto do_wait;
}
spin_unlock_irq(&slow_work_queue_lock);
break; /* okay, we're done */
do_wait:
spin_unlock_irq(&slow_work_queue_lock);
schedule();
slow_work_unreg_work_item = NULL;
slow_work_unreg_module = NULL;
}
remove_wait_queue(&slow_work_unreg_wq, &myself);
mutex_unlock(&slow_work_unreg_sync_lock);
#endif /* CONFIG_MODULES */
}
/**
* slow_work_unregister_user - Unregister a user of the facility
* @module: The module whose items should be cleared
*
* Unregister a user of the facility, killing all the threads if this was the
* last one.
*
* This waits for all the work items belonging to the nominated module to go
* away before proceeding.
*/
void slow_work_unregister_user(struct module *module)
{
/* first of all, wait for all outstanding items from the calling module
* to complete */
if (module)
slow_work_wait_for_items(module);
/* then we can actually go about shutting down the facility if need
* be */
mutex_lock(&slow_work_user_lock);
BUG_ON(slow_work_user_count <= 0);
slow_work_user_count--;
if (slow_work_user_count == 0) {
printk(KERN_NOTICE "Slow work thread pool: Shutting down\n");
slow_work_threads_should_exit = true;
del_timer_sync(&slow_work_cull_timer);
del_timer_sync(&slow_work_oom_timer);
wake_up_all(&slow_work_thread_wq);
wait_for_completion(&slow_work_last_thread_exited);
printk(KERN_NOTICE "Slow work thread pool:"
" Shut down complete\n");
}
mutex_unlock(&slow_work_user_lock);
}
EXPORT_SYMBOL(slow_work_unregister_user);
/*
* Initialise the slow work facility
*/
static int __init init_slow_work(void)
{
unsigned nr_cpus = num_possible_cpus();
if (slow_work_max_threads < nr_cpus)
slow_work_max_threads = nr_cpus;
#ifdef CONFIG_SYSCTL
if (slow_work_max_max_threads < nr_cpus * 2)
slow_work_max_max_threads = nr_cpus * 2;
#endif
#ifdef CONFIG_SLOW_WORK_DEBUG
{
struct dentry *dbdir;
dbdir = debugfs_create_dir("slow_work", NULL);
if (dbdir && !IS_ERR(dbdir))
debugfs_create_file("runqueue", S_IFREG | 0400, dbdir,
NULL, &slow_work_runqueue_fops);
}
#endif
return 0;
}
subsys_initcall(init_slow_work);
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