android_kernel_xiaomi_sm8350/fs/btrfs/async-thread.c
Chris Mason 61d92c328c Btrfs: fix deadlock on async thread startup
The btrfs async worker threads are used for a wide variety of things,
including processing bio end_io functions.  This means that when
the endio threads aren't running, the rest of the FS isn't
able to do the final processing required to clear PageWriteback.

The endio threads also try to exit as they become idle and
start more as the work piles up.  The problem is that starting more
threads means kthreadd may need to allocate ram, and that allocation
may wait until the global number of writeback pages on the system is
below a certain limit.

The result of that throttling is that end IO threads wait on
kthreadd, who is waiting on IO to end, which will never happen.

This commit fixes the deadlock by handing off thread startup to a
dedicated thread.  It also fixes a bug where the on-demand thread
creation was creating far too many threads because it didn't take into
account threads being started by other procs.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
2009-10-05 09:44:45 -04:00

717 lines
18 KiB
C

/*
* Copyright (C) 2007 Oracle. All rights reserved.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public
* License v2 as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public
* License along with this program; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 021110-1307, USA.
*/
#include <linux/kthread.h>
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/freezer.h>
#include "async-thread.h"
#define WORK_QUEUED_BIT 0
#define WORK_DONE_BIT 1
#define WORK_ORDER_DONE_BIT 2
#define WORK_HIGH_PRIO_BIT 3
/*
* container for the kthread task pointer and the list of pending work
* One of these is allocated per thread.
*/
struct btrfs_worker_thread {
/* pool we belong to */
struct btrfs_workers *workers;
/* list of struct btrfs_work that are waiting for service */
struct list_head pending;
struct list_head prio_pending;
/* list of worker threads from struct btrfs_workers */
struct list_head worker_list;
/* kthread */
struct task_struct *task;
/* number of things on the pending list */
atomic_t num_pending;
/* reference counter for this struct */
atomic_t refs;
unsigned long sequence;
/* protects the pending list. */
spinlock_t lock;
/* set to non-zero when this thread is already awake and kicking */
int working;
/* are we currently idle */
int idle;
};
/*
* btrfs_start_workers uses kthread_run, which can block waiting for memory
* for a very long time. It will actually throttle on page writeback,
* and so it may not make progress until after our btrfs worker threads
* process all of the pending work structs in their queue
*
* This means we can't use btrfs_start_workers from inside a btrfs worker
* thread that is used as part of cleaning dirty memory, which pretty much
* involves all of the worker threads.
*
* Instead we have a helper queue who never has more than one thread
* where we scheduler thread start operations. This worker_start struct
* is used to contain the work and hold a pointer to the queue that needs
* another worker.
*/
struct worker_start {
struct btrfs_work work;
struct btrfs_workers *queue;
};
static void start_new_worker_func(struct btrfs_work *work)
{
struct worker_start *start;
start = container_of(work, struct worker_start, work);
btrfs_start_workers(start->queue, 1);
kfree(start);
}
static int start_new_worker(struct btrfs_workers *queue)
{
struct worker_start *start;
int ret;
start = kzalloc(sizeof(*start), GFP_NOFS);
if (!start)
return -ENOMEM;
start->work.func = start_new_worker_func;
start->queue = queue;
ret = btrfs_queue_worker(queue->atomic_worker_start, &start->work);
if (ret)
kfree(start);
return ret;
}
/*
* helper function to move a thread onto the idle list after it
* has finished some requests.
*/
static void check_idle_worker(struct btrfs_worker_thread *worker)
{
if (!worker->idle && atomic_read(&worker->num_pending) <
worker->workers->idle_thresh / 2) {
unsigned long flags;
spin_lock_irqsave(&worker->workers->lock, flags);
worker->idle = 1;
/* the list may be empty if the worker is just starting */
if (!list_empty(&worker->worker_list)) {
list_move(&worker->worker_list,
&worker->workers->idle_list);
}
spin_unlock_irqrestore(&worker->workers->lock, flags);
}
}
/*
* helper function to move a thread off the idle list after new
* pending work is added.
*/
static void check_busy_worker(struct btrfs_worker_thread *worker)
{
if (worker->idle && atomic_read(&worker->num_pending) >=
worker->workers->idle_thresh) {
unsigned long flags;
spin_lock_irqsave(&worker->workers->lock, flags);
worker->idle = 0;
if (!list_empty(&worker->worker_list)) {
list_move_tail(&worker->worker_list,
&worker->workers->worker_list);
}
spin_unlock_irqrestore(&worker->workers->lock, flags);
}
}
static void check_pending_worker_creates(struct btrfs_worker_thread *worker)
{
struct btrfs_workers *workers = worker->workers;
unsigned long flags;
rmb();
if (!workers->atomic_start_pending)
return;
spin_lock_irqsave(&workers->lock, flags);
if (!workers->atomic_start_pending)
goto out;
workers->atomic_start_pending = 0;
if (workers->num_workers + workers->num_workers_starting >=
workers->max_workers)
goto out;
workers->num_workers_starting += 1;
spin_unlock_irqrestore(&workers->lock, flags);
start_new_worker(workers);
return;
out:
spin_unlock_irqrestore(&workers->lock, flags);
}
static noinline int run_ordered_completions(struct btrfs_workers *workers,
struct btrfs_work *work)
{
if (!workers->ordered)
return 0;
set_bit(WORK_DONE_BIT, &work->flags);
spin_lock(&workers->order_lock);
while (1) {
if (!list_empty(&workers->prio_order_list)) {
work = list_entry(workers->prio_order_list.next,
struct btrfs_work, order_list);
} else if (!list_empty(&workers->order_list)) {
work = list_entry(workers->order_list.next,
struct btrfs_work, order_list);
} else {
break;
}
if (!test_bit(WORK_DONE_BIT, &work->flags))
break;
/* we are going to call the ordered done function, but
* we leave the work item on the list as a barrier so
* that later work items that are done don't have their
* functions called before this one returns
*/
if (test_and_set_bit(WORK_ORDER_DONE_BIT, &work->flags))
break;
spin_unlock(&workers->order_lock);
work->ordered_func(work);
/* now take the lock again and call the freeing code */
spin_lock(&workers->order_lock);
list_del(&work->order_list);
work->ordered_free(work);
}
spin_unlock(&workers->order_lock);
return 0;
}
static void put_worker(struct btrfs_worker_thread *worker)
{
if (atomic_dec_and_test(&worker->refs))
kfree(worker);
}
static int try_worker_shutdown(struct btrfs_worker_thread *worker)
{
int freeit = 0;
spin_lock_irq(&worker->lock);
spin_lock(&worker->workers->lock);
if (worker->workers->num_workers > 1 &&
worker->idle &&
!worker->working &&
!list_empty(&worker->worker_list) &&
list_empty(&worker->prio_pending) &&
list_empty(&worker->pending) &&
atomic_read(&worker->num_pending) == 0) {
freeit = 1;
list_del_init(&worker->worker_list);
worker->workers->num_workers--;
}
spin_unlock(&worker->workers->lock);
spin_unlock_irq(&worker->lock);
if (freeit)
put_worker(worker);
return freeit;
}
static struct btrfs_work *get_next_work(struct btrfs_worker_thread *worker,
struct list_head *prio_head,
struct list_head *head)
{
struct btrfs_work *work = NULL;
struct list_head *cur = NULL;
if(!list_empty(prio_head))
cur = prio_head->next;
smp_mb();
if (!list_empty(&worker->prio_pending))
goto refill;
if (!list_empty(head))
cur = head->next;
if (cur)
goto out;
refill:
spin_lock_irq(&worker->lock);
list_splice_tail_init(&worker->prio_pending, prio_head);
list_splice_tail_init(&worker->pending, head);
if (!list_empty(prio_head))
cur = prio_head->next;
else if (!list_empty(head))
cur = head->next;
spin_unlock_irq(&worker->lock);
if (!cur)
goto out_fail;
out:
work = list_entry(cur, struct btrfs_work, list);
out_fail:
return work;
}
/*
* main loop for servicing work items
*/
static int worker_loop(void *arg)
{
struct btrfs_worker_thread *worker = arg;
struct list_head head;
struct list_head prio_head;
struct btrfs_work *work;
INIT_LIST_HEAD(&head);
INIT_LIST_HEAD(&prio_head);
do {
again:
while (1) {
work = get_next_work(worker, &prio_head, &head);
if (!work)
break;
list_del(&work->list);
clear_bit(WORK_QUEUED_BIT, &work->flags);
work->worker = worker;
work->func(work);
atomic_dec(&worker->num_pending);
/*
* unless this is an ordered work queue,
* 'work' was probably freed by func above.
*/
run_ordered_completions(worker->workers, work);
check_pending_worker_creates(worker);
}
spin_lock_irq(&worker->lock);
check_idle_worker(worker);
if (freezing(current)) {
worker->working = 0;
spin_unlock_irq(&worker->lock);
refrigerator();
} else {
spin_unlock_irq(&worker->lock);
if (!kthread_should_stop()) {
cpu_relax();
/*
* we've dropped the lock, did someone else
* jump_in?
*/
smp_mb();
if (!list_empty(&worker->pending) ||
!list_empty(&worker->prio_pending))
continue;
/*
* this short schedule allows more work to
* come in without the queue functions
* needing to go through wake_up_process()
*
* worker->working is still 1, so nobody
* is going to try and wake us up
*/
schedule_timeout(1);
smp_mb();
if (!list_empty(&worker->pending) ||
!list_empty(&worker->prio_pending))
continue;
if (kthread_should_stop())
break;
/* still no more work?, sleep for real */
spin_lock_irq(&worker->lock);
set_current_state(TASK_INTERRUPTIBLE);
if (!list_empty(&worker->pending) ||
!list_empty(&worker->prio_pending)) {
spin_unlock_irq(&worker->lock);
goto again;
}
/*
* this makes sure we get a wakeup when someone
* adds something new to the queue
*/
worker->working = 0;
spin_unlock_irq(&worker->lock);
if (!kthread_should_stop()) {
schedule_timeout(HZ * 120);
if (!worker->working &&
try_worker_shutdown(worker)) {
return 0;
}
}
}
__set_current_state(TASK_RUNNING);
}
} while (!kthread_should_stop());
return 0;
}
/*
* this will wait for all the worker threads to shutdown
*/
int btrfs_stop_workers(struct btrfs_workers *workers)
{
struct list_head *cur;
struct btrfs_worker_thread *worker;
int can_stop;
spin_lock_irq(&workers->lock);
list_splice_init(&workers->idle_list, &workers->worker_list);
while (!list_empty(&workers->worker_list)) {
cur = workers->worker_list.next;
worker = list_entry(cur, struct btrfs_worker_thread,
worker_list);
atomic_inc(&worker->refs);
workers->num_workers -= 1;
if (!list_empty(&worker->worker_list)) {
list_del_init(&worker->worker_list);
put_worker(worker);
can_stop = 1;
} else
can_stop = 0;
spin_unlock_irq(&workers->lock);
if (can_stop)
kthread_stop(worker->task);
spin_lock_irq(&workers->lock);
put_worker(worker);
}
spin_unlock_irq(&workers->lock);
return 0;
}
/*
* simple init on struct btrfs_workers
*/
void btrfs_init_workers(struct btrfs_workers *workers, char *name, int max,
struct btrfs_workers *async_helper)
{
workers->num_workers = 0;
workers->num_workers_starting = 0;
INIT_LIST_HEAD(&workers->worker_list);
INIT_LIST_HEAD(&workers->idle_list);
INIT_LIST_HEAD(&workers->order_list);
INIT_LIST_HEAD(&workers->prio_order_list);
spin_lock_init(&workers->lock);
spin_lock_init(&workers->order_lock);
workers->max_workers = max;
workers->idle_thresh = 32;
workers->name = name;
workers->ordered = 0;
workers->atomic_start_pending = 0;
workers->atomic_worker_start = async_helper;
}
/*
* starts new worker threads. This does not enforce the max worker
* count in case you need to temporarily go past it.
*/
static int __btrfs_start_workers(struct btrfs_workers *workers,
int num_workers)
{
struct btrfs_worker_thread *worker;
int ret = 0;
int i;
for (i = 0; i < num_workers; i++) {
worker = kzalloc(sizeof(*worker), GFP_NOFS);
if (!worker) {
ret = -ENOMEM;
goto fail;
}
INIT_LIST_HEAD(&worker->pending);
INIT_LIST_HEAD(&worker->prio_pending);
INIT_LIST_HEAD(&worker->worker_list);
spin_lock_init(&worker->lock);
atomic_set(&worker->num_pending, 0);
atomic_set(&worker->refs, 1);
worker->workers = workers;
worker->task = kthread_run(worker_loop, worker,
"btrfs-%s-%d", workers->name,
workers->num_workers + i);
if (IS_ERR(worker->task)) {
ret = PTR_ERR(worker->task);
kfree(worker);
goto fail;
}
spin_lock_irq(&workers->lock);
list_add_tail(&worker->worker_list, &workers->idle_list);
worker->idle = 1;
workers->num_workers++;
workers->num_workers_starting--;
WARN_ON(workers->num_workers_starting < 0);
spin_unlock_irq(&workers->lock);
}
return 0;
fail:
btrfs_stop_workers(workers);
return ret;
}
int btrfs_start_workers(struct btrfs_workers *workers, int num_workers)
{
spin_lock_irq(&workers->lock);
workers->num_workers_starting += num_workers;
spin_unlock_irq(&workers->lock);
return __btrfs_start_workers(workers, num_workers);
}
/*
* run through the list and find a worker thread that doesn't have a lot
* to do right now. This can return null if we aren't yet at the thread
* count limit and all of the threads are busy.
*/
static struct btrfs_worker_thread *next_worker(struct btrfs_workers *workers)
{
struct btrfs_worker_thread *worker;
struct list_head *next;
int enforce_min;
enforce_min = (workers->num_workers + workers->num_workers_starting) <
workers->max_workers;
/*
* if we find an idle thread, don't move it to the end of the
* idle list. This improves the chance that the next submission
* will reuse the same thread, and maybe catch it while it is still
* working
*/
if (!list_empty(&workers->idle_list)) {
next = workers->idle_list.next;
worker = list_entry(next, struct btrfs_worker_thread,
worker_list);
return worker;
}
if (enforce_min || list_empty(&workers->worker_list))
return NULL;
/*
* if we pick a busy task, move the task to the end of the list.
* hopefully this will keep things somewhat evenly balanced.
* Do the move in batches based on the sequence number. This groups
* requests submitted at roughly the same time onto the same worker.
*/
next = workers->worker_list.next;
worker = list_entry(next, struct btrfs_worker_thread, worker_list);
worker->sequence++;
if (worker->sequence % workers->idle_thresh == 0)
list_move_tail(next, &workers->worker_list);
return worker;
}
/*
* selects a worker thread to take the next job. This will either find
* an idle worker, start a new worker up to the max count, or just return
* one of the existing busy workers.
*/
static struct btrfs_worker_thread *find_worker(struct btrfs_workers *workers)
{
struct btrfs_worker_thread *worker;
unsigned long flags;
struct list_head *fallback;
again:
spin_lock_irqsave(&workers->lock, flags);
worker = next_worker(workers);
if (!worker) {
if (workers->num_workers + workers->num_workers_starting >=
workers->max_workers) {
goto fallback;
} else if (workers->atomic_worker_start) {
workers->atomic_start_pending = 1;
goto fallback;
} else {
workers->num_workers_starting++;
spin_unlock_irqrestore(&workers->lock, flags);
/* we're below the limit, start another worker */
__btrfs_start_workers(workers, 1);
goto again;
}
}
goto found;
fallback:
fallback = NULL;
/*
* we have failed to find any workers, just
* return the first one we can find.
*/
if (!list_empty(&workers->worker_list))
fallback = workers->worker_list.next;
if (!list_empty(&workers->idle_list))
fallback = workers->idle_list.next;
BUG_ON(!fallback);
worker = list_entry(fallback,
struct btrfs_worker_thread, worker_list);
found:
/*
* this makes sure the worker doesn't exit before it is placed
* onto a busy/idle list
*/
atomic_inc(&worker->num_pending);
spin_unlock_irqrestore(&workers->lock, flags);
return worker;
}
/*
* btrfs_requeue_work just puts the work item back on the tail of the list
* it was taken from. It is intended for use with long running work functions
* that make some progress and want to give the cpu up for others.
*/
int btrfs_requeue_work(struct btrfs_work *work)
{
struct btrfs_worker_thread *worker = work->worker;
unsigned long flags;
int wake = 0;
if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
goto out;
spin_lock_irqsave(&worker->lock, flags);
if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags))
list_add_tail(&work->list, &worker->prio_pending);
else
list_add_tail(&work->list, &worker->pending);
atomic_inc(&worker->num_pending);
/* by definition we're busy, take ourselves off the idle
* list
*/
if (worker->idle) {
spin_lock(&worker->workers->lock);
worker->idle = 0;
list_move_tail(&worker->worker_list,
&worker->workers->worker_list);
spin_unlock(&worker->workers->lock);
}
if (!worker->working) {
wake = 1;
worker->working = 1;
}
if (wake)
wake_up_process(worker->task);
spin_unlock_irqrestore(&worker->lock, flags);
out:
return 0;
}
void btrfs_set_work_high_prio(struct btrfs_work *work)
{
set_bit(WORK_HIGH_PRIO_BIT, &work->flags);
}
/*
* places a struct btrfs_work into the pending queue of one of the kthreads
*/
int btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work)
{
struct btrfs_worker_thread *worker;
unsigned long flags;
int wake = 0;
/* don't requeue something already on a list */
if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
goto out;
worker = find_worker(workers);
if (workers->ordered) {
/*
* you're not allowed to do ordered queues from an
* interrupt handler
*/
spin_lock(&workers->order_lock);
if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags)) {
list_add_tail(&work->order_list,
&workers->prio_order_list);
} else {
list_add_tail(&work->order_list, &workers->order_list);
}
spin_unlock(&workers->order_lock);
} else {
INIT_LIST_HEAD(&work->order_list);
}
spin_lock_irqsave(&worker->lock, flags);
if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags))
list_add_tail(&work->list, &worker->prio_pending);
else
list_add_tail(&work->list, &worker->pending);
check_busy_worker(worker);
/*
* avoid calling into wake_up_process if this thread has already
* been kicked
*/
if (!worker->working)
wake = 1;
worker->working = 1;
if (wake)
wake_up_process(worker->task);
spin_unlock_irqrestore(&worker->lock, flags);
out:
return 0;
}