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Btrfs: Fix async thread shutdown race 

It was possible for an async worker thread to be selected to
receive a new work item, but exit before the work item was
actually placed into that thread's work list.

This commit fixes the race by incrementing the num_pending
counter earlier, and making sure to check the number of pending
work items before a thread exits.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Chris Mason 2009-09-15 20:02:33 -04:00
parent 627e421a3f
commit 6e74057c46
1 changed files with 10 additions and 6 deletions
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16
fs/btrfs/async-thread.c
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@ -191,7 +191,8 @@ static int try_worker_shutdown(struct btrfs_worker_thread *worker)
!worker->working &&
!list_empty(&worker->worker_list) &&
list_empty(&worker->prio_pending) &&
list_empty(&worker->pending)) {
list_empty(&worker->pending) &&
atomic_read(&worker->num_pending) == 0) {
freeit = 1;
list_del_init(&worker->worker_list);
worker->workers->num_workers--;
@ -485,7 +486,6 @@ static struct btrfs_worker_thread *next_worker(struct btrfs_workers *workers)
*/
next = workers->worker_list.next;
worker = list_entry(next, struct btrfs_worker_thread, worker_list);
atomic_inc(&worker->num_pending);
worker->sequence++;
if (worker->sequence % workers->idle_thresh == 0)
@ -521,8 +521,7 @@ again:
goto again;
}
}
spin_unlock_irqrestore(&workers->lock, flags);
return worker;
goto found;
fallback:
fallback = NULL;
@ -537,6 +536,12 @@ fallback:
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;
}
@ -569,7 +574,7 @@ int btrfs_requeue_work(struct btrfs_work *work)
spin_lock(&worker->workers->lock);
worker->idle = 0;
list_move_tail(&worker->worker_list,
&worker->workers->worker_list);
&worker->workers->worker_list);
spin_unlock(&worker->workers->lock);
}
if (!worker->working) {
@ -627,7 +632,6 @@ int btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work)
list_add_tail(&work->list, &worker->prio_pending);
else
list_add_tail(&work->list, &worker->pending);
atomic_inc(&worker->num_pending);
check_busy_worker(worker);
/*