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authorChris Mason <chris.mason@oracle.com>2009-09-15 20:02:33 -0400
committerChris Mason <chris.mason@oracle.com>2009-09-15 20:20:17 -0400
commit6e74057c4686dc12ea767b4bdc50a63876056e1c (patch)
treee7c70b8e08ab9e5363be28bcbcc72348122ae6e4
parent627e421a3f35ad6b52dc58982fb6f8a97c30dcd7 (diff)
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>
-rw-r--r--fs/btrfs/async-thread.c16
1 files changed, 10 insertions, 6 deletions
diff --git a/fs/btrfs/async-thread.c b/fs/btrfs/async-thread.c
index 80e33bc96c8..282ca085c2f 100644
--- a/fs/btrfs/async-thread.c
+++ b/fs/btrfs/async-thread.c
@@ -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);
/*