From: Chris Mason Date: Tue, 15 Sep 2009 23:57:42 +0000 (-0400) Subject: Btrfs: fix async worker startup race X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=3e99d8eb347c93a5d38081380b8c9e69b203212e;p=GitHub%2Fmt8127%2Fandroid_kernel_alcatel_ttab.git Btrfs: fix async worker startup race After a new worker thread starts, it is placed into the list of idle threads. But, this may race with a check for idle done by the worker thread itself, resulting in a double list_add operation. This fix adds a check to make sure the idle thread addition is done properly. Signed-off-by: Chris Mason --- diff --git a/fs/btrfs/async-thread.c b/fs/btrfs/async-thread.c index 6ea5cd0a595f..73df627ab8ab 100644 --- a/fs/btrfs/async-thread.c +++ b/fs/btrfs/async-thread.c @@ -74,7 +74,12 @@ static void check_idle_worker(struct btrfs_worker_thread *worker) unsigned long flags; spin_lock_irqsave(&worker->workers->lock, flags); worker->idle = 1; - list_move(&worker->worker_list, &worker->workers->idle_list); + + /* 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); } } @@ -90,8 +95,11 @@ static void check_busy_worker(struct btrfs_worker_thread *worker) unsigned long flags; spin_lock_irqsave(&worker->workers->lock, flags); worker->idle = 0; - list_move_tail(&worker->worker_list, - &worker->workers->worker_list); + + if (!list_empty(&worker->worker_list)) { + list_move_tail(&worker->worker_list, + &worker->workers->worker_list); + } spin_unlock_irqrestore(&worker->workers->lock, flags); } }