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 <chris.mason@oracle.com>
diff --git a/fs/btrfs/async-thread.c b/fs/btrfs/async-thread.c
index 6ea5cd0..73df627 100644
--- a/fs/btrfs/async-thread.c
+++ b/fs/btrfs/async-thread.c
@@ -74,7 +74,12 @@
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 @@
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);
}
}