Btrfs: fix worker lock misuse in find_worker

Dan Carpenter noticed that we were doing a double unlock on the worker
lock, and sometimes picking a worker thread without the lock held.

This fixes both errors.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/btrfs/async-thread.c b/fs/btrfs/async-thread.c
index cb97174e2366..0b394580d860 100644
--- a/fs/btrfs/async-thread.c
+++ b/fs/btrfs/async-thread.c
@@ -563,8 +563,8 @@ static struct btrfs_worker_thread *find_worker(struct btrfs_workers *workers)
         struct list_head *fallback;
         int ret;
 
-again:
         spin_lock_irqsave(&workers->lock, flags);
+again:
         worker = next_worker(workers);
 
         if (!worker) {
@@ -579,6 +579,7 @@ again:
                         spin_unlock_irqrestore(&workers->lock, flags);
                         /* we're below the limit, start another worker */
                         ret = __btrfs_start_workers(workers);
+                        spin_lock_irqsave(&workers->lock, flags);
                         if (ret)
                                 goto fallback;
                         goto again;