[PATCH 4.9 085/120] btrfs: fix locking when we put back a delayed ref thats too new

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jeff Mahoney <jeffm@xxxxxxxx>

commit d0280996437081dd12ed1e982ac8aeaa62835ec4 upstream.

In __btrfs_run_delayed_refs, when we put back a delayed ref that's too
new, we have already dropped the lock on locked_ref when we set
->processing = 0.

This patch keeps the lock to cover that assignment.

Fixes: d7df2c796d7 (Btrfs: attach delayed ref updates to delayed ref heads)
Signed-off-by: Jeff Mahoney <jeffm@xxxxxxxx>
Reviewed-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/btrfs/extent-tree.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2537,11 +2537,11 @@ static noinline int __btrfs_run_delayed_
 		if (ref && ref->seq &&
 		    btrfs_check_delayed_seq(fs_info, delayed_refs, ref->seq)) {
 			spin_unlock(&locked_ref->lock);
-			btrfs_delayed_ref_unlock(locked_ref);
 			spin_lock(&delayed_refs->lock);
 			locked_ref->processing = 0;
 			delayed_refs->num_heads_ready++;
 			spin_unlock(&delayed_refs->lock);
+			btrfs_delayed_ref_unlock(locked_ref);
 			locked_ref = NULL;
 			cond_resched();
 			count++;