Btrfs: fix race between allocate and release extent buffer.

Increase extent buffer's reference count while holding the lock.
Otherwise it can race with try_release_extent_buffer.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 1 insertions, 2 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 96577e8bf9f..b177ed31961 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3165,10 +3165,9 @@ struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
                 spin_unlock(&tree->buffer_lock);
                 goto free_eb;
         }
-        spin_unlock(&tree->buffer_lock);
-
         /* add one reference for the tree */
         atomic_inc(&eb->refs);
+        spin_unlock(&tree->buffer_lock);
         return eb;
 
 free_eb: