btrfs: don't double lock the subvol_sem for rename exchange

If we're rename exchanging two subvols we'll try to lock this lock
twice, which is bad.  Just lock once if either of the ino's are subvols.

Fixes: cdd1fedf8261 ("btrfs: add support for RENAME_EXCHANGE and RENAME_WHITEOUT")
CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 5766c2d..e3c7664 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9554,9 +9554,8 @@ static int btrfs_rename_exchange(struct inode *old_dir,
        btrfs_init_log_ctx(&ctx_dest, new_inode);
 
        /* close the race window with snapshot create/destroy ioctl */
-       if (old_ino == BTRFS_FIRST_FREE_OBJECTID)
-               down_read(&fs_info->subvol_sem);
-       if (new_ino == BTRFS_FIRST_FREE_OBJECTID)
+       if (old_ino == BTRFS_FIRST_FREE_OBJECTID ||
+           new_ino == BTRFS_FIRST_FREE_OBJECTID)
                down_read(&fs_info->subvol_sem);
 
        /*
@@ -9790,9 +9789,8 @@ out_fail:
                ret = ret ? ret : ret2;
        }
 out_notrans:
-       if (new_ino == BTRFS_FIRST_FREE_OBJECTID)
-               up_read(&fs_info->subvol_sem);
-       if (old_ino == BTRFS_FIRST_FREE_OBJECTID)
+       if (new_ino == BTRFS_FIRST_FREE_OBJECTID ||
+           old_ino == BTRFS_FIRST_FREE_OBJECTID)
                up_read(&fs_info->subvol_sem);
 
        ASSERT(list_empty(&ctx_root.list));