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

commit 943eb3bf25f4a7b745dd799e031be276aa104d82 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 10a01dd..10718f9 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9535,9 +9535,8 @@ 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);
 
        /*
@@ -9771,9 +9770,8 @@ 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));