btrfs: don't double lock the subvol_sem

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.

cc: stable@vger.kernel.org
Fixes: cdd1fedf8261 ("btrfs: add support for RENAME_EXCHANGE and RENAME_WHITEOUT")
Signed-off-by: Josef Bacik <josef@toxicpanda.com>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index b13c212b1bed95dcdb187e212de6fadf8e133275..8db7455fee38adaa1ce59a40c16e4471e184f23b 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9563,9 +9563,8 @@ 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);
 
        /*
@@ -9799,9 +9798,8 @@ 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));