[PATCH 4.19 014/219] btrfs: dont double lock the subvol_sem for rename exchange

Greg Kroah-Hartman
2019-12-29T17:28:07Z

From: Josef Bacik <josef@toxicpanda.com>

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>

---
fs/btrfs/inode.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)

--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9491,9 +9491,8 @@ static int btrfs_rename_exchange(struct
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);

/*
@@ -9727,9 +9726,8 @@ 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));