[PATCH 4.9 088/171] btrfs: dont double lock the subvol_sem for rename exchange

Greg Kroah-Hartman
2020-01-02T22:30:26Z

From: Josef Bacik <josef@toxicpanda.com>

[ Upstream commit 943eb3bf25f4a7b745dd799e031be276aa104d82 ]

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: Sasha Levin <sashal@kernel.org>
---
fs/btrfs/inode.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 80937c5ca477..bb8863958ac0 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9597,9 +9597,8 @@ static int btrfs_rename_exchange(struct inode *old_dir,
return -EXDEV;

/* close the race window with snapshot create/destroy ioctl */
- if (old_ino == BTRFS_FIRST_FREE_OBJECTID)
- down_read(&root->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(&dest->fs_info->subvol_sem);

/*
@@ -9785,9 +9784,8 @@ static int btrfs_rename_exchange(struct inode *old_dir,
ret2 = btrfs_end_transaction(trans, root);
ret = ret ? ret : ret2;
out_notrans:
- if (new_ino == BTRFS_FIRST_FREE_OBJECTID)
- up_read(&dest->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(&root->fs_info->subvol_sem);

return ret;
--
2.20.1