[PATCH] btrfs: don't double lock the subvol_sem

[PATCH] btrfs: don't double lock the subvol_sem

[Josef Bacik]

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>
---
 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 b13c212b1bed..8db7455fee38 100644
--- 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 @@ static int btrfs_rename_exchange(struct inode *old_dir,
 		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));
-- 
2.23.0

Re: [PATCH] btrfs: don't double lock the subvol_sem

[David Sterba]

On Tue, Nov 19, 2019 at 01:59:20PM -0500, Josef Bacik wrote:
> 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>

Added to misc-next, thanks.