From: Josef Bacik <josef@toxicpanda.com>
Date: Tue, 19 Nov 2019 13:59:20 -0500
Subject: btrfs: don't double lock the subvol_sem for rename exchange
Git-commit: 943eb3bf25f4a7b745dd799e031be276aa104d82
Patch-mainline: v5.5-rc3
References: bsc#1162943

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>
Acked-by: Nikolay Borisov <nborisov@suse.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 5766c2d19896..e3c76645cad7 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9554,9 +9554,8 @@ 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);

 	/*
@@ -9790,9 +9789,8 @@ 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));