[PATCH] ocfs2: fix lock acquisition order in refcounttree

[Diogo Jahchan Koike <djahchankoike@gmail.com>]

Acquiring the locks in refcounttree should follow
the ip_alloc --> ip_xattr ordering, as done by multiple
code paths in ocfs2; otherwise, we risk an ABBA deadlock
(i.e in the start transaction path).

Reported-by: syzbot+1fed2de07d8e11a3ec1b@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=1fed2de07d8e11a3ec1b
Tested-by: syzbot+1fed2de07d8e11a3ec1b@syzkaller.appspotmail.com
Reviewed-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Diogo Jahchan Koike <djahchankoike@gmail.com>
---
 fs/ocfs2/refcounttree.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/ocfs2/refcounttree.c b/fs/ocfs2/refcounttree.c
index 8f732742b26e..c8467b92b64e 100644
--- a/fs/ocfs2/refcounttree.c
+++ b/fs/ocfs2/refcounttree.c
@@ -928,8 +928,8 @@ int ocfs2_try_remove_refcount_tree(struct inode *inode,
 	struct ocfs2_inode_info *oi = OCFS2_I(inode);
 	struct ocfs2_dinode *di = (struct ocfs2_dinode *)di_bh->b_data;
 
-	down_write(&oi->ip_xattr_sem);
 	down_write(&oi->ip_alloc_sem);
+	down_write(&oi->ip_xattr_sem);
 
 	if (oi->ip_clusters)
 		goto out;
@@ -945,8 +945,8 @@ int ocfs2_try_remove_refcount_tree(struct inode *inode,
 	if (ret)
 		mlog_errno(ret);
 out:
-	up_write(&oi->ip_alloc_sem);
 	up_write(&oi->ip_xattr_sem);
+	up_write(&oi->ip_alloc_sem);
 	return 0;
 }
 
-- 
2.43.0