ceph_wait_on_conflict_unlink(): grab reference before dropping ->d_lock

[ Upstream commit dc32464 ]

Use of dget() after we'd dropped ->d_lock is too late - dentry might
be gone by that point.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Al Viro

fs/ceph/mds_client.c

@@ -709,8 +709,8 @@ int ceph_wait_on_conflict_unlink(struct dentry *dentry)
 		if (!d_same_name(udentry, pdentry, &dname))
 			goto next;
 
+		found = dget_dlock(udentry);
 		spin_unlock(&udentry->d_lock);
-		found = dget(udentry);
 		break;
 next:
 		spin_unlock(&udentry->d_lock);