From 166f66d0bc94a14ec4bc6ee6ab079532df4a8d9e Mon Sep 17 00:00:00 2001
From: Zhaolei <zhaolei@cn.fujitsu.com>
Date: Thu, 6 Aug 2015 22:39:36 +0800
Subject: [PATCH] btrfs: Add WARN_ON() for double lock in btrfs_tree_lock()

When a task trying to double lock a extent buffer, there are no
lockdep warning about it because this lock may be in "blocking_lock"
state, and make us hard to debug.

This patch add a WARN_ON() for above condition, it can not report
all deadlock cases(as lock between tasks), but at least helps us
some.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>
---
Reading git-format-patch failed