[PATCH v2] Btrfs, lockdep: get_restripe_target: use lockdep in BUG_ON

[Bobby Powers <bobbypowers@gmail.com>]

spin_is_locked always returns 0 on non-SMP systems, which causes btrfs
to fail the mount.  There is documentation pending as to why checking
for spin_is_locked is a bad idea:

https://lkml.org/lkml/2012/3/27/413

The suggested lockdep_assert_held() is not appropriate in this case,
as what get_restripe_target() is checking for is that either
volume_mutex is held or balance_lock is held.  Luckily
lockdep_assert_held() is a simple macro:

WARN_ON(debug_locks && !lockdep_is_held(l))

We can mimic the structure in get_restripe_target(), but we need to
make sure lockdep_is_held() is defined for the !LOCKDEP case.

CC: Ilya Dryomov <idryomov@gmail.com>
CC: Chris Mason <chris.mason@oracle.com>
CC: Andi Kleen <ak@linux.intel.com>
CC: Jeff Mahoney <jeffm@suse.de>
CC: Ingo Molnar <mingo@redhat.com>
CC: linux-kernel@vger.kernel.org
Signed-off-by: Bobby Powers <bobbypowers@gmail.com>
---
 fs/btrfs/extent-tree.c  |    5 +++--
 include/linux/lockdep.h |    1 +
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index a844204..4d13eb1 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -24,6 +24,7 @@
 #include <linux/kthread.h>
 #include <linux/slab.h>
 #include <linux/ratelimit.h>
+#include <linux/lockdep.h>
 #include "compat.h"
 #include "hash.h"
 #include "ctree.h"
@@ -3158,8 +3159,8 @@ static u64 get_restripe_target(struct btrfs_fs_info *fs_info, u64 flags)
 	struct btrfs_balance_control *bctl = fs_info->balance_ctl;
 	u64 target = 0;
 
-	BUG_ON(!mutex_is_locked(&fs_info->volume_mutex) &&
-	       !spin_is_locked(&fs_info->balance_lock));
+	BUG_ON(debug_locks && !lockdep_is_held(&fs_info->volume_mutex) &&
+	       !lockdep_is_held(&fs_info->balance_lock));
 
 	if (!bctl)
 		return 0;
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index d36619e..94c0edb 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -392,6 +392,7 @@ struct lock_class_key { };
 
 #define lockdep_depth(tsk)	(0)
 
+#define lockdep_is_held(l)	(0)
 #define lockdep_assert_held(l)			do { } while (0)
 
 #define lockdep_recursing(tsk)			(0)
-- 
1.7.10.rc3.3.g19a6c