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SubjectRe: 3.14.0+/x86: lockdep and mutexes not getting along
On Thu, Apr 10, 2014 at 11:18:24AM +0200, Peter Zijlstra wrote:
> So I managed to reproduce, and the below makes it go away. I just don't
> understand why though. will stare more.

/me kicks himself.. bloody obvious fail there :-)

Not unlocking the lock after a lockdep trigger will make things get
stuck real fast :-)

---
kernel/locking/mutex-debug.c | 19 +++++++++----------
1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
index e1191c996c59..5cf6731b98e9 100644
--- a/kernel/locking/mutex-debug.c
+++ b/kernel/locking/mutex-debug.c
@@ -71,18 +71,17 @@ void mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,

void debug_mutex_unlock(struct mutex *lock)
{
- if (unlikely(!debug_locks))
- return;
+ if (likely(debug_locks)) {
+ DEBUG_LOCKS_WARN_ON(lock->magic != lock);

- DEBUG_LOCKS_WARN_ON(lock->magic != lock);
+ if (!lock->owner)
+ DEBUG_LOCKS_WARN_ON(!lock->owner);
+ else
+ DEBUG_LOCKS_WARN_ON(lock->owner != current);

- if (!lock->owner)
- DEBUG_LOCKS_WARN_ON(!lock->owner);
- else
- DEBUG_LOCKS_WARN_ON(lock->owner != current);
-
- DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next);
- mutex_clear_owner(lock);
+ DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next);
+ mutex_clear_owner(lock);
+ }

/*
* __mutex_slowpath_needs_to_unlock() is explicitly 0 for debug

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