On Wed, 4 Jun 2014, Brad Mouring wrote:
> On Wed, Jun 04, 2014 at 08:02:16PM +0200, Thomas Gleixner wrote:
> > I'll fixup the check so it wont break the real deadlock case and queue
> > it.
>
> How would the change break the real deadlock case?
> > /* Deadlock detection */
> > if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
> > + /*
> > + * If the prio chain has changed out from under us, set the task
> > + * to the current owner of the lock in the current waiter and
> > + * continue walking the prio chain
> > + */
> > + if (rt_mutex_owner(lock) && rt_mutex_owner(lock) != task) {
No, sorry. That's wrong.
Your change wreckages the rt_mutex_owner(lock) == top_task test
simply because in that case:
(rt_mutex_owner(lock) && rt_mutex_owner(lock) != task)
evaluates to true.
So we want this:
Index: tip/kernel/locking/rtmutex.c
===================================================================
--- tip.orig/kernel/locking/rtmutex.c
+++ tip/kernel/locking/rtmutex.c
@@ -375,6 +375,26 @@ static int rt_mutex_adjust_prio_chain(st
* walk, we detected a deadlock.
*/
if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
+ /*
+ * If the prio chain has changed out from under us, set the task
+ * to the current owner of the lock in the current waiter and
+ * continue walking the prio chain
+ */
+ if (rt_mutex_owner(lock) && rt_mutex_owner(lock) != task &&
+ rt_mutex_owner(lock) != top_task) {
+ /* Release the old owner */
+ raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+ put_task_struct(task);
+
+ /* Move to the new owner */
+ task = rt_mutex_owner(lock);
+ get_task_struct(task);
+
+ /* Let's try this again */
+ raw_spin_unlock(&lock->wait_lock);
+ goto retry;
+ }
+
debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
raw_spin_unlock(&lock->wait_lock);
ret = deadlock_detect ? -EDEADLK : 0;
--
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