On Wed, Jun 04, 2014 at 09:53:16PM +0200, Thomas Gleixner wrote:
> 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.
Ah. Yeah. I haven't tested this but it seems sane to me.
>
> 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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