Re: [TIP][RFC 6/7] futex: add requeue_pi calls

[Darren Hart]

Thomas Gleixner wrote:
> On Thu, 5 Mar 2009, Darren Hart wrote:
> > int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
> > 			      struct rt_mutex_waiter *waiter,
> > 			      struct task_struct *task, int detect_deadlock)
> > {
> > 	int ret;
> >
> > 	spin_lock(&lock->wait_lock);
> > 	ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
> >
> >
> > I add the following line to fix the bug.  Question is, should I use this
> > atomic
> > optimization here (under the lock->wait_lock) or should I just do "lock->owner
> > |= RT_MUTEX_HAS_WAITERS" ?
> >
> > =====>	mark_rt_mutex_waiters(lock);
>
> This is still not enough as I explained in the review of the original
> patch. What you need to do is:
>
> 	if (try_to_take_rt_mutex(lock, task)) {
> 	   	spin_unlock(&lock->wait_lock);
> 		/* The caller needs to wake up task, as it is now the owner */
> 		return WAKEIT;
> 	}
>
> 	ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);

Right, so I'm testing this out:

	mark_rt_mutex_waiters(lock);

	if (!rt_mutex_owner(lock) || try_to_steal_lock(lock, task)) {
		/* We got the lock for task. */
		debug_rt_mutex_lock(lock);

		rt_mutex_set_owner(lock, task, 0);

		rt_mutex_deadlock_account_lock(lock, task);
		return 1;
	}

Steven, is this the proper use of the debug* routines?  I copied them 
from try_to_take_rt_mutex(), but they are empty routines without 
comments so I wasn't sure exactly how they were intended to be used. 
Does the usage of debug_rt_mutex_lock() assume task=current (the other 
has the task_struct passed int).

Thanks,

Darren


> > 	if (ret && !waiter->task) {
> > 		/*
> > 		 * Reset the return value. We might have
> > 		 * returned with -EDEADLK and the owner
> > 		 * released the lock while we were walking the
> > 		 * pi chain.  Let the waiter sort it out.
> > 		 */
> > 		ret = 0;
> > 	}
> > 	spin_unlock(&lock->wait_lock);
> >
> > 	debug_rt_mutex_print_deadlock(waiter);
> >
> > 	return ret;
> > }
>
> Thanks,
>
> 	tglx


--
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
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