linux-kernel - Re: [RFC][PATCH] muptiple bugs in PI futexes

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Date:	Tue, 5 Jun 2007 21:39:49 +0400
From:	Alexey Kuznetsov <kuznet@....inr.ac.ru>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ulrich Drepper <drepper@...hat.com>
Subject: Re: [RFC][PATCH] muptiple bugs in PI futexes

Hello!

> Hmm, what means not expected ? -ESRCH is returned, when the owner task
> is not found. 

This is not supposed to happen with robust futexes.

glibs aborts (which is correct), or for build with disabled debugging
enters simulated deadlock (which is confusing).

> lock. Also using uval is wrong.

Yup. You are right.

This means those RETRY messages could be spurious. I must rerun the test.

> This does not really explain, why you do prevent the -ESRCH return value
> in the next cycle,

Because right curval is refetched, it already has FUTEX_OWNER_DIED bit set
and we succesfully take the lock.

> No, -EDEADLK is returned from here:
> 
> 	ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);

Of course. It is the only place where ret is set. :-)

> 
> The rtmutex code only returns -EDEADLK, when the lock is already held by
> the task

This case.

> The fix is to remove it and to find the real cause of the problem.
> 
> I'm running the glibc tests since hours w/o tripping into it.

OK.

You need run only tst-robustpi8 in loop. It should be triggered quickly,
a few of minutes on 8-way smp here.

If you want, I can insert some debugging printks, which you need,
and run the test here.

Alexey
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