linux-kernel - Re: 3.5-rc6 futex_wait_requeue

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Message-ID: <alpine.LFD.2.02.1207132108340.32033@ionos>
Date:	Fri, 13 Jul 2012 21:11:57 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dave Jones <davej@...hat.com>
cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Darren Hart <darren@...art.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: 3.5-rc6 futex_wait_requeue_pi oops.

On Fri, 13 Jul 2012, Dave Jones wrote:

> On Fri, Jul 13, 2012 at 08:47:38PM +0200, Thomas Gleixner wrote:
>  > On Fri, 13 Jul 2012, Dave Jones wrote:
>  > 
>  > > Looks like calling futex() with garbage makes things unhappy.
>  > 
>  >                 WARN_ON(!&q.pi_state);
>  >                 pi_mutex = &q.pi_state->pi_mutex;
>  >                 ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
>  >                 debug_rt_mutex_free_waiter(&rt_waiter);
>  > 
>  > So there is some weird way which causes q.pi_state = NULL. Dave, did
>  > you see the warning before the oops happened ?
> 
> No, that didn't seem to trigger.

Yuck. The rt_mutex is embedded in pi_state and not a pointer and the
thing explodes in __lock_acquire if the raw lock protecting the
rtmutex internals. 

Can you decode the exact code line ?

Thanks,

	tglx


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