Re: 3.5-rc6 futex_wait_requeue_pi oops.

From: Thomas Gleixner
Date: Fri Jul 13 2012 - 15:11:56 EST


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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