linux-kernel - Re: lockdep: Warning & NULL ptr deref

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Date:	Tue, 28 Feb 2012 15:20:53 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Dave Jones <davej@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: lockdep: Warning & NULL ptr deref

On Tue, 2012-02-28 at 16:19 +0200, Sasha Levin wrote:
> On Tue, Feb 28, 2012 at 3:29 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Tue, 2012-02-28 at 10:24 -0500, Sasha Levin wrote:
> >>
> >> I'll send some patches to prevent the NULL deref itself which happens
> >> since a chunk of the code in lockdep.c assumed hlock_class() can't
> >> return NULL.
> >>
> > There's tons of code actually assuming that..
> >
> >> This won't fix the actual problem though, I'm not sure exactly how a
> >> held lock wouldn't have a class initialized to it.
> >
> > static inline struct lock_class *hlock_class(struct held_lock *hlock)
> > {
> >        if (!hlock->class_idx) {
> >                /*
> >                 * Someone passed in garbage, we give up.
> >                 */
> >                DEBUG_LOCKS_WARN_ON(1);
> >                return NULL;
> >        }
> >        return lock_classes + hlock->class_idx - 1;
> > }
> >
> > Typically that translates to severe memory corruption.
> 
> I can also reproduce it easily by triggering sysrq once or twice after
> trinity has stopped.

What's trinity ?
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