linux-kernel - Re: task

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Message-ID: <20141123181717.GA13198@redhat.com>
Date:	Sun, 23 Nov 2014 19:17:18 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>, x86-ml <x86@...nel.org>
Subject: Re: task_stat splat

On 11/23, Oleg Nesterov wrote:
>
> On 11/23, Oleg Nesterov wrote:
> >
> > On 11/23, Borislav Petkov wrote:
> > >
> > > where we end up with a zero PMD. RIP is corrupted too so we're somewhere
> > > off in the fields.
> >
> > PMD = 0 is fine I guess, addr == 0 is not mapped.
> >
> > > Comment over thread_group_cputime() talks about dead tasks accounting
> >
> > This comment simply means that we also need to read the accumulated
> > counters in tsk->signal.
> >
> > > which might be relevant as we're seeing not mapped page hierarchy so
> > > something must have gone away recently but we try to look at it.
> >
> > This is called under ->siglock, we can't race with exit/etc. But this
> > doesn't matter, it is not that we (say) get t == NULL or something like
> > this.
> >
> > RIP == 0, and this looks "impossible", I do not see indirect function
> > calls in this paths.
>
> Ah, I didn't notice you mentioned tip/master... so it looks as if
> sched_class->update_curr is NULL?

Perhaps this is migration thread? stop_sched_class doesn't have ->update_curr.

could you try to cat /proc/pid-of-migration-thread/stat on your machine?

Oleg.

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