linux-kernel - Re: task

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Date:	Sun, 23 Nov 2014 18:56:41 +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, 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?

>
> > [42460.389625] Call Trace:
> > [42460.389635]  [<ffffffff810813d9>] ? task_sched_runtime+0x99/0xc0
> > [42460.389643]  [<ffffffff81088b5c>] thread_group_cputime+0x17c/0x2d0
>
> Could you identify somehow the line which matches task_sched_runtime+0x99 ?
> Probably do_task_delta_exec()...
>
> Oleg.

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