linux-kernel - Re: sched/cputime: sig->prev

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Message-ID: <20130503110003.GA1588@redhat.com>
Date:	Fri, 3 May 2013 13:00:04 +0200
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	Dave Hansen <dave@...1.net>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Subject: Re: sched/cputime: sig->prev_stime underflow

On Thu, May 02, 2013 at 09:05:28AM -0700, Dave Hansen wrote:
> On 04/30/2013 05:36 AM, Stanislaw Gruszka wrote:
> > On Tue, Apr 16, 2013 at 02:05:22PM -0700, Dave Hansen wrote:
> >>> But since this (most likely) is rtime monotonicity problem it
> >>> is bug by itself and probably that should be fixed. Can you 
> >>> check second patch attached and see if it trigger the warning.
> >>
> >> Yup, it triggers lots of warnings.  Here's one.
> >>
> >>> [  460.789710] ------------[ cut here ]------------
> >>> [  460.789730] WARNING: at /home/davehans/linux.git/kernel/sched/cputime.c:563 cputime_adjust+0xe6/0xf0()
> >>> [  460.789736] Hardware name: PRIMEQUEST 1800E2
> >>> [  460.789739] Modules linked in:
> >>> [  460.789745] Pid: 4245, comm: top Tainted: G        W    3.9.0-rc7-00004-gbb33db7-dirty #19
> >>> [  460.789748] Call Trace:
> >>> [  460.789777]  [<ffffffff810c6dc7>] warn_slowpath_common+0xb7/0x120
> >>> [  460.789783]  [<ffffffff810c6e5a>] warn_slowpath_null+0x2a/0x40
> >>> [  460.789789]  [<ffffffff8111a8d6>] cputime_adjust+0xe6/0xf0
> >>> [  460.789795]  [<ffffffff8111b755>] ? thread_group_cputime+0x5/0x140
> >>> [  460.789800]  [<ffffffff8111bbb9>] thread_group_cputime_adjusted+0x59/0x70
> > 
> > Dave, could you test attached patch and check if make warnings gone.
> > Patch is not right fix, but if it prevent the warnings, this will
> > give clue where the problem can be.
> 
> Does this have any relation to the other four -tip patches you also
> posted?  What do you want this applied on top of?

No, they are not related. But if you apply patch " sched: Avoid
prev->stime underflow", you will also need previous additional
patch, which WARN if rtime goes backward to detect that condition
and see if it is fixed by times->sum_exec_runtime calculation
change.

Stanislaw
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