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

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Date:	Fri, 5 Apr 2013 01:41:29 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Dave Hansen <dave@...1.net>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Stanislaw Gruszka <sgruszka@...hat.com>
Subject: Re: sched/cputime: sig->prev_stime underflow

2013/4/4 Dave Hansen <dave@...1.net>:
> With the 3.9-rcs (and probably much earlier) I'm seeing some weird top
> output where the cpu time "spent" is millions of hours:
>
> 445 root      20   0     0    0    0 S    0  0.0  5124095h kworker/45:1
> 404 root      20   0     0    0    0 S    0  0.0  5124095h kworker/4:1
>
> I see it mostly with kernel threads, but it doesn't seem to happen on my
> distro kernel (3.5 era).  The suspect code is in thread_group_times():
>
>         sig->prev_stime = max(sig->prev_stime, rtime - sig->prev_utime);
>
> In my case, I caught it with rtime=34 and sig->prev_utime=35.  This code
> _looks_ to be pretty mature, coming in at commit 0cf55e1e in 2009.  The
> system I'm running on _does_ have some non-sync'd TSCs, but they are at
> least being detected, so I expect the fallout to be minimal:
>
>         tsc: Marking TSC unstable due to check_tsc_sync_source failed
>
> config:
>
>         http://sr71.net/~dave/linux/config-bigbox-04042013.txt
>
> The dumb fix here would seem to be to just check "rtime <
> sig->prev_utime".  Any thoughts?

Hi Dave,

Does this patch fix the issue for you?
https://lkml.org/lkml/2013/4/4/112
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