linux-kernel - Re: [PATCH v2] sched: fix user time incorrectly accounted as system time on 32 bit

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Date:	Tue, 14 Sep 2010 16:37:28 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stanislaw Gruszka <sgruszka@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	stable@...nel.org,
	Michael Chapman <redhat-bugzilla@...y.puzzling.org>,
	Ciriaco Garcia de Celis <sysman@...erpilot.com>
Subject: Re: [PATCH v2] sched: fix user time incorrectly accounted as
 system time on 32 bit

On Tue, 2010-09-14 at 16:35 +0200, Stanislaw Gruszka wrote:
> We have 32 bit variable overflow possibility when multiply in
> task_times() and thread_group_times() functions. If overflow happens
> calculated scaled utime value become wrongly small and scaled stime
> wrongly big.

Ah, right, (u64)foo * bar would have worked too I guess, but yeah, the
used (u64)(foo * bar) is wrong.

> Reported here:
> https://bugzilla.redhat.com/show_bug.cgi?id=633037
> https://bugzilla.kernel.org/show_bug.cgi?id=16559
> 
> Reported-by: Michael Chapman <redhat-bugzilla@...y.puzzling.org>
> Reported-by: Ciriaco Garcia de Celis <sysman@...erpilot.com>
> Cc: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: <stable@...nel.org>  # 2.6.32.19+ (partially) and 2.6.33+
> Signed-off-by: Stanislaw Gruszka <sgruszka@...hat.com>

Thanks, got it.
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