linux-kernel - Re: [PATCH -tip] sched/cputime: do not scale when utime == 0

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Message-ID: <20130904123350.GA9773@gmail.com>
Date:	Wed, 4 Sep 2013 14:33:50 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Stanislaw Gruszka <sgruszka@...hat.com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -tip] sched/cputime: do not scale when utime == 0


* Stanislaw Gruszka <sgruszka@...hat.com> wrote:

> scale_stime() silently assumes that stime < rtime, otherwise when
> stime == rtime and both values are big (operations on them do not fit
> in 32 bits), the resulting scaling stime can be bigger than rtime.
> In consequence utime = rtime - stime results in negative value.

Please also describe observed/expected symptoms of this bug in apps, so 
that we can later on redirect bugreporters to this fix and filter out new 
symptoms (if any).

Thanks,

	Ingo
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