Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763000Ab3IDPfP (ORCPT ); Wed, 4 Sep 2013 11:35:15 -0400 Received: from mail-wg0-f44.google.com ([74.125.82.44]:38077 "EHLO mail-wg0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762986Ab3IDPfN (ORCPT ); Wed, 4 Sep 2013 11:35:13 -0400 Date: Wed, 4 Sep 2013 17:35:08 +0200 From: Frederic Weisbecker To: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, peterz@infradead.org, sergey.senozhatsky@gmail.com, bp@alien8.de, paulmck@linux.vnet.ibm.com, tglx@linutronix.de, sgruszka@redhat.com Cc: linux-tip-commits@vger.kernel.org Subject: Re: [tip:timers/urgent] sched/cputime: Do not scale when utime == 0 Message-ID: <20130904153507.GC2308@somewhere> References: <20130904131602.GC2564@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2202 Lines: 49 On Wed, Sep 04, 2013 at 07:37:22AM -0700, tip-bot for Stanislaw Gruszka wrote: > Commit-ID: 5a8e01f8fa51f5cbce8f37acc050eb2319d12956 > Gitweb: http://git.kernel.org/tip/5a8e01f8fa51f5cbce8f37acc050eb2319d12956 > Author: Stanislaw Gruszka > AuthorDate: Wed, 4 Sep 2013 15:16:03 +0200 > Committer: Ingo Molnar > CommitDate: Wed, 4 Sep 2013 16:31:25 +0200 > > sched/cputime: Do not scale when utime == 0 > > scale_stime() silently assumes that stime < rtime, otherwise > when stime == rtime and both values are big enough (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. > > User space visible symptoms of the bug are overflowed TIME > values on ps/top, for example: > > $ ps aux | grep rcu > root 8 0.0 0.0 0 0 ? S 12:42 0:00 [rcuc/0] > root 9 0.0 0.0 0 0 ? S 12:42 0:00 [rcub/0] > root 10 62422329 0.0 0 0 ? R 12:42 21114581:37 [rcu_preempt] > root 11 0.1 0.0 0 0 ? S 12:42 0:02 [rcuop/0] > root 12 62422329 0.0 0 0 ? S 12:42 21114581:35 [rcuop/1] > root 10 62422329 0.0 0 0 ? R 12:42 21114581:37 [rcu_preempt] > > or overflowed utime values read directly from /proc/$PID/stat > > Reference: > > https://lkml.org/lkml/2013/8/20/259 > > Reported-and-tested-by: Sergey Senozhatsky > Signed-off-by: Stanislaw Gruszka > Cc: stable@vger.kernel.org > Cc: Frederic Weisbecker > Cc: Peter Zijlstra > Cc: Paul E. McKenney > Cc: Borislav Petkov > Link: http://lkml.kernel.org/r/20130904131602.GC2564@redhat.com > Signed-off-by: Ingo Molnar Thanks a lot guys! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/