Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758381Ab3EQWWH (ORCPT ); Fri, 17 May 2013 18:22:07 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:54089 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756899Ab3EQVhR (ORCPT ); Fri, 17 May 2013 17:37:17 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Stanislaw Gruszka , Frederic Weisbecker , Linus Torvalds , Dave Hansen , Peter Zijlstra , Ingo Molnar , rostedt@goodmis.org Subject: [ 023/102] sched: Avoid prev->stime underflow Date: Fri, 17 May 2013 14:35:38 -0700 Message-Id: <20130517213246.830373308@linuxfoundation.org> X-Mailer: git-send-email 1.8.3.rc0.20.gb99dd2e In-Reply-To: <20130517213244.277411019@linuxfoundation.org> References: <20130517213244.277411019@linuxfoundation.org> User-Agent: quilt/0.60-5.1.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2664 Lines: 86 3.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Stanislaw Gruszka commit 68aa8efcd1ab961e4684ef5af32f72a6ec1911de upstream. Dave Hansen reported strange utime/stime values on his system: https://lkml.org/lkml/2013/4/4/435 This happens because prev->stime value is bigger than rtime value. Root of the problem are non-monotonic rtime values (i.e. current rtime is smaller than previous rtime) and that should be debugged and fixed. But since problem did not manifest itself before commit 62188451f0d63add7ad0cd2a1ae269d600c1663d "cputime: Avoid multiplication overflow on utime scaling", it should be threated as regression, which we can easily fixed on cputime_adjust() function. For now, let's apply this fix, but further work is needed to fix root of the problem. Reported-and-tested-by: Dave Hansen Signed-off-by: Stanislaw Gruszka Cc: Frederic Weisbecker Cc: rostedt@goodmis.org Cc: Linus Torvalds Cc: Dave Hansen Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/1367314507-9728-3-git-send-email-sgruszka@redhat.com Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- kernel/sched/cputime.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -574,7 +574,7 @@ static void cputime_adjust(struct task_c struct cputime *prev, cputime_t *ut, cputime_t *st) { - cputime_t rtime, stime, total; + cputime_t rtime, stime, utime, total; stime = curr->stime; total = stime + curr->utime; @@ -599,13 +599,13 @@ static void cputime_adjust(struct task_c if (prev->stime + prev->utime >= rtime) goto out; - if (!rtime) { - stime = 0; - } else if (!total) { - stime = rtime; - } else { + if (total) { stime = scale_stime((__force u64)stime, (__force u64)rtime, (__force u64)total); + utime = rtime - stime; + } else { + stime = rtime; + utime = 0; } /* @@ -614,7 +614,7 @@ static void cputime_adjust(struct task_c * Let's enforce monotonicity. */ prev->stime = max(prev->stime, stime); - prev->utime = max(prev->utime, rtime - prev->stime); + prev->utime = max(prev->utime, utime); out: *ut = prev->utime; -- 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/