Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754847AbYJHNBe (ORCPT ); Wed, 8 Oct 2008 09:01:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755546AbYJHNBR (ORCPT ); Wed, 8 Oct 2008 09:01:17 -0400 Received: from e32.co.us.ibm.com ([32.97.110.150]:50552 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754632AbYJHNBP (ORCPT ); Wed, 8 Oct 2008 09:01:15 -0400 Subject: [PATCH] sched_clock: prevent scd->clock from moving backwards From: Dave Kleikamp To: Jeremy Fitzhardinge Cc: Peter Zijlstra , Steven Rostedt , Ingo Molnar , Linux Kernel Mailing List In-Reply-To: <1223470773.6336.13.camel@norville.austin.ibm.com> References: <48D959E8.4000303@goop.org> <1223470773.6336.13.camel@norville.austin.ibm.com> Content-Type: text/plain Date: Wed, 08 Oct 2008 08:00:54 -0500 Message-Id: <1223470854.6336.15.camel@norville.austin.ibm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1563 Lines: 42 sched_clock: prevent scd->clock from moving backwards When sched_clock_cpu() couples the clocks between two cpus, it may increment scd->clock beyond the GTOD tick window that __update_sched_clock() uses to clamp the clock. A later call to __update_sched_clock() may move the clock back to scd->tick_gtod + TICK_NSEC, violating the clock's monotonic property. This patch ensures that scd->clock will not be set backward. Signed-off-by: Dave Kleikamp Cc: Ingo Molnar Cc: Peter Zijlstra diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c index e8ab096..a989d64 100644 --- a/kernel/sched_clock.c +++ b/kernel/sched_clock.c @@ -118,13 +118,13 @@ static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now) /* * scd->clock = clamp(scd->tick_gtod + delta, - * max(scd->tick_gtod, scd->clock), - * scd->tick_gtod + TICK_NSEC); + * max(scd->tick_gtod, scd->clock), + * min(scd->clock, scd->tick_gtod + TICK_NSEC)); */ clock = scd->tick_gtod + delta; min_clock = wrap_max(scd->tick_gtod, scd->clock); - max_clock = scd->tick_gtod + TICK_NSEC; + max_clock = wrap_min(scd->clock, scd->tick_gtod + TICK_NSEC); clock = wrap_max(clock, min_clock); clock = wrap_min(clock, max_clock); -- 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/