Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751169AbaAENGV (ORCPT ); Sun, 5 Jan 2014 08:06:21 -0500 Received: from mail-wg0-f50.google.com ([74.125.82.50]:48840 "EHLO mail-wg0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751050AbaAENGT (ORCPT ); Sun, 5 Jan 2014 08:06:19 -0500 Date: Sun, 5 Jan 2014 14:06:16 +0100 From: Frederic Weisbecker To: Kevin Hilman Cc: Thomas Gleixner , linux-kernel@vger.kernel.org, linaro-kernel@lists.linaro.org, Peter Zijlstra , Ingo Molnar Subject: Re: [PATCH 2/2] sched/nohz: fix overflow error in scheduler_tick_max_deferment() Message-ID: <20140105130612.GB17617@localhost.localdomain> References: <1387315388-31676-1-git-send-email-khilman@linaro.org> <1387315388-31676-2-git-send-email-khilman@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1387315388-31676-2-git-send-email-khilman@linaro.org> 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 On Tue, Dec 17, 2013 at 01:23:08PM -0800, Kevin Hilman wrote: > The conversion of the max deferment from usecs to nsecs can easily > overflow on platforms where a long is 32-bits. To fix, cast the usecs > value to u64 before multiplying by NSECS_PER_USEC. > > This was discovered on 32-bit ARM platform when extending the max > deferment value. > > Cc: Frederic Weisbecker > Signed-off-by: Kevin Hilman > --- > kernel/sched/core.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 4b1fe3e69fe4..3d7c80e1c4d9 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2203,7 +2203,7 @@ u64 scheduler_tick_max_deferment(void) > if (time_before_eq(next, now)) > return 0; > > - return jiffies_to_usecs(next - now) * NSEC_PER_USEC; > + return (u64)jiffies_to_usecs(next - now) * NSEC_PER_USEC; Just to be sure I understand the issue. The problem is that jiffies_to_usecs() return an unsigned int which is then multiplied by NSEC_PER_USEC. If the result of the mul is too big to be stored in an unsigned int, we overflow and may loose some high part of the result. Right? > } > > static __init int sched_nohz_full_init_debug(void) > -- > 1.8.3 > -- 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/