Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751709AbbLKNZ5 (ORCPT ); Fri, 11 Dec 2015 08:25:57 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:47443 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750908AbbLKNZ4 (ORCPT ); Fri, 11 Dec 2015 08:25:56 -0500 Date: Fri, 11 Dec 2015 14:25:51 +0100 From: Peter Zijlstra To: Andrey Ryabinin Cc: mingo@redhat.com, linux-kernel@vger.kernel.org, yuyang.du@intel.com, Morten Rasmussen , Paul Turner , Ben Segall Subject: Re: [PATCH] sched/fair: fix mul overflow on 32-bit systems Message-ID: <20151211132551.GO6356@twins.programming.kicks-ass.net> References: <1449838518-26543-1-git-send-email-aryabinin@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1449838518-26543-1-git-send-email-aryabinin@virtuozzo.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1814 Lines: 44 On Fri, Dec 11, 2015 at 03:55:18PM +0300, Andrey Ryabinin wrote: > Make 'r' 64-bit type to avoid overflow in 'r * LOAD_AVG_MAX' > on 32-bit systems: > UBSAN: Undefined behaviour in kernel/sched/fair.c:2785:18 > signed integer overflow: > 87950 * 47742 cannot be represented in type 'int' > > Fixes: 9d89c257dfb9 ("sched/fair: Rewrite runnable load and utilization average tracking") > Signed-off-by: Andrey Ryabinin > --- > kernel/sched/fair.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index e3266eb..733f0b8 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -2780,14 +2780,14 @@ static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) > int decayed, removed = 0; > > if (atomic_long_read(&cfs_rq->removed_load_avg)) { > - long r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0); > + s64 r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0); > sa->load_avg = max_t(long, sa->load_avg - r, 0); > sa->load_sum = max_t(s64, sa->load_sum - r * LOAD_AVG_MAX, 0); This makes sense, because sched_avg::load_sum is u64. > removed = 1; > } > > if (atomic_long_read(&cfs_rq->removed_util_avg)) { > - long r = atomic_long_xchg(&cfs_rq->removed_util_avg, 0); > + s64 r = atomic_long_xchg(&cfs_rq->removed_util_avg, 0); > sa->util_avg = max_t(long, sa->util_avg - r, 0); > sa->util_sum = max_t(s32, sa->util_sum - r * LOAD_AVG_MAX, 0); > } However sched_avg::util_sum is u32, so this is still wrecked. -- 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/