From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753432AbcHALuh (ORCPT ); Mon, 1 Aug 2016 07:50:37 -0400 Received: from foss.arm.com ([217.140.101.70]:33413 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752179AbcHALu3 (ORCPT ); Mon, 1 Aug 2016 07:50:29 -0400 Date: Mon, 1 Aug 2016 12:43:55 +0100 From: Juri Lelli To: Tommaso Cucinotta Cc: Luca Abeni , Juri Lelli , Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, linux-dl@retis.sssup.it Subject: Re: [RFC PATCH 1/4] Minimally invasive deadline wrap-around bugfix for SCHED_DEADLINE cpu heap Message-ID: <20160801114355.GT22472@e106622-lin> References: <1468921493-10054-1-git-send-email-tommaso.cucinotta@sssup.it> <1468921493-10054-2-git-send-email-tommaso.cucinotta@sssup.it> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1468921493-10054-2-git-send-email-tommaso.cucinotta@sssup.it> 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 Hi, On 19/07/16 11:44, Tommaso Cucinotta wrote: > Current code in cpudeadline.c has a bug in re-heapifying when adding a > new element at the end of the heap, because a deadline value of 0 is > temporarily set in the new elem, then cpudl_change_key() is called > with the actual elem deadline as param. However, the function compares > the new deadline to set with the one previously in the elem, which is > 0. So, if current absolute deadlines grew so much to have negative > values as s64, the comparison in cpudl_change_key() makes the wrong > decision. Instead, as from dl_time_before(), the kernel should handle > correctly abs deadlines wrap-arounds. > > This patch fixes the problem with a minimally invasive change that > forces cpudl_change_key() to heapify up in this case. > > Cc: Peter Zijlstra > Cc: Juri Lelli > Cc: Luca Abeni > Reviewed-by: Luca Abeni > Signed-off-by: Tommaso Cucinotta > --- > kernel/sched/cpudeadline.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c > index 5be5882..d418449 100644 > --- a/kernel/sched/cpudeadline.c > +++ b/kernel/sched/cpudeadline.c > @@ -168,7 +168,7 @@ void cpudl_set(struct cpudl *cp, int cpu, u64 dl, int is_valid) > > if (old_idx == IDX_INVALID) { > cp->size++; > - cp->elements[cp->size - 1].dl = 0; > + cp->elements[cp->size - 1].dl = dl; > cp->elements[cp->size - 1].cpu = cpu; > cp->elements[cpu].idx = cp->size - 1; > cpudl_change_key(cp, cp->size - 1, dl); Looks good. I'd only change the subject to something like: sched/deadline: Wrap-around bugfix for cpu heap Best, - Juri