Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755329AbaJ1LDf (ORCPT ); Tue, 28 Oct 2014 07:03:35 -0400 Received: from terminus.zytor.com ([198.137.202.10]:50920 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755288AbaJ1LDa (ORCPT ); Tue, 28 Oct 2014 07:03:30 -0400 Date: Tue, 28 Oct 2014 04:02:38 -0700 From: tip-bot for Yasuaki Ishimatsu Message-ID: Cc: peterz@infradead.org, hpa@zytor.com, torvalds@linux-foundation.org, tglx@linutronix.de, linux-kernel@vger.kernel.org, isimatu.yasuaki@jp.fujitsu.com, mingo@kernel.org Reply-To: mingo@kernel.org, isimatu.yasuaki@jp.fujitsu.com, tglx@linutronix.de, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, hpa@zytor.com, peterz@infradead.org In-Reply-To: <54475703.8000505@jp.fujitsu.com> References: <54475703.8000505@jp.fujitsu.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] sched/fair: Care divide error in update_task_scan_period() Git-Commit-ID: 2847c90e1b3ae95379af24894fc4f98e7f2fd705 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 2847c90e1b3ae95379af24894fc4f98e7f2fd705 Gitweb: http://git.kernel.org/tip/2847c90e1b3ae95379af24894fc4f98e7f2fd705 Author: Yasuaki Ishimatsu AuthorDate: Wed, 22 Oct 2014 16:04:35 +0900 Committer: Ingo Molnar CommitDate: Tue, 28 Oct 2014 10:46:03 +0100 sched/fair: Care divide error in update_task_scan_period() While offling node by hot removing memory, the following divide error occurs: divide error: 0000 [#1] SMP [...] Call Trace: [...] handle_mm_fault [...] ? try_to_wake_up [...] ? wake_up_state [...] __do_page_fault [...] ? do_futex [...] ? put_prev_entity [...] ? __switch_to [...] do_page_fault [...] page_fault [...] RIP [] task_numa_fault RSP The issue occurs as follows: 1. When page fault occurs and page is allocated from node 1, task_struct->numa_faults_buffer_memory[] of node 1 is incremented and p->numa_faults_locality[] is also incremented as follows: o numa_faults_buffer_memory[] o numa_faults_locality[] NR_NUMA_HINT_FAULT_TYPES | 0 | 1 | ---------------------------------- ---------------------- node 0 | 0 | 0 | remote | 0 | node 1 | 0 | 1 | locale | 1 | ---------------------------------- ---------------------- 2. node 1 is offlined by hot removing memory. 3. When page fault occurs, fault_types[] is calculated by using p->numa_faults_buffer_memory[] of all online nodes in task_numa_placement(). But node 1 was offline by step 2. So the fault_types[] is calculated by using only p->numa_faults_buffer_memory[] of node 0. So both of fault_types[] are set to 0. 4. The values(0) of fault_types[] pass to update_task_scan_period(). 5. numa_faults_locality[1] is set to 1. So the following division is calculated. static void update_task_scan_period(struct task_struct *p, unsigned long shared, unsigned long private){ ... ratio = DIV_ROUND_UP(private * NUMA_PERIOD_SLOTS, (private + shared)); } 6. But both of private and shared are set to 0. So divide error occurs here. The divide error is rare case because the trigger is node offline. This patch always increments denominator for avoiding divide error. Signed-off-by: Yasuaki Ishimatsu Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Link: http://lkml.kernel.org/r/54475703.8000505@jp.fujitsu.com Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index fbc0b82..e9abd4e 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1530,7 +1530,7 @@ static void update_task_scan_period(struct task_struct *p, * scanning faster if shared accesses dominate as it may * simply bounce migrations uselessly */ - ratio = DIV_ROUND_UP(private * NUMA_PERIOD_SLOTS, (private + shared)); + ratio = DIV_ROUND_UP(private * NUMA_PERIOD_SLOTS, (private + shared + 1)); diff = (diff * ratio) / NUMA_PERIOD_SLOTS; } -- 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/