Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751569AbaJPJtT (ORCPT ); Thu, 16 Oct 2014 05:49:19 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:40015 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751194AbaJPJtR (ORCPT ); Thu, 16 Oct 2014 05:49:17 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v2.0.1 X-SHieldMailCheckerPolicyVersion: FJ-ISEC-20120718-3 Message-ID: <543F945F.4020303@jp.fujitsu.com> Date: Thu, 16 Oct 2014 18:48:15 +0900 From: Yasuaki Ishimatsu User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: , CC: , , , Subject: [PATCH v2] sched/fair: Care divide error in update_task_scan_period() Content-Type: text/plain; charset="ISO-2022-JP" Content-Transfer-Encoding: 7bit X-SecurityPolicyCheck-GC: OK by FENCE-Mail X-TM-AS-MML: No Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. By this patch, when both of private and shared are set to 0, denominator is set to 1 for avoiding divide error. Signed-off-by: Yasuaki Ishimatsu CC: Wanpeng Li CC: Rik van Riel CC: Peter Zijlstra --- kernel/sched/fair.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index bfa3c86..580fc74 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1466,6 +1466,7 @@ static void update_task_scan_period(struct task_struct *p, unsigned long remote = p->numa_faults_locality[0]; unsigned long local = p->numa_faults_locality[1]; + unsigned long total_faults = shared + private; /* * If there were no record hinting faults then either the task is @@ -1496,6 +1497,14 @@ static void update_task_scan_period(struct task_struct *p, slot = 1; diff = slot * period_slot; } else { + /* + * This is a rare case. total_faults might become 0 after + * offlining node. In this case, total_faults is set to 1 + * for avoiding divide error. + */ + if (unlikely(total_faults == 0)) + total_faults = 1; + diff = -(NUMA_PERIOD_THRESHOLD - ratio) * period_slot; /* @@ -1506,7 +1515,7 @@ 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, (total_faults)); diff = (diff * ratio) / NUMA_PERIOD_SLOTS; } -- 1.8.3.1 -- 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/