From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0D482C433EF for ; Mon, 18 Jun 2018 09:16:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 88D2A208D5 for ; Mon, 18 Jun 2018 09:16:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 88D2A208D5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966789AbeFRJQn (ORCPT ); Mon, 18 Jun 2018 05:16:43 -0400 Received: from out30-131.freemail.mail.aliyun.com ([115.124.30.131]:41924 "EHLO out30-131.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965495AbeFRJQk (ORCPT ); Mon, 18 Jun 2018 05:16:40 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R861e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04455;MF=xlpang@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0T2wux.s_1529313378; Received: from localhost(mailfrom:xlpang@linux.alibaba.com fp:SMTPD_---0T2wux.s_1529313378) by smtp.aliyun-inc.com(127.0.0.1); Mon, 18 Jun 2018 17:16:35 +0800 From: Xunlei Pang To: Peter Zijlstra , Ingo Molnar , Ben Segall Cc: linux-kernel@vger.kernel.org Subject: [PATCH 1/2] sched/fair: Fix bandwidth timer clock drift condition Date: Mon, 18 Jun 2018 17:16:17 +0800 Message-Id: <20180618091618.21480-1-xlpang@linux.alibaba.com> X-Mailer: git-send-email 2.14.1.40.g8e62ba1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The current condition to judge clock drift in expire_cfs_rq_runtime() is wrong, the two runtime_expires are actually the same when clock drift happens, so this condtion can never hit. The orginal design was correctly done by commit a9cf55b28610 ("sched: Expire invalid runtime"), but was changed to be the current one due to its locking issue. This patch introduces another way, it adds a new field in both structure cfs_rq and cfs_bandwidth to record the expiration update sequence, and use them to figure out if clock drift happens(true if they equal). This fix is also needed by the following patch. Fixes: 51f2176d74ac ("sched/fair: Fix unlocked reads of some cfs_b->quota/period") Cc: Ben Segall Signed-off-by: Xunlei Pang --- kernel/sched/fair.c | 14 ++++++++------ kernel/sched/sched.h | 6 ++++-- 2 files changed, 12 insertions(+), 8 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index e497c05aab7f..9f384264e832 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4590,6 +4590,7 @@ void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b) now = sched_clock_cpu(smp_processor_id()); cfs_b->runtime = cfs_b->quota; cfs_b->runtime_expires = now + ktime_to_ns(cfs_b->period); + cfs_b->expires_seq++; } static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg) @@ -4612,6 +4613,7 @@ static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq) struct task_group *tg = cfs_rq->tg; struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg); u64 amount = 0, min_amount, expires; + int expires_seq; /* note: this is a positive sum as runtime_remaining <= 0 */ min_amount = sched_cfs_bandwidth_slice() - cfs_rq->runtime_remaining; @@ -4629,6 +4631,7 @@ static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq) } } expires = cfs_b->runtime_expires; + expires_seq = cfs_b->expires_seq; raw_spin_unlock(&cfs_b->lock); cfs_rq->runtime_remaining += amount; @@ -4637,8 +4640,10 @@ static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq) * spread between our sched_clock and the one on which runtime was * issued. */ - if ((s64)(expires - cfs_rq->runtime_expires) > 0) + if ((s64)(expires - cfs_rq->runtime_expires) > 0) { cfs_rq->runtime_expires = expires; + cfs_rq->expires_seq = expires_seq; + } return cfs_rq->runtime_remaining > 0; } @@ -4664,12 +4669,9 @@ static void expire_cfs_rq_runtime(struct cfs_rq *cfs_rq) * has not truly expired. * * Fortunately we can check determine whether this the case by checking - * whether the global deadline has advanced. It is valid to compare - * cfs_b->runtime_expires without any locks since we only care about - * exact equality, so a partial write will still work. + * whether the global deadline(cfs_b->expires_seq) has advanced. */ - - if (cfs_rq->runtime_expires != cfs_b->runtime_expires) { + if (cfs_rq->expires_seq == cfs_b->expires_seq) { /* extend local deadline, drift is bounded above by 2 ticks */ cfs_rq->runtime_expires += TICK_NSEC; } else { diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 6601baf2361c..e977e04f8daf 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -334,9 +334,10 @@ struct cfs_bandwidth { u64 runtime; s64 hierarchical_quota; u64 runtime_expires; + int expires_seq; - int idle; - int period_active; + short idle; + short period_active; struct hrtimer period_timer; struct hrtimer slack_timer; struct list_head throttled_cfs_rq; @@ -551,6 +552,7 @@ struct cfs_rq { #ifdef CONFIG_CFS_BANDWIDTH int runtime_enabled; + int expires_seq; u64 runtime_expires; s64 runtime_remaining; -- 2.14.1.40.g8e62ba1