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=-11.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 CDE39C4346E for ; Tue, 29 Sep 2020 09:56:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 506C5221E8 for ; Tue, 29 Sep 2020 09:56:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727660AbgI2J4p (ORCPT ); Tue, 29 Sep 2020 05:56:45 -0400 Received: from foss.arm.com ([217.140.110.172]:38940 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725468AbgI2J4p (ORCPT ); Tue, 29 Sep 2020 05:56:45 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id AEB8E31B; Tue, 29 Sep 2020 02:56:44 -0700 (PDT) Received: from [192.168.178.2] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 57AB63F6CF; Tue, 29 Sep 2020 02:56:43 -0700 (PDT) Subject: Re: [PATCH] sched,fair: use list_for_each_entry() in print_cfs_stats() To: Hui Su , mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, linux-kernel@vger.kernel.org References: <20200925191019.GA174025@rlk> From: Dietmar Eggemann Message-ID: <7afdceb2-b727-4f89-75e3-e08bf06d78d9@arm.com> Date: Tue, 29 Sep 2020 11:56:42 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200925191019.GA174025@rlk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25/09/2020 21:10, Hui Su wrote: > Macro for_each_leaf_cfs_rq_safe() use list_for_each_entry_safe(), > which can against removal of list entry, but we only > print the cfs_rq data and won't remove the list entry in > print_cfs_stats(). > > Thus, add macro for_each_leaf_cfs_rq() based on > list_for_each_entry(), and use for_each_leaf_cfs_rq() in > print_cfs_stats(). > > Signed-off-by: Hui Su > --- > kernel/sched/fair.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 1a68a0536add..d40dfb4349b0 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -391,11 +391,16 @@ static inline void assert_list_leaf_cfs_rq(struct rq *rq) > SCHED_WARN_ON(rq->tmp_alone_branch != &rq->leaf_cfs_rq_list); > } > > -/* Iterate thr' all leaf cfs_rq's on a runqueue */ > +/* Iterate thr' all leaf cfs_rq's on a runqueue safely */ > #define for_each_leaf_cfs_rq_safe(rq, cfs_rq, pos) \ > list_for_each_entry_safe(cfs_rq, pos, &rq->leaf_cfs_rq_list, \ > leaf_cfs_rq_list) > > +/* Iterate thr' all leaf cfs_rq's on a runqueue */ > +#define for_each_leaf_cfs_rq(rq, cfs_rq) \ > + list_for_each_entry(cfs_rq, &rq->leaf_cfs_rq_list, \ > + leaf_cfs_rq_list) > + > /* Do the two (enqueued) entities belong to the same group ? */ > static inline struct cfs_rq * > is_same_group(struct sched_entity *se, struct sched_entity *pse) > @@ -11185,10 +11190,10 @@ const struct sched_class fair_sched_class > #ifdef CONFIG_SCHED_DEBUG > void print_cfs_stats(struct seq_file *m, int cpu) > { > - struct cfs_rq *cfs_rq, *pos; > + struct cfs_rq *cfs_rq; > > rcu_read_lock(); > - for_each_leaf_cfs_rq_safe(cpu_rq(cpu), cfs_rq, pos) > + for_each_leaf_cfs_rq(cpu_rq(cpu), cfs_rq) > print_cfs_rq(m, cpu, cfs_rq); > rcu_read_unlock(); > } IMHO, for_each_leaf_cfs_rq_safe() was introduced in commit a9e7f6544b9c ("sched/fair: Fix O(nr_cgroups) in load balance path") and reintroduced again by commit 039ae8bcf7a5 ("sched/fair: Fix O(nr_cgroups) in the load balancing path") to prevent races between tasks running print_cfs_stats() and today's __update_blocked_fair() -> list_del_leaf_cfs_rq(cfs_rq). Your patch doesn't compile w/ !CONFIG_FAIR_GROUP_SCHED.