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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,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 D685FC11D3D for ; Thu, 27 Feb 2020 19:18:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B670724680 for ; Thu, 27 Feb 2020 19:18:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730125AbgB0TSK (ORCPT ); Thu, 27 Feb 2020 14:18:10 -0500 Received: from outbound-smtp26.blacknight.com ([81.17.249.194]:41420 "EHLO outbound-smtp26.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729418AbgB0TSJ (ORCPT ); Thu, 27 Feb 2020 14:18:09 -0500 Received: from mail.blacknight.com (pemlinmail05.blacknight.ie [81.17.254.26]) by outbound-smtp26.blacknight.com (Postfix) with ESMTPS id 15F3CCAB1D for ; Thu, 27 Feb 2020 19:18:07 +0000 (GMT) Received: (qmail 21014 invoked from network); 27 Feb 2020 19:18:06 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.18.57]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 27 Feb 2020 19:18:06 -0000 Date: Thu, 27 Feb 2020 19:18:04 +0000 From: Mel Gorman To: Ingo Molnar Cc: Qian Cai , Peter Zijlstra , Juri Lelli , Steven Rostedt , Valentin Schneider , paulmck@kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] sched/numa: Acquire RCU lock for checking idle cores during NUMA balancing Message-ID: <20200227191804.GJ3818@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Qian Cai reported the following The linux-next commit ff7db0bf24db ("sched/numa: Prefer using an idle CPU as a migration target instead of comparing tasks") introduced a boot warning, [ 86.520534][ T1] WARNING: suspicious RCU usage [ 86.520540][ T1] 5.6.0-rc3-next-20200227 #7 Not tainted [ 86.520545][ T1] ----------------------------- [ 86.520551][ T1] kernel/sched/fair.c:5914 suspicious rcu_dereference_check() usage! [ 86.520555][ T1] [ 86.520555][ T1] other info that might help us debug this: [ 86.520555][ T1] [ 86.520561][ T1] [ 86.520561][ T1] rcu_scheduler_active = 2, debug_locks = 1 [ 86.520567][ T1] 1 lock held by systemd/1: [ 86.520571][ T1] #0: ffff8887f4b14848 (&mm->mmap_sem#2){++++}, at: do_page_fault+0x1d2/0x998 [ 86.520594][ T1] [ 86.520594][ T1] stack backtrace: [ 86.520602][ T1] CPU: 1 PID: 1 Comm: systemd Not tainted 5.6.0-rc3-next-20200227 #7 task_numa_migrate() checks for idle cores when updating NUMA-related statistics. This relies on reading a RCU-protected structure in test_idle_cores() via this call chain task_numa_migrate -> update_numa_stats -> numa_idle_core -> test_idle_cores While the locking could be fine-grained, it is more appropriate to acquire the RCU lock for the entire scan of the domain. This patch removes the warning triggered at boot time. Fixes: ff7db0bf24db ("sched/numa: Prefer using an idle CPU as a migration target instead of comparing tasks") Reported-by: Qian Cai Signed-off-by: Mel Gorman --- kernel/sched/fair.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 10f9e6729fcf..1592b6d26239 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1595,6 +1595,7 @@ static void update_numa_stats(struct task_numa_env *env, memset(ns, 0, sizeof(*ns)); ns->idle_cpu = -1; + rcu_read_lock(); for_each_cpu(cpu, cpumask_of_node(nid)) { struct rq *rq = cpu_rq(cpu); @@ -1614,6 +1615,7 @@ static void update_numa_stats(struct task_numa_env *env, idle_core = numa_idle_core(idle_core, cpu); } } + rcu_read_unlock(); ns->weight = cpumask_weight(cpumask_of_node(nid));