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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS 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 94075C43381 for ; Thu, 7 Mar 2019 00:55:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5DABB20663 for ; Thu, 7 Mar 2019 00:55:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726226AbfCGAzL (ORCPT ); Wed, 6 Mar 2019 19:55:11 -0500 Received: from mx1.redhat.com ([209.132.183.28]:49374 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726010AbfCGAzL (ORCPT ); Wed, 6 Mar 2019 19:55:11 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E541681DE9; Thu, 7 Mar 2019 00:55:10 +0000 (UTC) Received: from jsavitz.bos.com (dhcp-17-166.bos.redhat.com [10.18.17.166]) by smtp.corp.redhat.com (Postfix) with ESMTP id F38A060C1B; Thu, 7 Mar 2019 00:55:09 +0000 (UTC) From: Joel Savitz To: linux-kernel@vger.kernel.org Cc: Joel Savitz , Li Zefan , cgroups@vger.kernel.org Subject: [PATCH] cpuset: restore sanity to cpuset_cpus_allowed_fallback() Date: Wed, 6 Mar 2019 19:54:48 -0500 Message-Id: <1551920088-30685-1-git-send-email-jsavitz@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Thu, 07 Mar 2019 00:55:10 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If a process is limited by taskset (i.e. cpuset) to only be allowed to run on cpu N, and then cpu N is offlined via hotplug, the process will be assigned the current value of its cpuset cgroup's effective_cpus field in a call to do_set_cpus_allowed() in cpuset_cpus_allowed_fallback(). This argument's value does not makes sense for this case, because task_cs(tsk)->effective_cpus is modified by cpuset_hotplug_workfn() to reflect the new value of cpu_active_mask after cpu N is removed from the mask. While this may make sense for the cgroup affinity mask, it does not make sense on a per-task basis, as a task that was previously limited to only be run on cpu N will be limited to every cpu _except_ for cpu N after it is offlined/onlined via hotplug. Pre-patch behavior: $ grep Cpus /proc/$$/status Cpus_allowed: ff Cpus_allowed_list: 0-7 $ taskset -p 4 $$ pid 19202's current affinity mask: f pid 19202's new affinity mask: 4 $ grep Cpus /proc/self/status Cpus_allowed: 04 Cpus_allowed_list: 2 # echo off > /sys/devices/system/cpu/cpu2/online $ grep Cpus /proc/$$/status Cpus_allowed: 0b Cpus_allowed_list: 0-1,3 # echo on > /sys/devices/system/cpu/cpu2/online $ grep Cpus /proc/$$/status Cpus_allowed: 0b Cpus_allowed_list: 0-1,3 On a patched system, the final grep produces the following output instead: $ grep Cpus /proc/$$/status Cpus_allowed: ff Cpus_allowed_list: 0-7 This patch changes the above behavior by instead simply resetting the mask to cpu_possible_mask. Signed-off-by: Joel Savitz --- kernel/cgroup/cpuset.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 479743db6c37..5f65a2167bdf 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -3243,7 +3243,7 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask) void cpuset_cpus_allowed_fallback(struct task_struct *tsk) { rcu_read_lock(); - do_set_cpus_allowed(tsk, task_cs(tsk)->effective_cpus); + do_set_cpus_allowed(tsk, cpu_possible_mask); rcu_read_unlock(); /* -- 2.20.1