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=-9.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,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 97F55C433DF for ; Thu, 15 Oct 2020 09:14:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 450AD2224A for ; Thu, 15 Oct 2020 09:14:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730545AbgJOJOe (ORCPT ); Thu, 15 Oct 2020 05:14:34 -0400 Received: from foss.arm.com ([217.140.110.172]:50114 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726185AbgJOJOd (ORCPT ); Thu, 15 Oct 2020 05:14:33 -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 E9CC6D6E; Thu, 15 Oct 2020 02:14:32 -0700 (PDT) Received: from e113632-lin (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EC8803F66B; Thu, 15 Oct 2020 02:14:30 -0700 (PDT) References: <20201005145717.346020688@infradead.org> <20201013140116.26651-1-valentin.schneider@arm.com> <20201013141508.u7saiudjyuvihvcx@linutronix.de> <20201013142108.GD2594@hirez.programming.kicks-ass.net> User-agent: mu4e 0.9.17; emacs 26.3 From: Valentin Schneider To: Peter Zijlstra Cc: Sebastian Andrzej Siewior , linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@kernel.org, qais.yousef@arm.com, swood@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vincent.donnefort@arm.com, tj@kernel.org Subject: Re: [PATCH 1/2] sched: Deny self-issued __set_cpus_allowed_ptr() when migrate_disable() In-reply-to: <20201013142108.GD2594@hirez.programming.kicks-ass.net> Date: Thu, 15 Oct 2020 10:14:05 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13/10/20 15:21, Peter Zijlstra wrote: > On Tue, Oct 13, 2020 at 04:15:08PM +0200, Sebastian Andrzej Siewior wrote: >> On 2020-10-13 15:01:15 [+0100], Valentin Schneider wrote: >> > migrate_disable(); >> > set_cpus_allowed_ptr(current, {something excluding task_cpu(current)}); >> > affine_move_task(); <-- never returns >> > >> > Signed-off-by: Valentin Schneider >> > --- >> > kernel/sched/core.c | 5 +++++ >> > 1 file changed, 5 insertions(+) >> > >> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> > index 4ccd1099adaa..7f4e38819de1 100644 >> > --- a/kernel/sched/core.c >> > +++ b/kernel/sched/core.c >> > @@ -2189,6 +2189,11 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, >> > if (!(flags & SCA_MIGRATE_ENABLE) && cpumask_equal(&p->cpus_mask, new_mask)) >> > goto out; >> > >> > + if (p == current && >> > + is_migration_disabled(p) && >> > + !cpumask_test_cpu(task_cpu(p), new_mask)) >> > + ret = -EBUSY; >> > + >> >> This shouldn't happen, right? The function may sleep so it shouldn't be >> entered with disabled migration. A WARN_ON might spot the bad caller. > > So yeah, I like detecting the case but agree with bigeasy that an > additional WARN would make sense, lemme go add that. Err, I've just realized that this will warn on migrate_enable() if there are pending affinity changes, since p->migration_disabled is cleared *after* the call to __set_cpus_allowed_ptr(). This wants: --- diff --git a/kernel/sched/core.c b/kernel/sched/core.c index d503d6cb8350..e8156e3d3b4a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2266,7 +2266,8 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, if (!(flags & SCA_MIGRATE_ENABLE) && cpumask_equal(&p->cpus_mask, new_mask)) goto out; - if (WARN_ON_ONCE(p == current && + if (WARN_ON_ONCE(!(flags & SCA_MIGRATE_ENABLE) && + p == current && is_migration_disabled(p) && !cpumask_test_cpu(task_cpu(p), new_mask))) ret = -EBUSY; ---