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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 F17B7C433DF for ; Thu, 15 Oct 2020 13:55:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9EA792222B for ; Thu, 15 Oct 2020 13:55:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387892AbgJONzC (ORCPT ); Thu, 15 Oct 2020 09:55:02 -0400 Received: from foss.arm.com ([217.140.110.172]:44636 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729679AbgJONzC (ORCPT ); Thu, 15 Oct 2020 09:55:02 -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 B750B13D5; Thu, 15 Oct 2020 06:55:01 -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 9DD3A3F719; Thu, 15 Oct 2020 06:54:59 -0700 (PDT) References: <20201015110532.738127234@infradead.org> <20201015110923.910090294@infradead.org> User-agent: mu4e 0.9.17; emacs 26.3 From: Valentin Schneider To: Peter Zijlstra Cc: tglx@linutronix.de, mingo@kernel.org, linux-kernel@vger.kernel.org, bigeasy@linutronix.de, 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, ouwen210@hotmail.com Subject: Re: [PATCH v3 10/19] sched: Fix migrate_disable() vs set_cpus_allowed_ptr() In-reply-to: <20201015110923.910090294@infradead.org> Date: Thu, 15 Oct 2020 14:54:53 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15/10/20 12:05, Peter Zijlstra wrote: > +static int affine_move_task(struct rq *rq, struct rq_flags *rf, > + struct task_struct *p, int dest_cpu, unsigned int flags) > +{ > + struct set_affinity_pending my_pending = { }, *pending = NULL; > + struct migration_arg arg = { > + .task = p, > + .dest_cpu = dest_cpu, > + }; > + bool complete = false; > + > + /* Can the task run on the task's current CPU? If so, we're done */ > + if (cpumask_test_cpu(task_cpu(p), &p->cpus_mask)) { > + pending = p->migration_pending; > + if (pending) { > + p->migration_pending = NULL; > + complete = true; Deciphering my TLA+ deadlock traces leads me to think this needs refcount_inc(&pending->refs); because the 'goto do_complete' leads us to an unconditional decrement. > + } > + task_rq_unlock(rq, p, rf); > + > + if (complete) > + goto do_complete; ^^^^ that here > + > + return 0; > + } > + [...] > +do_complete: > + if (complete) > + complete_all(&pending->done); > + } > + > + wait_for_completion(&pending->done); > + > + if (refcount_dec_and_test(&pending->refs)) ^^^^^^^^^^^^^^^^^^^^^^^ leads to this guy there > + wake_up_var(&pending->refs); > + > + wait_var_event(&my_pending.refs, !refcount_read(&my_pending.refs)); > + > + return 0; > +}