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=-19.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT 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 B4860C4361A for ; Mon, 15 Mar 2021 14:10:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 768BF64EFE for ; Mon, 15 Mar 2021 14:10:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234698AbhCOOJo (ORCPT ); Mon, 15 Mar 2021 10:09:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:51602 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234522AbhCOOEL (ORCPT ); Mon, 15 Mar 2021 10:04:11 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 0B85D64DAD; Mon, 15 Mar 2021 14:04:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1615817050; bh=qnQtDiodf1/hFwBBqCwObIlg53X0wpN0Hr3q0RR52+k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=YjWV1/8wLtMyxbsP37J6/96vGEte55MswkBHO8k9Ntegq57XkpyFVnBrCBjlRDbqk UraBQle47i4fXH7S+N439z0Tn6U3c6bsTBvDstlBVB5woId2pca8hxdXll39Qsggdn LCc1N8wP2d8iR9bH/S9Bhq9lhFFn/SoU41NvWCkg= From: gregkh@linuxfoundation.org To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, stable@kernel.org, "Peter Zijlstra (Intel)" , Ingo Molnar , Valentin Schneider Subject: [PATCH 5.11 275/306] sched: Simplify migration_cpu_stop() Date: Mon, 15 Mar 2021 14:55:38 +0100 Message-Id: <20210315135516.960898011@linuxfoundation.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210315135507.611436477@linuxfoundation.org> References: <20210315135507.611436477@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Greg Kroah-Hartman From: Peter Zijlstra commit c20cf065d4a619d394d23290093b1002e27dff86 upstream. When affine_move_task() issues a migration_cpu_stop(), the purpose of that function is to complete that @pending, not any random other p->migration_pending that might have gotten installed since. This realization much simplifies migration_cpu_stop() and allows further necessary steps to fix all this as it provides the guarantee that @pending's stopper will complete @pending (and not some random other @pending). Fixes: 6d337eab041d ("sched: Fix migrate_disable() vs set_cpus_allowed_ptr()") Cc: stable@kernel.org Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Valentin Schneider Link: https://lkml.kernel.org/r/20210224131355.430014682@infradead.org Signed-off-by: Greg Kroah-Hartman --- kernel/sched/core.c | 56 +++++++--------------------------------------------- 1 file changed, 8 insertions(+), 48 deletions(-) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1898,8 +1898,8 @@ static struct rq *__migrate_task(struct */ static int migration_cpu_stop(void *data) { - struct set_affinity_pending *pending; struct migration_arg *arg = data; + struct set_affinity_pending *pending = arg->pending; struct task_struct *p = arg->task; int dest_cpu = arg->dest_cpu; struct rq *rq = this_rq(); @@ -1921,25 +1921,6 @@ static int migration_cpu_stop(void *data raw_spin_lock(&p->pi_lock); rq_lock(rq, &rf); - pending = p->migration_pending; - if (pending && !arg->pending) { - /* - * This happens from sched_exec() and migrate_task_to(), - * neither of them care about pending and just want a task to - * maybe move about. - * - * Even if there is a pending, we can ignore it, since - * affine_move_task() will have it's own stop_work's in flight - * which will manage the completion. - * - * Notably, pending doesn't need to match arg->pending. This can - * happen when tripple concurrent affine_move_task() first sets - * pending, then clears pending and eventually sets another - * pending. - */ - pending = NULL; - } - /* * If task_rq(p) != rq, it cannot be migrated here, because we're * holding rq->lock, if p->on_rq == 0 it cannot get enqueued because @@ -1950,31 +1931,20 @@ static int migration_cpu_stop(void *data goto out; if (pending) { - p->migration_pending = NULL; + if (p->migration_pending == pending) + p->migration_pending = NULL; complete = true; } - /* migrate_enable() -- we must not race against SCA */ - if (dest_cpu < 0) { - /* - * When this was migrate_enable() but we no longer - * have a @pending, a concurrent SCA 'fixed' things - * and we should be valid again. Nothing to do. - */ - if (!pending) { - WARN_ON_ONCE(!cpumask_test_cpu(task_cpu(p), &p->cpus_mask)); - goto out; - } - + if (dest_cpu < 0) dest_cpu = cpumask_any_distribute(&p->cpus_mask); - } if (task_on_rq_queued(p)) rq = __migrate_task(rq, &rf, p, dest_cpu); else p->wake_cpu = dest_cpu; - } else if (dest_cpu < 0 || pending) { + } else if (pending) { /* * This happens when we get migrated between migrate_enable()'s * preempt_enable() and scheduling the stopper task. At that @@ -1989,23 +1959,14 @@ static int migration_cpu_stop(void *data * ->pi_lock, so the allowed mask is stable - if it got * somewhere allowed, we're done. */ - if (pending && cpumask_test_cpu(task_cpu(p), p->cpus_ptr)) { - p->migration_pending = NULL; + if (cpumask_test_cpu(task_cpu(p), p->cpus_ptr)) { + if (p->migration_pending == pending) + p->migration_pending = NULL; complete = true; goto out; } /* - * When this was migrate_enable() but we no longer have an - * @pending, a concurrent SCA 'fixed' things and we should be - * valid again. Nothing to do. - */ - if (!pending) { - WARN_ON_ONCE(!cpumask_test_cpu(task_cpu(p), &p->cpus_mask)); - goto out; - } - - /* * When migrate_enable() hits a rq mis-match we can't reliably * determine is_migration_disabled() and so have to chase after * it. @@ -2022,7 +1983,6 @@ out: complete_all(&pending->done); /* For pending->{arg,stop_work} */ - pending = arg->pending; if (pending && refcount_dec_and_test(&pending->refs)) wake_up_var(&pending->refs);