From patchwork Mon Mar 15 13:55:35 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 401163 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 7D67AC43381 for ; Mon, 15 Mar 2021 14:10:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5834464EEC for ; Mon, 15 Mar 2021 14:10:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230378AbhCOOJg (ORCPT ); Mon, 15 Mar 2021 10:09:36 -0400 Received: from mail.kernel.org ([198.145.29.99]:51244 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233634AbhCOOEF (ORCPT ); Mon, 15 Mar 2021 10:04:05 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id AD1C964F26; Mon, 15 Mar 2021 14:04:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1615817044; bh=w3kA6KVD8oO3i6qdq7ots3lG0U0fsVTt5Oda33Ydt6s=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=VbEW+RtJJ007iEIWCWT9FrL+nadGONNVS0zUITw1Jqr0mAGzAZ/1nd97yxMzS9Rvo brYGa5IMttsrKpybnzKvWU76Rv0BybJX9Cs2camF3KDxkT/vPShYktI5caX4ZYw9Nn mXCdlSmDyPktSsyIdhjkMLMWloD/5Re+jaaBY0Zc= 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 5.11 272/306] sched: Fix migration_cpu_stop() requeueing Date: Mon, 15 Mar 2021 14:55:35 +0100 Message-Id: <20210315135516.857766425@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 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Greg Kroah-Hartman From: Peter Zijlstra commit 8a6edb5257e2a84720fe78cb179eca58ba76126f upstream. When affine_move_task(p) is called on a running task @p, which is not otherwise already changing affinity, we'll first set p->migration_pending and then do: stop_one_cpu(cpu_of_rq(rq), migration_cpu_stop, &arg); This then gets us to migration_cpu_stop() running on the CPU that was previously running our victim task @p. If we find that our task is no longer on that runqueue (this can happen because of a concurrent migration due to load-balance etc.), then we'll end up at the: } else if (dest_cpu < 1 || pending) { branch. Which we'll take because we set pending earlier. Here we first check if the task @p has already satisfied the affinity constraints, if so we bail early [A]. Otherwise we'll reissue migration_cpu_stop() onto the CPU that is now hosting our task @p: stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop, &pending->arg, &pending->stop_work); Except, we've never initialized pending->arg, which will be all 0s. This then results in running migration_cpu_stop() on the next CPU with arg->p == NULL, which gives the by now obvious result of fireworks. The cure is to change affine_move_task() to always use pending->arg, furthermore we can use the exact same pattern as the SCA_MIGRATE_ENABLE case, since we'll block on the pending->done completion anyway, no point in adding yet another completion in stop_one_cpu(). This then gives a clear distinction between the two migration_cpu_stop() use cases: - sched_exec() / migrate_task_to() : arg->pending == NULL - affine_move_task() : arg->pending != NULL; And we can have it ignore p->migration_pending when !arg->pending. Any stop work from sched_exec() / migrate_task_to() is in addition to stop works from affine_move_task(), which will be sufficient to issue the completion. 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/20210224131355.357743989@infradead.org Signed-off-by: Greg Kroah-Hartman --- kernel/sched/core.c | 39 ++++++++++++++++++++++++++++----------- 1 file changed, 28 insertions(+), 11 deletions(-) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1922,6 +1922,24 @@ static int migration_cpu_stop(void *data 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 @@ -2194,10 +2212,6 @@ static int affine_move_task(struct rq *r 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 */ @@ -2235,6 +2249,12 @@ static int affine_move_task(struct rq *r /* Install the request */ refcount_set(&my_pending.refs, 1); init_completion(&my_pending.done); + my_pending.arg = (struct migration_arg) { + .task = p, + .dest_cpu = -1, /* any */ + .pending = &my_pending, + }; + p->migration_pending = &my_pending; } else { pending = p->migration_pending; @@ -2265,12 +2285,6 @@ static int affine_move_task(struct rq *r p->migration_flags &= ~MDF_PUSH; task_rq_unlock(rq, p, rf); - pending->arg = (struct migration_arg) { - .task = p, - .dest_cpu = -1, - .pending = pending, - }; - stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop, &pending->arg, &pending->stop_work); @@ -2283,8 +2297,11 @@ static int affine_move_task(struct rq *r * is_migration_disabled(p) checks to the stopper, which will * run on the same CPU as said p. */ + refcount_inc(&pending->refs); /* pending->{arg,stop_work} */ task_rq_unlock(rq, p, rf); - stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg); + + stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop, + &pending->arg, &pending->stop_work); } else {