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=-19.4 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, URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 75C7EC11F6F for ; Mon, 12 Jul 2021 06:52:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 62BFD611BF for ; Mon, 12 Jul 2021 06:52:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239660AbhGLGz3 (ORCPT ); Mon, 12 Jul 2021 02:55:29 -0400 Received: from mail.kernel.org ([198.145.29.99]:36734 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235146AbhGLGkV (ORCPT ); Mon, 12 Jul 2021 02:40:21 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 11351601FC; Mon, 12 Jul 2021 06:37:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1626071853; bh=3uHYnLLbvUx2zPCMjBCstSOkG53B06PjDc4sN75xqyg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=qv59wt1D92eeZAAqvWwLgr3lMoRuL3oGwVkUuyIRTeXlyfUSyJZeM0CXpsl5+nd98 xKsHOfQo0LKcM5iTVRaekXh+5HHZoBfn9PKr27jXtDQ7GFFECSQWRR6aapgYaF/C2X Mo/RDiInKMMU8hqw0v0BLtd9lsyB6A9WXq1k2OuY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Petr Mladek , Oleg Nesterov , Nathan Chancellor , Nick Desaulniers , Tejun Heo , Minchan Kim , jenhaochen@google.com, Martin Liu , Andrew Morton , Linus Torvalds , Sasha Levin Subject: [PATCH 5.10 206/593] kthread_worker: fix return value when kthread_mod_delayed_work() races with kthread_cancel_delayed_work_sync() Date: Mon, 12 Jul 2021 08:06:06 +0200 Message-Id: <20210712060905.642968921@linuxfoundation.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210712060843.180606720@linuxfoundation.org> References: <20210712060843.180606720@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: linux-kernel@vger.kernel.org From: Petr Mladek [ Upstream commit d71ba1649fa3c464c51ec7163e4b817345bff2c7 ] kthread_mod_delayed_work() might race with kthread_cancel_delayed_work_sync() or another kthread_mod_delayed_work() call. The function lets the other operation win when it sees work->canceling counter set. And it returns @false. But it should return @true as it is done by the related workqueue API, see mod_delayed_work_on(). The reason is that the return value might be used for reference counting. It has to distinguish the case when the number of queued works has changed or stayed the same. The change is safe. kthread_mod_delayed_work() return value is not checked anywhere at the moment. Link: https://lore.kernel.org/r/20210521163526.GA17916@redhat.com Link: https://lkml.kernel.org/r/20210610133051.15337-4-pmladek@suse.com Signed-off-by: Petr Mladek Reported-by: Oleg Nesterov Cc: Nathan Chancellor Cc: Nick Desaulniers Cc: Tejun Heo Cc: Minchan Kim Cc: Cc: Martin Liu Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- kernel/kthread.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) diff --git a/kernel/kthread.c b/kernel/kthread.c index 36be4364b313..9825cf89c614 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -1107,14 +1107,14 @@ static bool __kthread_cancel_work(struct kthread_work *work) * modify @dwork's timer so that it expires after @delay. If @delay is zero, * @work is guaranteed to be queued immediately. * - * Return: %true if @dwork was pending and its timer was modified, - * %false otherwise. + * Return: %false if @dwork was idle and queued, %true otherwise. * * A special case is when the work is being canceled in parallel. * It might be caused either by the real kthread_cancel_delayed_work_sync() * or yet another kthread_mod_delayed_work() call. We let the other command - * win and return %false here. The caller is supposed to synchronize these - * operations a reasonable way. + * win and return %true here. The return value can be used for reference + * counting and the number of queued works stays the same. Anyway, the caller + * is supposed to synchronize these operations a reasonable way. * * This function is safe to call from any context including IRQ handler. * See __kthread_cancel_work() and kthread_delayed_work_timer_fn() @@ -1126,13 +1126,15 @@ bool kthread_mod_delayed_work(struct kthread_worker *worker, { struct kthread_work *work = &dwork->work; unsigned long flags; - int ret = false; + int ret; raw_spin_lock_irqsave(&worker->lock, flags); /* Do not bother with canceling when never queued. */ - if (!work->worker) + if (!work->worker) { + ret = false; goto fast_queue; + } /* Work must not be used with >1 worker, see kthread_queue_work() */ WARN_ON_ONCE(work->worker != worker); @@ -1150,8 +1152,11 @@ bool kthread_mod_delayed_work(struct kthread_worker *worker, * be used for reference counting. */ kthread_cancel_delayed_work_timer(work, &flags); - if (work->canceling) + if (work->canceling) { + /* The number of works in the queue does not change. */ + ret = true; goto out; + } ret = __kthread_cancel_work(work); fast_queue: -- 2.30.2