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=-13.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,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 02821C47094 for ; Thu, 10 Jun 2021 13:31:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DFED661403 for ; Thu, 10 Jun 2021 13:31:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231218AbhFJNc6 (ORCPT ); Thu, 10 Jun 2021 09:32:58 -0400 Received: from smtp-out1.suse.de ([195.135.220.28]:40078 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230413AbhFJNc5 (ORCPT ); Thu, 10 Jun 2021 09:32:57 -0400 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 18CF421996; Thu, 10 Jun 2021 13:31:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1623331860; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=EgJC45Dypvp92B1Ue8sTD50N06sDV0MZrg+QBunGi30=; b=q0MaF8Z9GMMrSUwqI+mhwH+Jlw9PwRamEyTXv/+vt8RrPEW3icKsik9ABSqVWqljMWjtEX xOqWt1pvDP7taIOe/D6sHtw2gy5GOyHTWdo8Z5gI1dMeIkTRRG1bOSKrZRG//NnMEGf160 zgGdxg1mU/pkwyjWsPGtZdIPl/XznOQ= Received: from alley.suse.cz (unknown [10.100.224.162]) by relay2.suse.de (Postfix) with ESMTP id C36CAA3B8A; Thu, 10 Jun 2021 13:30:59 +0000 (UTC) From: Petr Mladek To: Andrew Morton , Martin Liu Cc: Oleg Nesterov , Nathan Chancellor , Nick Desaulniers , Tejun Heo , minchan@google.com, davidchao@google.com, jenhaochen@google.com, clang-built-linux@googlegroups.com, linux-kernel@vger.kernel.org, Petr Mladek Subject: [PATCH 0/3] kthread_worker: Fix race between kthread_mod_delayed_work() and kthread_cancel_delayed_work_sync() Date: Thu, 10 Jun 2021 15:30:48 +0200 Message-Id: <20210610133051.15337-1-pmladek@suse.com> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patchset fixes the race between kthread_mod_delayed_work() and kthread_cancel_delayed_work_sync() including proper return value handling. The original fix, from Martin Liu [1], opened discussion [2] about the return value. It took me some time to realize that the original patch was not a correct fix. The problem is that the return value might be used for reference counting of the queued works. The return value is boolean. It could distinguish only two situations where the work is: + newly queued => inc(refcnt) (ret == false) + was queued, removed, added => nope(refcntn) (ret == true) The original fix, introduced another situation: + was queued, removed => dec(refcnt) (ret == ???) The proper solution is to remove the work from the list only when it can be added again. Fortunately, it can be fixed relatively easily. I have split it into 3 small steps. [1] https://lore.kernel.org/r/20210513065458.941403-1-liumartin@google.com [2] https://lore.kernel.org/r/20210520214737.MrGGKbPrJ%akpm@linux-foundation.org Petr Mladek (3): kthread_worker: Split code for canceling the delayed work timer. kthread: Prevent deadlock when kthread_mod_delayed_work() races with kthread_cancel_delayed_work_sync() kthread_worker: Fix return value when kthread_mod_delayed_work() races with kthread_cancel_delayed_work_sync() kernel/kthread.c | 96 +++++++++++++++++++++++++++++++----------------- 1 file changed, 63 insertions(+), 33 deletions(-) -- 2.26.2