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=-15.5 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 BA976C07E99 for ; Fri, 9 Jul 2021 14:18:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9643C613B5 for ; Fri, 9 Jul 2021 14:18:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232144AbhGIOVQ (ORCPT ); Fri, 9 Jul 2021 10:21:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57930 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231797AbhGIOVP (ORCPT ); Fri, 9 Jul 2021 10:21:15 -0400 Received: from mail-io1-xd31.google.com (mail-io1-xd31.google.com [IPv6:2607:f8b0:4864:20::d31]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BB3F8C0613DD for ; Fri, 9 Jul 2021 07:18:31 -0700 (PDT) Received: by mail-io1-xd31.google.com with SMTP id l5so12551870iok.7 for ; Fri, 09 Jul 2021 07:18:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=KCLoDkkZnsfCEVph7CiGHPbNElkGreiJown+HOpz3Qs=; b=uhWTZf1E4fA+aW1yeP3TZedffaA9AQt0sRu99VSXttjpMhs/jTS9Cmt0UvPzN5s7s4 CoJs5Nfl+g68w8+8OpXv1AB5W7OUhwILNinr4pQ4oouOBjonVhlgJgRA1KnJOUvET5Ih shav5mbMhmRVFCZg026/fts9fvR3fxaU1/7abqcYd3DwqguizRd4KvfoW352zR5pHo6y fAOCUEAE9rXDaTS604JfwaO7GLI0gI5J+Wuh805TWwF2J/HKBZNdsp4hYgXGSO1PJixf NLAfmCHe54JLkW7Acx2AHK3X8V9DARw09gYv2vuIc6tPjQaB3A3GC/BpmMhXHOvn23ET szBA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=KCLoDkkZnsfCEVph7CiGHPbNElkGreiJown+HOpz3Qs=; b=oEv5Covdnkeo4sBphcpKOZUtJewv54Kx7EI3uqwOx/f5Kd8hdC1uAQFl+K7SlMJhrc yCHvUM70ksS0jskn9B3N1sEPS5eO4WFvKnOnSivIKrCSO83aWKJ785RLaz3cjCLXT33f CVGfNrq2hnmQ2+6ekXqOkSwz4GVRv5MhyWcaNeaAXFxS5kgQNMffRsBjiNWC7DnHsU2v 3yRfWLACE0kDMnRi4m8fSc96yAdmJ7amH5N+d17Z6HABk8hhsHxLgZYGwfkDb2c4949t M+vA8ZwH3jQoADiKYKkItMZDR9uHQAE2MmrpnUTTerBqThFgmPGQ1X4nLouWmsm7XLfS xatA== X-Gm-Message-State: AOAM532gaADwlOl6eLKvzPJa7/TrjB+XSOqjxiOSgwtBy3ZYRwrcBw96 Dg2gGcvEdPgtuqml1NaJF8E+E3mSTYQ1YQ== X-Google-Smtp-Source: ABdhPJygcmrftMzhupUiWoYDNlEDOHdmH6yuCFUQEgnY/Uq3BmA2o/TeNCfQkVOEv8W8Ek+OVpS0gA== X-Received: by 2002:a05:6638:4109:: with SMTP id ay9mr4130608jab.81.1625840310893; Fri, 09 Jul 2021 07:18:30 -0700 (PDT) Received: from [192.168.1.134] ([198.8.77.61]) by smtp.gmail.com with ESMTPSA id e5sm3078212ilu.15.2021.07.09.07.18.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 09 Jul 2021 07:18:30 -0700 (PDT) Subject: Re: [PATCH] task_work: return -EBUSY when adding same work To: yaozhenguo , oleg@redhat.comm Cc: linux-kernel@vger.kernel.org, yaozhenguo@jd.com References: <20210709122712.42844-1-yaozhenguo1@gmail.com> From: Jens Axboe Message-ID: <872612b5-b9c6-43aa-a167-1c204d0f1c5a@kernel.dk> Date: Fri, 9 Jul 2021 08:18:27 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210709122712.42844-1-yaozhenguo1@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/9/21 6:27 AM, yaozhenguo wrote: > when same work is added to task->task_works list one by one, > the list becomes endless loop. So return -EBUSY when this > situation happen. > > Signed-off-by: yaozhenguo > --- > kernel/task_work.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/kernel/task_work.c b/kernel/task_work.c > index 1698fbe..5061ebf 100644 > --- a/kernel/task_work.c > +++ b/kernel/task_work.c > @@ -27,7 +27,7 @@ > * list is LIFO. > * > * RETURNS: > - * 0 if succeeds or -ESRCH. > + * 0 if succeeds or -ESRCH, -EBUSY. > */ > int task_work_add(struct task_struct *task, struct callback_head *work, > enum task_work_notify_mode notify) > @@ -41,6 +41,8 @@ int task_work_add(struct task_struct *task, struct callback_head *work, > head = READ_ONCE(task->task_works); > if (unlikely(head == &work_exited)) > return -ESRCH; > + if (unlikely(head == work)) > + return -EBUSY; > work->next = head; > } while (cmpxchg(&task->task_works, head, work) != head); I don't think there's anything conceptually wrong with this patch, but it makes me think that you hit this condition. It's really a bug in the caller, of course, is a WARN_ON_ONCE() warranted here? And who was the caller? -- Jens Axboe