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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 7B97BC433B4 for ; Thu, 22 Apr 2021 03:54:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4388761445 for ; Thu, 22 Apr 2021 03:54:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230319AbhDVDzH (ORCPT ); Wed, 21 Apr 2021 23:55:07 -0400 Received: from mail-pg1-f175.google.com ([209.85.215.175]:38666 "EHLO mail-pg1-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229536AbhDVDzH (ORCPT ); Wed, 21 Apr 2021 23:55:07 -0400 Received: by mail-pg1-f175.google.com with SMTP id w10so31908337pgh.5 for ; Wed, 21 Apr 2021 20:54:33 -0700 (PDT) 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=f0GPld9gZM6QCZw7uMJ7EaQFQMbW/T90wzQnT565wXg=; b=JU4nNrDP5Kj7xyz0Z7OcBz429PFFcOFKbio7lQGdSgFiqxEaSaWzOYAsJ9SEtBwfCu l3jm4abppIH7bw4RVx0R8ATD6bSS9kqPjJxyBcYbZ1jOXdqOG2HocjpuGeNZgxrCTYF3 yK/q3cWCf6uXZ7ZzgCiwlw8hiGNSr56hqudoF21fPbnqohSh5C+jXjWBzQkvBUzI2/+/ TFpu+c3YtVq0DvQsI+Hby93fTGjvCR3o9qWfAypc5m5UQPsKlhzqXwy/Feuh2TKYt4dY xoAErnQdS53KOGcTdPJtfgGkwQitlob6qGFtMUPrSry41H07oCVI86lSAulb9LIXgKka k7nQ== X-Gm-Message-State: AOAM53082yeoK1naol+96Vm2E6tgLe6JZuvaODmM70KmiGyHvAppaeME EYYOZ0y6bLsDkRXnDknV9Mo= X-Google-Smtp-Source: ABdhPJy9Hem/czLyWK70h8/P2p5xPoo2I4kiQ4m3loTu8MSzwRx11dA9W5VozMSHhvYoEyoRhDjHXg== X-Received: by 2002:a63:190b:: with SMTP id z11mr1452922pgl.314.1619063672973; Wed, 21 Apr 2021 20:54:32 -0700 (PDT) Received: from ?IPv6:2601:647:4000:d7:bce0:5b8f:12:4649? ([2601:647:4000:d7:bce0:5b8f:12:4649]) by smtp.gmail.com with ESMTPSA id ch21sm3386255pjb.8.2021.04.21.20.54.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 21 Apr 2021 20:54:32 -0700 (PDT) Subject: Re: [PATCH v7 3/5] blk-mq: Fix races between iterating over requests and freeing requests To: Ming Lei Cc: Jens Axboe , linux-block@vger.kernel.org, Christoph Hellwig , Daniel Wagner , Khazhismel Kumykov , Shin'ichiro Kawasaki , "Martin K . Petersen" , Hannes Reinecke , Johannes Thumshirn , John Garry References: <20210421000235.2028-1-bvanassche@acm.org> <20210421000235.2028-4-bvanassche@acm.org> From: Bart Van Assche Message-ID: Date: Wed, 21 Apr 2021 20:54:30 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 4/21/21 8:15 PM, Ming Lei wrote: > On Tue, Apr 20, 2021 at 05:02:33PM -0700, Bart Van Assche wrote: >> +static bool bt_tags_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data) >> +{ >> + struct bt_tags_iter_data *iter_data = data; >> + struct blk_mq_tags *tags = iter_data->tags; >> + bool res; >> + >> + if (iter_data->flags & BT_TAG_ITER_MAY_SLEEP) { >> + down_read(&tags->iter_rwsem); >> + res = __bt_tags_iter(bitmap, bitnr, data); >> + up_read(&tags->iter_rwsem); >> + } else { >> + rcu_read_lock(); >> + res = __bt_tags_iter(bitmap, bitnr, data); >> + rcu_read_unlock(); >> + } >> + >> + return res; >> +} > > Holding one rwsem or rcu read lock won't avoid the issue completely > because request may be completed remotely in iter_data->fn(), such as > nbd_clear_req(), nvme_cancel_request(), complete_all_cmds_iter(), > mtip_no_dev_cleanup(), because blk_mq_complete_request() may complete > request in softirq, remote IPI, even wq, and the request is still > referenced in these contexts after bt_tags_iter() returns. The rwsem and RCU read lock are used to serialize iterating over requests against blk_mq_sched_free_requests() calls. I don't think it matters for this patch from which context requests are freed. Bart.