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 584ECC433B4 for ; Sun, 25 Apr 2021 21:01:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3198D6127C for ; Sun, 25 Apr 2021 21:01:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231209AbhDYVBy (ORCPT ); Sun, 25 Apr 2021 17:01:54 -0400 Received: from mail-pf1-f175.google.com ([209.85.210.175]:41545 "EHLO mail-pf1-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231197AbhDYVBx (ORCPT ); Sun, 25 Apr 2021 17:01:53 -0400 Received: by mail-pf1-f175.google.com with SMTP id w6so23082952pfc.8; Sun, 25 Apr 2021 14:01:13 -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=YIVdBwNyYUYTkQn4HptAspu70HypxovaJAxGVFKezc4=; b=dTxMI6CwYKChg4kEc09oIpXKLeDACxvS7mNofbYPeHbp79DUFwqM//q3Z9tLDYFYal nO63oXAnSW9o3YoPtykLHr82AXaUsTeYwjnaCjGbGNy4IfNsQxwNOtvmK8uJoDGFjjFa JPwjFR+ectc1V0cv0jMSUokzwCIBM1NJCxgFmBOJWelHMJea0P0/rQFaM/fH62ozxJEF 9uhHbMLYrLTdPJSDfOEHEvMiZBRq3b2hpwphJROlqcxYNlOPHfqISY5xl62VNtbC2O4f EAZA7/7PC7wfIwsIitWomtNOtv883VCXIsksETvKa6la64LY/bsjbR2hQv+H0uJsspDo ByFw== X-Gm-Message-State: AOAM532MM4CWlbcZzRxiYzHWHHhw2S3Ntcyrv8ih+nAy0Tnxk2CT43SS h1qILcw4m7V8wXbBdB6lnLFx8skGMU0WWQ== X-Google-Smtp-Source: ABdhPJzO8vln7atkRbLhYuBEfJJsgskE9Agpu3kRhygK9gDEVjvtkpH/0pBjjdM5TSXKgFbmQcNfUw== X-Received: by 2002:a62:6101:0:b029:215:3a48:4e6e with SMTP id v1-20020a6261010000b02902153a484e6emr14617947pfb.2.1619384473131; Sun, 25 Apr 2021 14:01:13 -0700 (PDT) Received: from [192.168.3.219] (c-73-241-217-19.hsd1.ca.comcast.net. [73.241.217.19]) by smtp.gmail.com with ESMTPSA id s18sm8780933pgv.44.2021.04.25.14.01.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 25 Apr 2021 14:01:12 -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 , linux-scsi@vger.kernel.org References: <20210421000235.2028-1-bvanassche@acm.org> <20210421000235.2028-4-bvanassche@acm.org> <32a121b7-2444-ac19-420d-4961f2a18129@acm.org> <28607d75-042f-7a6a-f5d0-2ee03754917e@acm.org> From: Bart Van Assche Message-ID: <037f5a58-545c-5265-c2a2-d2e8b92168c6@acm.org> Date: Sun, 25 Apr 2021 14:01:11 -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 4/24/21 5:09 PM, Ming Lei wrote: > However, blk_mq_wait_for_tag_iter() still may return before > blk_mq_wait_for_tag_iter() is done because blk_mq_wait_for_tag_iter() > supposes all request reference is just done inside bt_tags_iter(), > especially .iter_rwsem and read rcu lock is added in bt_tags_iter(). The comment above blk_mq_wait_for_tag_iter() needs to be updated but I believe that the code is fine. Waiting for bt_tags_iter() to finish should be sufficient to fix the UAF. What matters is that the pointer read by rcu_dereference(tags->rqs[bitnr]) remains valid until the callback function has finished. I think that is guaranteed by the current implementation. Bart.