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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 B1B87C433E0 for ; Sat, 6 Mar 2021 18:14:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6F9D664FE9 for ; Sat, 6 Mar 2021 18:14:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231183AbhCFSNk (ORCPT ); Sat, 6 Mar 2021 13:13:40 -0500 Received: from mail-pj1-f50.google.com ([209.85.216.50]:35406 "EHLO mail-pj1-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230346AbhCFSNQ (ORCPT ); Sat, 6 Mar 2021 13:13:16 -0500 Received: by mail-pj1-f50.google.com with SMTP id ga23-20020a17090b0397b02900c0b81bbcd4so856742pjb.0; Sat, 06 Mar 2021 10:13:16 -0800 (PST) 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=JjqFOEuF/irQ0wQ7BMz3JdcfoaUBCUP+26117l0UxWo=; b=EdedKj+kyaRs843I9nODkBSga3MwcdRMamAxpSIMSN35msixygy0u4/32hRqTWI7Lq 6dn3ym71yN6XAiJeaYEx9WklIU/i184IoLROLQa/tKIxhmTRfw78IQxnlL8z+b68uDgC f5eRXaSd25zft5OU7UgV/CsG8e6EUBhbF4lpDQqS9ThoWPrqrbXa0GrnM9UfGZs3+QcC PIjlKuGYWcrdcdpS0k22lEivLvBCLKuefi9SXnJL1SGnnOO/Joo+pT8Bw1IWkt41B+py Zi/wIt65M+d+YFXJ50BqoJA3ywnQvkxVvmScnf7QtdzsP5ZtypVOa88NrGZAN4zJbyxg EUlw== X-Gm-Message-State: AOAM530tvjNVWnyCbtUOoEfzzJqogJyG3k99TMGDO21Nf0eZWaoLQRLh Ad0G0K6/k0W6QR/D/cEl+6MmFPFD6OQ= X-Google-Smtp-Source: ABdhPJyYbm/S/JfNG4pysZBmANmlNFNJ6xx2wpr3076gFmpnSxxnR4XY0YOf2ghPIv9NyxQYSu57IQ== X-Received: by 2002:a17:90a:20c:: with SMTP id c12mr16287332pjc.224.1615054395496; Sat, 06 Mar 2021 10:13:15 -0800 (PST) Received: from ?IPv6:2601:647:4000:d7:9183:7829:b654:e538? ([2601:647:4000:d7:9183:7829:b654:e538]) by smtp.gmail.com with ESMTPSA id q9sm5646141pgs.28.2021.03.06.10.13.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 06 Mar 2021 10:13:14 -0800 (PST) Subject: Re: [RFC PATCH v3 1/3] blk-mq: Clean up references to old requests when freeing rqs To: John Garry , hare@suse.de, ming.lei@redhat.com, axboe@kernel.dk, hch@lst.de Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, pragalla@codeaurora.org, kashyap.desai@broadcom.com, yuyufen@huawei.com References: <1614957294-188540-1-git-send-email-john.garry@huawei.com> <1614957294-188540-2-git-send-email-john.garry@huawei.com> From: Bart Van Assche Message-ID: Date: Sat, 6 Mar 2021 10:13:11 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <1614957294-188540-2-git-send-email-john.garry@huawei.com> 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 3/5/21 7:14 AM, John Garry wrote: > @@ -2296,10 +2296,14 @@ void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, > > for (i = 0; i < tags->nr_tags; i++) { > struct request *rq = tags->static_rqs[i]; > + int j; > > if (!rq) > continue; > set->ops->exit_request(set, rq, hctx_idx); > + /* clean up any references which occur in @ref_tags */ > + for (j = 0; ref_tags && j < ref_tags->nr_tags; j++) > + cmpxchg(&ref_tags->rqs[j], rq, 0); > tags->static_rqs[i] = NULL; > } > } What prevents blk_mq_tagset_busy_iter() from reading hctx->tags[...] before the cmpxcg() call and dereferencing it after blk_mq_free_rqs() has called __free_pages()? Thanks, Bart.