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=-7.8 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 8BA46C433DB for ; Tue, 22 Dec 2020 16:18:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5798D224DF for ; Tue, 22 Dec 2020 16:18:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727211AbgLVQRw (ORCPT ); Tue, 22 Dec 2020 11:17:52 -0500 Received: from mail-pj1-f44.google.com ([209.85.216.44]:38267 "EHLO mail-pj1-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727115AbgLVQRw (ORCPT ); Tue, 22 Dec 2020 11:17:52 -0500 Received: by mail-pj1-f44.google.com with SMTP id j13so1616101pjz.3; Tue, 22 Dec 2020 08:17:36 -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=sxn77OCGzJYARUGQUKWfpI80sEOeENkuPBT5B5kUpDE=; b=X9okfL/gcQIchLw/xycjbwrZvIhPnZST6Y1tFJWdkbhX10VOy6i8UF/09j1sAHqnEc NzT6f4y7gOl/m+TSwiwX2NI9ThakAdC0mZxX//dHaXzmGYINqOKEheIFygzlUbxWxMMT ejBDP5nRpcz6DNLv7Mr2RAMAj8pXqMTIpUoYFJW9qvS3wmPt+tUu2qp4kHMws9u4RnJc lLriTmEgUDK9AXD7+byUwrNaEGPECUDDlyivIIApCHnNY7MxSSOhYmhGZuAjFQ9A612H dXdR7yNMXoybbjk6t01xU7KbYl654IaaXFcJMFU1RMoVkb3xLu7QDFKBZNrfIfvzmNiJ g+IQ== X-Gm-Message-State: AOAM532ZB9TBy8v74z94KIDuPNxDAE5u7L40wFzAGes65p3eZNWph9Fu 3a7aMtjmTpuC1JfqupWscnk= X-Google-Smtp-Source: ABdhPJyXFh/1YdREN8IB86Dx1s4w2PX5wkZaS82gFgN2rluTbChv6WbOpjsMDsHD223TmvbczHoYrA== X-Received: by 2002:a17:90a:de95:: with SMTP id n21mr22310181pjv.62.1608653830909; Tue, 22 Dec 2020 08:17:10 -0800 (PST) Received: from [192.168.50.110] (c-73-241-217-19.hsd1.ca.comcast.net. [73.241.217.19]) by smtp.gmail.com with ESMTPSA id s1sm20645213pfb.103.2020.12.22.08.17.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 22 Dec 2020 08:17:09 -0800 (PST) Subject: Re: [RFC PATCH v2 2/2] blk-mq: Lockout tagset iter when freeing rqs To: John Garry , axboe@kernel.dk, ming.lei@redhat.com Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, hch@lst.de, hare@suse.de, ppvk@codeaurora.org, kashyap.desai@broadcom.com, linuxarm@huawei.com References: <1608203273-170555-1-git-send-email-john.garry@huawei.com> <1608203273-170555-3-git-send-email-john.garry@huawei.com> <4d2004bb-4444-7a63-7c72-1759e3037cfd@huawei.com> <31de2806-bbc1-dcc3-b9eb-ce9257420432@acm.org> From: Bart Van Assche Message-ID: <33e41110-b3b2-ac16-f131-de1679ce8238@acm.org> Date: Tue, 22 Dec 2020 08:16:59 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 12/22/20 3:15 AM, John Garry wrote: > So then we could have something like this: > > ---8<--- > >  -435,9 +444,13 @@ void blk_mq_queue_tag_busy_iter(struct request_queue > *q, busy_iter_fn *fn, >     if (!blk_mq_hw_queue_mapped(hctx)) >             continue; > > +    while (!atomic_inc_not_zero(&tags->iter_usage_counter)); > + >     if (tags->nr_reserved_tags) >         bt_for_each(hctx, tags->breserved_tags, fn, priv, true); >     bt_for_each(hctx, tags->bitmap_tags, fn, priv, false); > > +    atomic_dec(&tags->iter_usage_counter); > } > > blk_queue_exit(q); > > --->8--- > > And similar for blk_mq_tagset_busy_iter(). How about it? Are there any blk_mq_tagset_busy_iter() calls that happen from a context where the tag set can disappear while that function is in progress? Some blk_mq_tagset_busy_iter() calls happen from a context where it is not allowed to sleep but also where it is guaranteed that the tag set won't disappear, e.g. the call from inside sdk_mq_queue_rq(). How about using a mutex inside blk_mq_queue_tag_busy_iter() instead? As far as I can see all blk_mq_queue_tag_busy_iter() happen from a context where it is allowed to sleep. Thanks, Bart.