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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 3128EC4360F for ; Thu, 4 Apr 2019 21:30:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 07EFD2171F for ; Thu, 4 Apr 2019 21:30:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729865AbfDDVaY (ORCPT ); Thu, 4 Apr 2019 17:30:24 -0400 Received: from mail-pf1-f196.google.com ([209.85.210.196]:38751 "EHLO mail-pf1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729831AbfDDVaX (ORCPT ); Thu, 4 Apr 2019 17:30:23 -0400 Received: by mail-pf1-f196.google.com with SMTP id 10so2016318pfo.5; Thu, 04 Apr 2019 14:30:23 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:message-id:subject:from:to:cc:date:in-reply-to :references:mime-version:content-transfer-encoding; bh=YL7c7IPYFwI3LDsFYU0x4w4N8nYF2KkSIbJSux/1CMg=; b=RHJYjoJIeGINQsAHTzx72194MFRA+tUpEFBzxmBURTqTB9GUEsCiLarcvOQ45ip95l KSNbrqicJUR18isZOmqwunl/ABrEw7wNEb0F6RsL+XZioF03e2s5gvrvySOfHy9FqTqZ FByKKlCsGjUOgPqLruDxJIrfk2SO38uF8kJuvv7DXomLchiP2Xlssi/+wIrGiumT42NX EgxyFt4XXXe8IsVa+nszbnEayf+qbYgDCrOh0z+cMhVbQ8vo+RNXlsdtyqnyGxsYWHmh XZo5fUwZg+V0I6bruQDd9eXagx94eTKYyE8W5PjKVZ418IOiWrV72dwNTrcNCFLckv2f 9NNA== X-Gm-Message-State: APjAAAUhdzjZS2rxFQ4BzHnViMFqD6mYYNPlREafJAlU0knfCJ1YhyjX 1+tcEr3l2GcRSk/N9pI6HnM= X-Google-Smtp-Source: APXvYqym55lLD+cmt9TDzsa1jt9SdNSu/fzV3Fx3Jmm00QYNM4Tpes0m9y7auQr+6yfiEL1LIDbraA== X-Received: by 2002:a62:b612:: with SMTP id j18mr8499195pff.124.1554413422907; Thu, 04 Apr 2019 14:30:22 -0700 (PDT) Received: from ?IPv6:2620:15c:2cd:203:5cdc:422c:7b28:ebb5? ([2620:15c:2cd:203:5cdc:422c:7b28:ebb5]) by smtp.gmail.com with ESMTPSA id v20sm30044801pfn.116.2019.04.04.14.30.21 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 04 Apr 2019 14:30:22 -0700 (PDT) Message-ID: <1554413420.118779.260.camel@acm.org> Subject: Re: [PATCH V4 1/7] blk-mq: grab .q_usage_counter when queuing request from plug code path From: Bart Van Assche To: Ming Lei , Jens Axboe Cc: linux-block@vger.kernel.org, Dongli Zhang , James Smart , Bart Van Assche , linux-scsi@vger.kernel.org, "Martin K . Petersen" , Christoph Hellwig , "James E . J . Bottomley" , jianchao wang Date: Thu, 04 Apr 2019 14:30:20 -0700 In-Reply-To: <20190404084320.24681-2-ming.lei@redhat.com> References: <20190404084320.24681-1-ming.lei@redhat.com> <20190404084320.24681-2-ming.lei@redhat.com> Content-Type: text/plain; charset="UTF-7" X-Mailer: Evolution 3.26.2-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, 2019-04-04 at 16:43 +-0800, Ming Lei wrote: +AD4 Just like aio/io+AF8-uring, we need to grab 2 refcount for queuing one +AD4 request, one is for submission, another is for completion. +AD4 +AD4 If the request isn't queued from plug code path, the refcount grabbed +AD4 in generic+AF8-make+AF8-request() serves for submission. In theroy, this +AD4 refcount should have been released after the sumission(async run queue) +AD4 is done. blk+AF8-freeze+AF8-queue() works with blk+AF8-sync+AF8-queue() together +AD4 for avoiding race between cleanup queue and IO submission, given async +AD4 run queue activities are canceled because hctx-+AD4-run+AF8-work is scheduled with +AD4 the refcount held, so it is fine to not hold the refcount when +AD4 running the run queue work function for dispatch IO. +AD4 +AD4 However, if request is staggered into plug list, and finally queued +AD4 from plug code path, the refcount in submission side is actually missed. +AD4 And we may start to run queue after queue is removed because the queue's +AD4 kobject refcount isn't guaranteed to be grabbed in flushing plug list +AD4 context, then kernel oops is triggered, see the following race: +AD4 +AD4 blk+AF8-mq+AF8-flush+AF8-plug+AF8-list(): +AD4 blk+AF8-mq+AF8-sched+AF8-insert+AF8-requests() +AD4 insert requests to sw queue or scheduler queue +AD4 blk+AF8-mq+AF8-run+AF8-hw+AF8-queue +AD4 +AD4 Because of concurrent run queue, all requests inserted above may be +AD4 completed before calling the above blk+AF8-mq+AF8-run+AF8-hw+AF8-queue. Then queue can +AD4 be freed during the above blk+AF8-mq+AF8-run+AF8-hw+AF8-queue(). +AD4 +AD4 Fixes the issue by grab .q+AF8-usage+AF8-counter before calling +AD4 blk+AF8-mq+AF8-sched+AF8-insert+AF8-requests() in blk+AF8-mq+AF8-flush+AF8-plug+AF8-list(). This way is +AD4 safe because the queue is absolutely alive before inserting request. Reviewed-by: Bart Van Assche +ADw-bvanassche+AEA-acm.org+AD4-