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=-16.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 84DD9C4338F for ; Mon, 9 Aug 2021 06:28:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6582D61052 for ; Mon, 9 Aug 2021 06:28:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233248AbhHIG24 (ORCPT ); Mon, 9 Aug 2021 02:28:56 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:27806 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233136AbhHIG24 (ORCPT ); Mon, 9 Aug 2021 02:28:56 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1628490515; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=XSB+qsiXiDt/LtGYRnCraHlctWmbZ6sfAQg7VcuKR9M=; b=O+0IoCJxikctsnMIl/681rfh4xxFRgC2oeTZAVPNIh6nGOy04mObUVyAqLqyyh3usy4PeP ctyqdZsO8PX0GGXdq5eJchlyS55kDOSYP0lEu1VpG6La768aAKyD03NucJOVUiCDyaZA5W DqkaejWSUiaaTx9JVccJgnT6GVbNMPM= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-120-PUrK1CkgPYeY80-D0WG0jA-1; Mon, 09 Aug 2021 02:28:33 -0400 X-MC-Unique: PUrK1CkgPYeY80-D0WG0jA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C79C48B5DC4; Mon, 9 Aug 2021 06:28:15 +0000 (UTC) Received: from T590 (ovpn-13-190.pek2.redhat.com [10.72.13.190]) by smtp.corp.redhat.com (Postfix) with ESMTPS id EE60F10013C1; Mon, 9 Aug 2021 06:28:10 +0000 (UTC) Date: Mon, 9 Aug 2021 14:28:06 +0800 From: Ming Lei To: Yu Kuai Cc: axboe@kernel.dk, josef@toxicpanda.com, bvanassche@acm.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, nbd@other.debian.org, yi.zhang@huawei.com Subject: Re: [PATCH v2 2/2] nbd: convert to use blk_mq_get_rq_by_tag() Message-ID: References: <20210809030927.1946162-1-yukuai3@huawei.com> <20210809030927.1946162-3-yukuai3@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210809030927.1946162-3-yukuai3@huawei.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Mon, Aug 09, 2021 at 11:09:27AM +0800, Yu Kuai wrote: > blk_mq_tag_to_rq() might return freed request, use > blk_mq_get_rq_by_tag() instead. > > Signed-off-by: Yu Kuai > --- > drivers/block/nbd.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c > index c38317979f74..9e56975a8eee 100644 > --- a/drivers/block/nbd.c > +++ b/drivers/block/nbd.c > @@ -713,11 +713,10 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index) > tag = nbd_handle_to_tag(handle); > hwq = blk_mq_unique_tag_to_hwq(tag); > if (hwq < nbd->tag_set.nr_hw_queues) > - req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq], > - blk_mq_unique_tag_to_tag(tag)); > - if (!req || !blk_mq_request_started(req)) { > - dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%d) %p\n", > - tag, req); > + req = blk_mq_get_rq_by_tag(nbd->tag_set.tags[hwq], > + blk_mq_unique_tag_to_tag(tag)); > + if (!req) { > + dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d\n", tag); > return ERR_PTR(-ENOENT); > } > trace_nbd_header_received(req, handle); > @@ -779,6 +778,8 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index) > } > out: > trace_nbd_payload_received(req, handle); > + if (req) > + blk_mq_put_rq_ref(req); > mutex_unlock(&cmd->lock); > return ret ? ERR_PTR(ret) : cmd; After blk_mq_put_rq_ref() returns, this request may have been freed, so the returned 'cmd' may have been freed too. As I replied in your another thread, it is driver's responsibility to cover race between normal completion and timeout/error handling, that means the caller of blk_mq_tag_to_rq need to make sure that the request represented by the passed 'tag' can't be freed. I'd suggest to understand why nbd_read_stat()/blk_mq_tag_to_rq() may return one freed request first, who frees the request and how when calling blk_mq_tag_to_rq() before figuring out solutions. Thanks, Ming