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 38114C4338F for ; Tue, 10 Aug 2021 01:49:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1246061052 for ; Tue, 10 Aug 2021 01:49:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237266AbhHJBt0 (ORCPT ); Mon, 9 Aug 2021 21:49:26 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:25654 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237262AbhHJBtZ (ORCPT ); Mon, 9 Aug 2021 21:49:25 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1628560144; 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=G/dSgq/cGf57vOSvcWuPjjmCIcASPDhZxQFXSenWC5Q=; b=M5LuSdqsoErJI2to74Qs5HCx60v9ux0TeahLnL4w+3ZTqHgpLrYhhxl/GIhDaWxND44XJr 5BHZAy9u7KwDCPth6VaJgew+HjBsN2z0UwO7vQ3Gc6GSnpX6gWYOfEQLpXgi8V5LGmR8CI T8myyXRub3CEZ07hCLsMs2RIVIigQlI= 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-594-y01V_X30N12RlviB-2aszw-1; Mon, 09 Aug 2021 21:49:01 -0400 X-MC-Unique: y01V_X30N12RlviB-2aszw-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 AFB5787146F; Tue, 10 Aug 2021 01:48:59 +0000 (UTC) Received: from T590 (ovpn-13-190.pek2.redhat.com [10.72.13.190]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B73C210016FB; Tue, 10 Aug 2021 01:48:51 +0000 (UTC) Date: Tue, 10 Aug 2021 09:48:46 +0800 From: Ming Lei To: "yukuai (C)" 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> <47e5faa8-f8e5-86db-05a1-559e3b3c04b5@huawei.com> <3adf6183-bf40-10cd-b8ed-552120028ca3@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3adf6183-bf40-10cd-b8ed-552120028ca3@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 10:04:32PM +0800, yukuai (C) wrote: > On 2021/08/09 17:46, Ming Lei wrote: > > On Mon, Aug 09, 2021 at 03:08:26PM +0800, yukuai (C) wrote: > > > On 2021/08/09 14:28, Ming Lei wrote: > > > > 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. > > > > > > Hi, Ming > > > > > > There are two problems here in nbd, both reported by our syzkaller. > > > > > > The first is that blk_mq_tag_to_rq() returned a freed request, which is > > > because tags->static_rq[] is freed without clearing tags->rq[]. > > > Syzkaller log shows that a reply package is sent to client without > > > the client's request package. And this patch is trying to solve this > > > problem. > > > > It is still driver's problem: > > > > ->static_rq is freed in blk_mq_free_tag_set() which is called after > > blk_cleanup_disk() returns. Once blk_cleanup_disk() returns, there > > shouldn't be any driver activity, including calling blk_mq_tag_to_rq() > > by passing one invalid tag. > > > > Hi, Ming > > I understand if static_rq is freed through blk_mq_free_tag_set(), > drivers should not use static_rq anymore. > > By the way, I was thinking about another path: > > blk_mq_update_nr_requests > if (!hctx->sched_tags) -> if this is true > ret = blk_mq_tag_update_depth(hctx, &hctx->tags, nr, false) > blk_mq_free_rqs -> static_rq is freed here > > If this path concurrent with nbd_read_stat(), nbd_read_stat() can > get a freed request by blk_mq_tag_to_rq(), since tags->lock is not > held. > > t1: nbd_read_stat t2: blk_mq_update_nr_requests > rq = blk_mq_tag_to_rq() > blk_mq_free_rqs t1 isn't supposed to happen when t2 is running. blk_mq_update_nr_requests() is only called by nbd_start_device(). nbd_start_device(): if (nbd->task_recv) return -EBUSY; ... nbd->recv_workq = alloc_workqueue() That means nbd_config_put() has been called and ->config_refs has dropped to zero, so socket has been shutdown, and ->recv_workq has been destroyed, so t1 isn't supposed to happen when t2 is running. > > By holding tags->lock, we can check that rq state is idle, and it's > ref is 0. Firstly tags->lock can't fix the race[1], secondly it should be addressed in driver. [1] https://lore.kernel.org/linux-block/20210809030927.1946162-2-yukuai3@huawei.com/T/#m6651289c5718b45a8ae8a7efc889248f8cb904a3 Thanks, Ming