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=-17.2 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=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 57D75C6369E for ; Thu, 3 Dec 2020 00:57:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EE5A3221FD for ; Thu, 3 Dec 2020 00:57:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728306AbgLCA4x (ORCPT ); Wed, 2 Dec 2020 19:56:53 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:25890 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727847AbgLCA4w (ORCPT ); Wed, 2 Dec 2020 19:56:52 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606956926; 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=u6jjHOQzTA8Sd3JCKVBROP9JIJ2GaIP3pAhLVVnfILY=; b=KcQI2Id6CVi7stZ8gxOkZlpWM+Mnt2/NNmPUuL6S439jWIKmidmlOMqWYqkYXm3LvTN+V/ WEktNZEV6rmVWAB6FaR9avU6Vq8kENCsk6FXEw0nNIlzMuh7LTyGOlxbzR78lHnnFA88Bd cx/rBRuXk2stGLsHOsd6RqbyeI6gckE= 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-16-aAsKkszZP4K7l5CGxIlTdA-1; Wed, 02 Dec 2020 19:55:22 -0500 X-MC-Unique: aAsKkszZP4K7l5CGxIlTdA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9272B107B45E; Thu, 3 Dec 2020 00:55:20 +0000 (UTC) Received: from T590 (ovpn-12-87.pek2.redhat.com [10.72.12.87]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9ED7F60855; Thu, 3 Dec 2020 00:55:10 +0000 (UTC) Date: Thu, 3 Dec 2020 08:55:05 +0800 From: Ming Lei To: John Garry Cc: axboe@kernel.dk, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, hch@lst.de, hare@suse.de, ppvk@codeaurora.org, bvanassche@acm.org, kashyap.desai@broadcom.com Subject: Re: [RFC PATCH] blk-mq: Clean up references when freeing rqs Message-ID: <20201203005505.GB540033@T590> References: <1606827738-238646-1-git-send-email-john.garry@huawei.com> <20201202033134.GD494805@T590> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Wed, Dec 02, 2020 at 11:18:31AM +0000, John Garry wrote: > On 02/12/2020 03:31, Ming Lei wrote: > > On Tue, Dec 01, 2020 at 09:02:18PM +0800, John Garry wrote: > > > It has been reported many times that a use-after-free can be intermittently > > > found when iterating busy requests: > > > > > > - https://lore.kernel.org/linux-block/8376443a-ec1b-0cef-8244-ed584b96fa96@huawei.com/ > > > - https://lore.kernel.org/linux-block/5c3ac5af-ed81-11e4-fee3-f92175f14daf@acm.org/T/#m6c1ac11540522716f645d004e2a5a13c9f218908 > > > - https://lore.kernel.org/linux-block/04e2f9e8-79fa-f1cb-ab23-4a15bf3f64cc@kernel.dk/ > > > > > > The issue is that when we switch scheduler or change queue nr_requests, > > > the driver tagset may keep references to the stale requests. > > > > > > As a solution, clean up any references to those requests in the driver > > > tagset when freeing. This is done with a cmpxchg to make safe any race > > > with setting the driver tagset request from another queue. > > > > > > Signed-off-by: John Garry > > > -- > > > Set as RFC as I need to test more. And not sure on solution method, as > > > Bart had another idea. > > > > > > diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c > > > index d1eafe2c045c..9b042c7036b3 100644 > > > --- a/block/blk-mq-sched.c > > > +++ b/block/blk-mq-sched.c > > > @@ -621,7 +621,7 @@ void blk_mq_sched_free_requests(struct request_queue *q) > > > queue_for_each_hw_ctx(q, hctx, i) { > > > if (hctx->sched_tags) > > > - blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i); > > > + blk_mq_free_rqs_ext(q->tag_set, hctx->sched_tags, i, hctx->tags); > > > } > > > } > > > diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c > > > index 9c92053e704d..562db72e7d79 100644 > > > --- a/block/blk-mq-tag.c > > > +++ b/block/blk-mq-tag.c > > > @@ -576,7 +576,7 @@ int blk_mq_tag_update_depth(struct blk_mq_hw_ctx *hctx, > > > return -ENOMEM; > > > } > > > - blk_mq_free_rqs(set, *tagsptr, hctx->queue_num); > > > + blk_mq_free_rqs_ext(set, *tagsptr, hctx->queue_num, hctx->tags); > > > blk_mq_free_rq_map(*tagsptr, flags); > > > *tagsptr = new; > > > } else { > > > diff --git a/block/blk-mq.c b/block/blk-mq.c > > > index 55bcee5dc032..f3aad695cd25 100644 > > > --- a/block/blk-mq.c > > > +++ b/block/blk-mq.c > > > @@ -2271,8 +2271,8 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio) > > > return BLK_QC_T_NONE; > > > } > > > -void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, > > > - unsigned int hctx_idx) > > > +void blk_mq_free_rqs_ext(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, > > > + unsigned int hctx_idx, struct blk_mq_tags *references) > > > { > > > struct page *page; > > > @@ -2281,10 +2281,13 @@ 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); > > > + for (j = 0; references && j < references->nr_tags; j++) > > > + cmpxchg(&references->rqs[j], rq, 0); > > > > Seems you didn't address the comment in the following link: > > > > https://lore.kernel.org/linux-block/10331543-9e45-ae63-8cdb-17e5a2a3b7ef@huawei.com/ > > > > The request to be freed may still be refered in another path, such as blk_mq_queue_tag_busy_iter > > or blk_mq_tagset_busy_iter(), and cmpxchg() doesn't drain/wait for other refers. > > > > Hi Ming, > > Yeah, so I said that was another problem which you mentioned there, which > I'm not addressing, but I don't think that I'm making thing worse here. The thing is that this patch does not fix the issue completely. > > So AFAICS, the blk-mq/sched code doesn't wait for any "readers" to be > finished, such as those running blk_mq_queue_tag_busy_iter or > blk_mq_tagset_busy_iter() in another context. > > So how about the idea of introducing some synchronization primitive, such as > semaphore, which those "readers" must grab and release at start and end (of > iter), to ensure the requests are not freed during the iteration? It looks good, however devil is in details, please make into patch for review. thanks, Ming