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=-16.0 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 6958CC433DB for ; Tue, 16 Mar 2021 16:36:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3CFFD6510B for ; Tue, 16 Mar 2021 16:36:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238727AbhCPQgH (ORCPT ); Tue, 16 Mar 2021 12:36:07 -0400 Received: from mx4.veeam.com ([104.41.138.86]:59098 "EHLO mx4.veeam.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237871AbhCPQf6 (ORCPT ); Tue, 16 Mar 2021 12:35:58 -0400 Received: from mail.veeam.com (prgmbx01.amust.local [172.24.0.171]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx4.veeam.com (Postfix) with ESMTPS id 3FCF38A77C; Tue, 16 Mar 2021 19:35:53 +0300 (MSK) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=veeam.com; s=mx4; t=1615912553; bh=F1gKLL7wk3iE1vLbPnTkUW3slRzh6GWWwMLJyS5YH1U=; h=Date:From:To:CC:Subject:References:In-Reply-To:From; b=LgzU5IuRT4MU2/aszmA5F9lbIBFZyR0JP9db5s+sCQFZiTjb45y6KnOJxlsOfzgGF 2TgpDyaufoHsv+9icTxQL+xZ6vLqIKVJ3pB4tYjq5umA9JBEcWgrbih71QTueezVpN YP/fey343S+4gT4Xc9pWcLfTWJlQBacMoU6aItoE= Received: from veeam.com (172.24.14.5) by prgmbx01.amust.local (172.24.0.171) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.721.2; Tue, 16 Mar 2021 17:35:50 +0100 Date: Tue, 16 Mar 2021 19:35:44 +0300 From: Sergei Shtepa To: Ming Lei CC: Christoph Hellwig , Mike Snitzer , Alasdair Kergon , Hannes Reinecke , Jens Axboe , "dm-devel@redhat.com" , "linux-block@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-api@vger.kernel.org" , Pavel Tide Subject: Re: [PATCH v7 2/3] block: add bdev_interposer Message-ID: <20210316163544.GA31272@veeam.com> References: <1615563895-28565-1-git-send-email-sergei.shtepa@veeam.com> <1615563895-28565-3-git-send-email-sergei.shtepa@veeam.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline In-Reply-To: X-Originating-IP: [172.24.14.5] X-ClientProxiedBy: prgmbx02.amust.local (172.24.0.172) To prgmbx01.amust.local (172.24.0.171) X-EsetResult: clean, is OK X-EsetId: 37303A29D2A50B586D756B X-Veeam-MMEX: True Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org The 03/16/2021 11:09, Ming Lei wrote: > On Fri, Mar 12, 2021 at 06:44:54PM +0300, Sergei Shtepa wrote: > > bdev_interposer allows to redirect bio requests to another devices. > > > > Signed-off-by: Sergei Shtepa > > --- > > block/bio.c | 2 ++ > > block/blk-core.c | 57 +++++++++++++++++++++++++++++++++++++++ > > block/genhd.c | 54 +++++++++++++++++++++++++++++++++++++ > > include/linux/blk_types.h | 3 +++ > > include/linux/blkdev.h | 9 +++++++ > > 5 files changed, 125 insertions(+) > > > > diff --git a/block/bio.c b/block/bio.c > > index a1c4d2900c7a..0bfbf06475ee 100644 > > --- a/block/bio.c > > +++ b/block/bio.c > > @@ -640,6 +640,8 @@ void __bio_clone_fast(struct bio *bio, struct bio *bio_src) > > bio_set_flag(bio, BIO_THROTTLED); > > if (bio_flagged(bio_src, BIO_REMAPPED)) > > bio_set_flag(bio, BIO_REMAPPED); > > + if (bio_flagged(bio_src, BIO_INTERPOSED)) > > + bio_set_flag(bio, BIO_INTERPOSED); > > bio->bi_opf = bio_src->bi_opf; > > bio->bi_ioprio = bio_src->bi_ioprio; > > bio->bi_write_hint = bio_src->bi_write_hint; > > diff --git a/block/blk-core.c b/block/blk-core.c > > index fc60ff208497..da1abc4c27a9 100644 > > --- a/block/blk-core.c > > +++ b/block/blk-core.c > > @@ -1018,6 +1018,55 @@ static blk_qc_t __submit_bio_noacct_mq(struct bio *bio) > > return ret; > > } > > > > +static noinline blk_qc_t submit_bio_interposed(struct bio *bio) > > +{ > > + blk_qc_t ret = BLK_QC_T_NONE; > > + struct bio_list bio_list[2] = { }; > > + struct gendisk *orig_disk; > > + > > + if (current->bio_list) { > > + bio_list_add(¤t->bio_list[0], bio); > > + return BLK_QC_T_NONE; > > + } > > + > > + orig_disk = bio->bi_bdev->bd_disk; > > + if (unlikely(bio_queue_enter(bio))) > > + return BLK_QC_T_NONE; > > + > > + current->bio_list = bio_list; > > + > > + do { > > + struct block_device *interposer = bio->bi_bdev->bd_interposer; > > + > > + if (unlikely(!interposer)) { > > + /* interposer was removed */ > > + bio_list_add(¤t->bio_list[0], bio); > > + break; > > + } > > + /* assign bio to interposer device */ > > + bio_set_dev(bio, interposer); > > + bio_set_flag(bio, BIO_INTERPOSED); > > + > > + if (!submit_bio_checks(bio)) > > + break; > > + /* > > + * Because the current->bio_list is initialized, > > + * the submit_bio callback will always return BLK_QC_T_NONE. > > + */ > > + interposer->bd_disk->fops->submit_bio(bio); > > Given original request queue may become live when calling attach() and > detach(), see below comment. bdev_interposer_detach() may be run > when running ->submit_bio(), meantime the interposer device is > gone during the period, then kernel oops. I think that since the bio_queue_enter() function was called, q->q_usage_counter will not allow the critical code in the attach/detach functions to be executed, which is located between the blk_freeze_queue and blk_unfreeze_queue calls. Please correct me if I'm wrong. > > > + } while (false); > > + > > + current->bio_list = NULL; > > + > > + blk_queue_exit(orig_disk->queue); > > + > > + /* Resubmit remaining bios */ > > + while ((bio = bio_list_pop(&bio_list[0]))) > > + ret = submit_bio_noacct(bio); > > + > > + return ret; > > +} > > + > > /** > > * submit_bio_noacct - re-submit a bio to the block device layer for I/O > > * @bio: The bio describing the location in memory and on the device. > > @@ -1029,6 +1078,14 @@ static blk_qc_t __submit_bio_noacct_mq(struct bio *bio) > > */ > > blk_qc_t submit_bio_noacct(struct bio *bio) > > { > > + /* > > + * Checking the BIO_INTERPOSED flag is necessary so that the bio > > + * created by the bdev_interposer do not get to it for processing. > > + */ > > + if (bdev_has_interposer(bio->bi_bdev) && > > + !bio_flagged(bio, BIO_INTERPOSED)) > > + return submit_bio_interposed(bio); > > + > > if (!submit_bio_checks(bio)) > > return BLK_QC_T_NONE; > > > > diff --git a/block/genhd.c b/block/genhd.c > > index c55e8f0fced1..c840ecffea68 100644 > > --- a/block/genhd.c > > +++ b/block/genhd.c > > @@ -30,6 +30,11 @@ > > static struct kobject *block_depr; > > > > DECLARE_RWSEM(bdev_lookup_sem); > > +/* > > + * Prevents different block-layer interposers from attaching or detaching > > + * to the block device at the same time. > > + */ > > +static DEFINE_MUTEX(bdev_interposer_attach_lock); > > > > /* for extended dynamic devt allocation, currently only one major is used */ > > #define NR_EXT_DEVT (1 << MINORBITS) > > @@ -1940,3 +1945,52 @@ static void disk_release_events(struct gendisk *disk) > > WARN_ON_ONCE(disk->ev && disk->ev->block != 1); > > kfree(disk->ev); > > } > > + > > +int bdev_interposer_attach(struct block_device *original, > > + struct block_device *interposer) > > +{ > > + int ret = 0; > > + > > + if (WARN_ON(((!original) || (!interposer)))) > > + return -EINVAL; > > + /* > > + * interposer should be simple, no a multi-queue device > > + */ > > + if (!interposer->bd_disk->fops->submit_bio) > > + return -EINVAL; > > + > > + if (WARN_ON(!blk_mq_is_queue_frozen(original->bd_disk->queue))) > > + return -EPERM; > > The original request queue may become live now... Yes. I will remove the blk_mq_is_queue_frozen() function and use a different approach. > > > + > > + mutex_lock(&bdev_interposer_attach_lock); > > + > > + if (bdev_has_interposer(original)) > > + ret = -EBUSY; > > + else { > > + original->bd_interposer = bdgrab(interposer); > > + if (!original->bd_interposer) > > + ret = -ENODEV; > > + } > > + > > + mutex_unlock(&bdev_interposer_attach_lock); > > + > > + return ret; > > +} > > +EXPORT_SYMBOL_GPL(bdev_interposer_attach); > > + > > +void bdev_interposer_detach(struct block_device *original) > > +{ > > + if (WARN_ON(!original)) > > + return; > > + > > + if (WARN_ON(!blk_mq_is_queue_frozen(original->bd_disk->queue))) > > + return; > > The original request queue may become live now... > > > -- > Ming > -- Sergei Shtepa Veeam Software developer.