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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 C8C13C3A589 for ; Tue, 20 Aug 2019 21:21:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9782722DD6 for ; Tue, 20 Aug 2019 21:21:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729887AbfHTVVO (ORCPT ); Tue, 20 Aug 2019 17:21:14 -0400 Received: from mail-pf1-f196.google.com ([209.85.210.196]:41050 "EHLO mail-pf1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728283AbfHTVVN (ORCPT ); Tue, 20 Aug 2019 17:21:13 -0400 Received: by mail-pf1-f196.google.com with SMTP id 196so4129453pfz.8 for ; Tue, 20 Aug 2019 14:21:13 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:subject:to:cc:references:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=dud9yN/yGcd36s8g6IFmHXpjoH6Dc2KsLywQjwuNLgE=; b=X+kX5H/sDLqNsrnVWJZoU2txMKuwBFoB9/gsy7Pjf5t2ErIrbyhfNTMkwF1c7+N4pp TZSwpIl85/+Q6act3VEBCWT/xs+Xcoo2WrvMuwROMHYn94FaulYT1ejFqRcMJxKhZOkW DN9xg2UYTq0IvPWPOtPMJ/3iqtoVear/l2+VfbZNVcFH1Y3SIa5dIIx4FlzOZWrP9HM+ PpLXmGg/ZIR+DjjbgL6ZLTjSGaIyKm3LqJcCAiLtqOWCLR/Mjg3YtnDw+HXJUHSLeoJd GUdKrCkTvQuY5VMgNpX2+kcP5cuAoMglbekVjdty9Cp13VwFK6O/V6g2D3JntSwJkJ1F QLJg== X-Gm-Message-State: APjAAAU+lzJGjeSxbP6ozM3gVLMtIdwLPLU8wGaikUkVshH/xugfSRmB O1A7lGLSz5VZqJXijQiWhkok6S3O X-Google-Smtp-Source: APXvYqz6LI3q6jEZLTXl5LH2NZUdkN79wB/J6pzZ36Z6trE/bGfPdxc8z04zMWPA3yvyjPhgr9yGAw== X-Received: by 2002:a62:e515:: with SMTP id n21mr32569321pff.186.1566336073088; Tue, 20 Aug 2019 14:21:13 -0700 (PDT) Received: from desktop-bart.svl.corp.google.com ([2620:15c:2cd:202:4308:52a3:24b6:2c60]) by smtp.gmail.com with ESMTPSA id g2sm38998669pfq.88.2019.08.20.14.21.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 Aug 2019 14:21:11 -0700 (PDT) From: Bart Van Assche Subject: Re: [PATCH] block: don't acquire .sysfs_lock before removing mq & iosched kobjects To: Ming Lei , Jens Axboe Cc: linux-block@vger.kernel.org, Greg KH , Mike Snitzer References: <20190816135506.29253-1-ming.lei@redhat.com> Message-ID: <09092247-1623-57ff-6297-1abd9a8cc8a2@acm.org> Date: Tue, 20 Aug 2019 14:21:10 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190816135506.29253-1-ming.lei@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 8/16/19 6:55 AM, Ming Lei wrote: > @@ -567,8 +568,17 @@ int elevator_switch_mq(struct request_queue *q, > lockdep_assert_held(&q->sysfs_lock); > > if (q->elevator) { > - if (q->elevator->registered) > + if (q->elevator->registered) { > + /* > + * sysfs write is exclusively, release > + * sysfs_lock for avoiding deadlock with > + * sysfs built-in lock which is required > + * in either .show or .store path. > + */ > + mutex_unlock(&q->sysfs_lock); > elv_unregister_queue(q); > + mutex_lock(&q->sysfs_lock); > + } > ioc_clear_queue(q); > elevator_exit(q, q->elevator); > } Hi Ming, I don't like this part of the patch. Consider the following call chain: queue_attr_store() -> elv_iosched_store() -> __elevator_change() -> elevator_switch() -> elevator_switch_mq(). queue_attr_store() locks sysfs_lock to serialize sysfs attribute show and store callbacks. So the above changes unlocks sysfs_lock from inside such a callback function and hence breaks that serialization. Can you have a look at the alternative patch below? Thanks, Bart. Subject: [PATCH] block: Fix lock inversion triggered during request queue removal Call blk_mq_unregister_dev() after having deleted q->kobj. Move the kobject_uevent(q->mq_kobj, KOBJ_REMOVE) call from inside blk_mq_unregister_dev() to its caller. --- block/blk-mq-sysfs.c | 5 ++--- block/blk-sysfs.c | 19 +++---------------- block/elevator.c | 2 -- 3 files changed, 5 insertions(+), 21 deletions(-) diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c index d6e1a9bd7131..0ec968009791 100644 --- a/block/blk-mq-sysfs.c +++ b/block/blk-mq-sysfs.c @@ -270,16 +270,15 @@ void blk_mq_unregister_dev(struct device *dev, struct request_queue *q) struct blk_mq_hw_ctx *hctx; int i; - lockdep_assert_held(&q->sysfs_lock); - queue_for_each_hw_ctx(q, hctx, i) blk_mq_unregister_hctx(hctx); - kobject_uevent(q->mq_kobj, KOBJ_REMOVE); kobject_del(q->mq_kobj); kobject_put(&dev->kobj); + mutex_lock(&q->sysfs_lock); q->mq_sysfs_init_done = false; + mutex_unlock(&q->sysfs_lock); } void blk_mq_hctx_kobj_init(struct blk_mq_hw_ctx *hctx) diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 977c659dcd18..e6f8cd99aded 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -1029,31 +1029,18 @@ void blk_unregister_queue(struct gendisk *disk) if (!test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags)) return; - /* - * Since sysfs_remove_dir() prevents adding new directory entries - * before removal of existing entries starts, protect against - * concurrent elv_iosched_store() calls. - */ - mutex_lock(&q->sysfs_lock); - blk_queue_flag_clear(QUEUE_FLAG_REGISTERED, q); - /* - * Remove the sysfs attributes before unregistering the queue data - * structures that can be modified through sysfs. - */ if (queue_is_mq(q)) - blk_mq_unregister_dev(disk_to_dev(disk), q); - mutex_unlock(&q->sysfs_lock); - + kobject_uevent(q->mq_kobj, KOBJ_REMOVE); kobject_uevent(&q->kobj, KOBJ_REMOVE); kobject_del(&q->kobj); blk_trace_remove_sysfs(disk_to_dev(disk)); - mutex_lock(&q->sysfs_lock); + if (queue_is_mq(q)) + blk_mq_unregister_dev(disk_to_dev(disk), q); if (q->elevator) elv_unregister_queue(q); - mutex_unlock(&q->sysfs_lock); kobject_put(&disk_to_dev(disk)->kobj); } diff --git a/block/elevator.c b/block/elevator.c index 2f17d66d0e61..128e7cf032e1 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -495,8 +495,6 @@ int elv_register_queue(struct request_queue *q) void elv_unregister_queue(struct request_queue *q) { - lockdep_assert_held(&q->sysfs_lock); - if (q) { struct elevator_queue *e = q->elevator;