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=-18.8 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, USER_AGENT_GIT 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 C6A57C43333 for ; Mon, 1 Mar 2021 19:48:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8FF4E64D8F for ; Mon, 1 Mar 2021 19:48:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242118AbhCATsH (ORCPT ); Mon, 1 Mar 2021 14:48:07 -0500 Received: from mail.kernel.org ([198.145.29.99]:54010 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235541AbhCAQz3 (ORCPT ); Mon, 1 Mar 2021 11:55:29 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id B2BBC64F64; Mon, 1 Mar 2021 16:35:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1614616542; bh=6zyezWTTjuoD2AKf98TGmXgyShjSqOTOrLzonJpdurA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=id0oUmfNikPJVHbb9GP3gd4MGRMexqpCrjwkYDY7gkm8qM6e+mh66mwDOEnadC0dy vWQSoLAT2TMX5BFVgaec6YRwWe1wYOAdmroKqPIpMr+9Z2LNbu94cBoNUQvazdDH4F KObx2w6yrPW3+wn6UXG+BCpq5nGESx3SkSaC934A= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Christoph Hellwig , Hannes Reinecke , Mike Snitzer , Bart Van Assche , Ming Lei , Jens Axboe , Jack Wang Subject: [PATCH 4.19 011/247] block: dont release queues sysfs lock during switching elevator Date: Mon, 1 Mar 2021 17:10:31 +0100 Message-Id: <20210301161032.233407922@linuxfoundation.org> X-Mailer: git-send-email 2.30.1 In-Reply-To: <20210301161031.684018251@linuxfoundation.org> References: <20210301161031.684018251@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Ming Lei commit b89f625e28d44552083f43752f62d8621ded0a04 upstream. cecf5d87ff20 ("block: split .sysfs_lock into two locks") starts to release & acquire sysfs_lock before registering/un-registering elevator queue during switching elevator for avoiding potential deadlock from showing & storing 'queue/iosched' attributes and removing elevator's kobject. Turns out there isn't such deadlock because 'q->sysfs_lock' isn't required in .show & .store of queue/iosched's attributes, and just elevator's sysfs lock is acquired in elv_iosched_store() and elv_iosched_show(). So it is safe to hold queue's sysfs lock when registering/un-registering elevator queue. The biggest issue is that commit cecf5d87ff20 assumes that concurrent write on 'queue/scheduler' can't happen. However, this assumption isn't true, because kernfs_fop_write() only guarantees that concurrent write aren't called on the same open file, but the write could be from different open on the file. So we can't release & re-acquire queue's sysfs lock during switching elevator, otherwise use-after-free on elevator could be triggered. Fixes the issue by not releasing queue's sysfs lock during switching elevator. Fixes: cecf5d87ff20 ("block: split .sysfs_lock into two locks") Cc: Christoph Hellwig Cc: Hannes Reinecke Cc: Greg KH Cc: Mike Snitzer Reviewed-by: Bart Van Assche Signed-off-by: Ming Lei Signed-off-by: Jens Axboe (jwang: adjust ctx for 4.19) Signed-off-by: Jack Wang Signed-off-by: Greg Kroah-Hartman --- block/blk-sysfs.c | 3 ++- block/elevator.c | 31 +------------------------------ 2 files changed, 3 insertions(+), 31 deletions(-) --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -933,6 +933,7 @@ int blk_register_queue(struct gendisk *d blk_mq_debugfs_register(q); } + mutex_lock(&q->sysfs_lock); /* * The flag of QUEUE_FLAG_REGISTERED isn't set yet, so elevator * switch won't happen at all. @@ -940,6 +941,7 @@ int blk_register_queue(struct gendisk *d if (q->request_fn || (q->mq_ops && q->elevator)) { ret = elv_register_queue(q, false); if (ret) { + mutex_unlock(&q->sysfs_lock); mutex_unlock(&q->sysfs_dir_lock); kobject_del(&q->kobj); blk_trace_remove_sysfs(dev); @@ -949,7 +951,6 @@ int blk_register_queue(struct gendisk *d has_elevator = true; } - mutex_lock(&q->sysfs_lock); blk_queue_flag_set(QUEUE_FLAG_REGISTERED, q); wbt_enable_default(q); blk_throtl_register_queue(q); --- a/block/elevator.c +++ b/block/elevator.c @@ -856,11 +856,9 @@ int elv_register_queue(struct request_qu if (uevent) kobject_uevent(&e->kobj, KOBJ_ADD); - mutex_lock(&q->sysfs_lock); e->registered = 1; if (!e->uses_mq && e->type->ops.sq.elevator_registered_fn) e->type->ops.sq.elevator_registered_fn(q); - mutex_unlock(&q->sysfs_lock); } return error; } @@ -878,11 +876,9 @@ void elv_unregister_queue(struct request kobject_uevent(&e->kobj, KOBJ_REMOVE); kobject_del(&e->kobj); - mutex_lock(&q->sysfs_lock); e->registered = 0; /* Re-enable throttling in case elevator disabled it */ wbt_enable_default(q); - mutex_unlock(&q->sysfs_lock); } } @@ -953,32 +949,11 @@ int elevator_switch_mq(struct request_qu lockdep_assert_held(&q->sysfs_lock); if (q->elevator) { - if (q->elevator->registered) { - mutex_unlock(&q->sysfs_lock); - - /* - * Concurrent elevator switch can't happen becasue - * sysfs write is always exclusively on same file. - * - * Also the elevator queue won't be freed after - * sysfs_lock is released becasue kobject_del() in - * blk_unregister_queue() waits for completion of - * .store & .show on its attributes. - */ + if (q->elevator->registered) elv_unregister_queue(q); - mutex_lock(&q->sysfs_lock); - } ioc_clear_queue(q); elevator_exit(q, q->elevator); - - /* - * sysfs_lock may be dropped, so re-check if queue is - * unregistered. If yes, don't switch to new elevator - * any more - */ - if (!blk_queue_registered(q)) - return 0; } ret = blk_mq_init_sched(q, new_e); @@ -986,11 +961,7 @@ int elevator_switch_mq(struct request_qu goto out; if (new_e) { - mutex_unlock(&q->sysfs_lock); - ret = elv_register_queue(q, true); - - mutex_lock(&q->sysfs_lock); if (ret) { elevator_exit(q, q->elevator); goto out;