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=-16.1 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 6FC75C47096 for ; Fri, 4 Jun 2021 00:04:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4385C61406 for ; Fri, 4 Jun 2021 00:04:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229685AbhFDAGZ (ORCPT ); Thu, 3 Jun 2021 20:06:25 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:31009 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229656AbhFDAGZ (ORCPT ); Thu, 3 Jun 2021 20:06:25 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1622765079; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=d+bFfr6Xa5feZyHtnlj3QldeQG0fhNp8nYtTUpuhfSE=; b=PCtzA7HMF/wb4gJxzxgCyYT7lpJhB5ZyhRskdrrln3UKWuStIkVjTgQX7EUtRZxml7Mm+x VMruCYwugW78gaPBN8/rgt+A0ylWv9Jb3EdgDzFtilgALim+hqzRMlDYMy5pGCa6m93/pl FZLcKXzFa1WCFT729rq4gIT8OtCffSM= 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-349--J68nE8fNUq9gTmesS2l9g-1; Thu, 03 Jun 2021 20:04:36 -0400 X-MC-Unique: -J68nE8fNUq9gTmesS2l9g-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 253F3101371D; Fri, 4 Jun 2021 00:04:35 +0000 (UTC) Received: from localhost (ovpn-12-139.pek2.redhat.com [10.72.12.139]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3C92060657; Fri, 4 Jun 2021 00:04:30 +0000 (UTC) From: Ming Lei To: Jens Axboe , Christoph Hellwig Cc: linux-block@vger.kernel.org, Ming Lei , Colin Ian King , Pavel Tatashin Subject: [PATCH] block: loop: fix deadlock between open and remove Date: Fri, 4 Jun 2021 08:04:24 +0800 Message-Id: <20210604000424.189928-1-ming.lei@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Commit c76f48eb5c08 ("block: take bd_mutex around delete_partitions in del_gendisk") adds disk->part0->bd_mutex in del_gendisk(), this way causes the following AB/BA deadlock between removing loop and opening loop: 1) loop_control_ioctl(LOOP_CTL_REMOVE) - mutex_lock(&loop_ctl_mutex) - mutex_lock(&disk->part0->bd_mutex) //del_gendisk 2) open look device - mutex_lock(&disk->part0->bd_mutex) //blkdev_get_by_dev - mutex_lock(&loop_ctl_mutex) //lo_open() <- __blkdev_get Fixes the issue by not holding loop_ctl_mutex in lo_open(), and cover the protection on bdev->bd_disk->private_data via disk->part0->bd_mutex. Reported-by: Colin Ian King Fixes: c76f48eb5c08 ("block: take bd_mutex around delete_partitions in del_gendisk") Cc: Pavel Tatashin Signed-off-by: Ming Lei --- drivers/block/loop.c | 31 +++++++++++++++---------------- 1 file changed, 15 insertions(+), 16 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index d58d68f3c7cd..b03d8f4c1cdf 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1883,20 +1883,14 @@ static int lo_open(struct block_device *bdev, fmode_t mode) int err; /* - * take loop_ctl_mutex to protect lo pointer from race with - * loop_control_ioctl(LOOP_CTL_REMOVE), however, to reduce contention - * release it prior to updating lo->lo_refcnt. + * both ->private_data and ->lo_refcnt are covered by disk's + * open_mutex, so race between open and remove can be avoided */ - err = mutex_lock_killable(&loop_ctl_mutex); - if (err) - return err; lo = bdev->bd_disk->private_data; - if (!lo) { - mutex_unlock(&loop_ctl_mutex); + if (!lo) return -ENXIO; - } + err = mutex_lock_killable(&lo->lo_mutex); - mutex_unlock(&loop_ctl_mutex); if (err) return err; atomic_inc(&lo->lo_refcnt); @@ -2272,21 +2266,26 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd, ret = loop_lookup(&lo, parm); if (ret < 0) break; - ret = mutex_lock_killable(&lo->lo_mutex); + /* cover removing vs. opening loop device */ + ret = mutex_lock_killable(&lo->lo_disk->part0->bd_mutex); if (ret) break; - if (lo->lo_state != Lo_unbound) { - ret = -EBUSY; - mutex_unlock(&lo->lo_mutex); + ret = mutex_lock_killable(&lo->lo_mutex); + if (ret) { + mutex_unlock(&lo->lo_disk->part0->bd_mutex); break; } - if (atomic_read(&lo->lo_refcnt) > 0) { + if (lo->lo_state != Lo_unbound || + atomic_read(&lo->lo_refcnt) > 0) { ret = -EBUSY; mutex_unlock(&lo->lo_mutex); + mutex_unlock(&lo->lo_disk->part0->bd_mutex); break; } - lo->lo_disk->private_data = NULL; mutex_unlock(&lo->lo_mutex); + lo->lo_disk->private_data = NULL; + mutex_unlock(&lo->lo_disk->part0->bd_mutex); + idr_remove(&loop_index_idr, lo->lo_number); loop_remove(lo); break; -- 2.29.2