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=-10.3 required=3.0 tests=BAYES_00, 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 38982C47083 for ; Fri, 4 Jun 2021 06:57:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 140FB613F8 for ; Fri, 4 Jun 2021 06:57:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229896AbhFDG7W (ORCPT ); Fri, 4 Jun 2021 02:59:22 -0400 Received: from verein.lst.de ([213.95.11.211]:36450 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229831AbhFDG7V (ORCPT ); Fri, 4 Jun 2021 02:59:21 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 743C16736F; Fri, 4 Jun 2021 08:57:33 +0200 (CEST) Date: Fri, 4 Jun 2021 08:57:33 +0200 From: Christoph Hellwig To: Ming Lei Cc: Jens Axboe , Christoph Hellwig , linux-block@vger.kernel.org, Colin Ian King , Pavel Tatashin Subject: Re: [PATCH] block: loop: fix deadlock between open and remove Message-ID: <20210604065733.GA11135@lst.de> References: <20210604000424.189928-1-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210604000424.189928-1-ming.lei@redhat.com> User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org This looks good, but I think we can do simple by just adding add new Lo_deleting state. Completely untested as I'm at the tail end of a vacation with a broken laptop: diff --git a/drivers/block/loop.c b/drivers/block/loop.c index d58d68f3c7cd..76e12f3482a9 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1879,29 +1879,18 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode, static int lo_open(struct block_device *bdev, fmode_t mode) { - struct loop_device *lo; + struct loop_device *lo = bdev->bd_disk->private_data; 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. - */ - err = mutex_lock_killable(&loop_ctl_mutex); - if (err) - return err; - lo = bdev->bd_disk->private_data; - if (!lo) { - mutex_unlock(&loop_ctl_mutex); - return -ENXIO; - } err = mutex_lock_killable(&lo->lo_mutex); - mutex_unlock(&loop_ctl_mutex); if (err) return err; - atomic_inc(&lo->lo_refcnt); + if (lo->lo_state == Lo_deleting) + err = -ENXIO; + else + atomic_inc(&lo->lo_refcnt); mutex_unlock(&lo->lo_mutex); - return 0; + return err; } static void lo_release(struct gendisk *disk, fmode_t mode) @@ -2285,7 +2274,7 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd, mutex_unlock(&lo->lo_mutex); break; } - lo->lo_disk->private_data = NULL; + lo->lo_state = Lo_deleting; mutex_unlock(&lo->lo_mutex); idr_remove(&loop_index_idr, lo->lo_number); loop_remove(lo); diff --git a/drivers/block/loop.h b/drivers/block/loop.h index a3c04f310672..5beb959b94d3 100644 --- a/drivers/block/loop.h +++ b/drivers/block/loop.h @@ -22,6 +22,7 @@ enum { Lo_unbound, Lo_bound, Lo_rundown, + Lo_deleting, }; struct loop_func_table;