From patchwork Thu Sep 27 11:36:51 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jan Kara X-Patchwork-Id: 10617829 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 2D7DE1759 for ; Thu, 27 Sep 2018 11:37:15 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 1E33D2B1FB for ; Thu, 27 Sep 2018 11:37:15 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 12DF42B200; Thu, 27 Sep 2018 11:37:15 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A25022B208 for ; Thu, 27 Sep 2018 11:37:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727182AbeI0RzF (ORCPT ); Thu, 27 Sep 2018 13:55:05 -0400 Received: from mx2.suse.de ([195.135.220.15]:37112 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727145AbeI0RzF (ORCPT ); Thu, 27 Sep 2018 13:55:05 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 03A98B12A; Thu, 27 Sep 2018 11:37:10 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id B1D871E3BE0; Thu, 27 Sep 2018 13:37:09 +0200 (CEST) From: Jan Kara To: Jens Axboe Cc: , Tetsuo Handa , Jan Kara Subject: [PATCH 13/14] loop: Move loop_reread_partitions() out of loop_ctl_mutex Date: Thu, 27 Sep 2018 13:36:51 +0200 Message-Id: <20180927113652.5422-14-jack@suse.cz> X-Mailer: git-send-email 2.16.4 In-Reply-To: <20180927113652.5422-1-jack@suse.cz> References: <20180927113652.5422-1-jack@suse.cz> Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Calling loop_reread_partitions() under loop_ctl_mutex causes lockdep to complain about circular lock dependency between bdev->bd_mutex and lo->lo_ctl_mutex. The problem is that on loop device open or close lo_open() and lo_release() get called with bdev->bd_mutex held and they need to acquire loop_ctl_mutex. OTOH when loop_reread_partitions() is called with loop_ctl_mutex held, it will call blkdev_reread_part() which acquires bdev->bd_mutex. See syzbot report for details [1]. Move all calls of loop_rescan_partitions() out of loop_ctl_mutex to avoid lockdep warning and fix deadlock possibility. [1] https://syzkaller.appspot.com/bug?id=bf154052f0eea4bc7712499e4569505907d1588 Reported-by: syzbot Signed-off-by: Jan Kara --- drivers/block/loop.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index cce1a32ae6d0..d2be85c48f03 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -680,6 +680,7 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, { struct file *file, *old_file; int error; + bool partscan; error = mutex_lock_killable_nested(&loop_ctl_mutex, 1); if (error) @@ -721,9 +722,10 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, blk_mq_unfreeze_queue(lo->lo_queue); fput(old_file); - if (lo->lo_flags & LO_FLAGS_PARTSCAN) - loop_reread_partitions(lo, bdev); + partscan = lo->lo_flags & LO_FLAGS_PARTSCAN; mutex_unlock(&loop_ctl_mutex); + if (partscan) + loop_reread_partitions(lo, bdev); return 0; out_putf: @@ -904,6 +906,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, int lo_flags = 0; int error; loff_t size; + bool partscan; /* This is safe, since we have a reference from open(). */ __module_get(THIS_MODULE); @@ -970,14 +973,15 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, lo->lo_state = Lo_bound; if (part_shift) lo->lo_flags |= LO_FLAGS_PARTSCAN; - if (lo->lo_flags & LO_FLAGS_PARTSCAN) - loop_reread_partitions(lo, bdev); + partscan = lo->lo_flags & LO_FLAGS_PARTSCAN; /* Grab the block_device to prevent its destruction after we * put /dev/loopXX inode. Later in __loop_clr_fd() we bdput(bdev). */ bdgrab(bdev); mutex_unlock(&loop_ctl_mutex); + if (partscan) + loop_reread_partitions(lo, bdev); return 0; out_unlock: @@ -1158,6 +1162,8 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info) int err; struct loop_func_table *xfer; kuid_t uid = current_uid(); + struct block_device *bdev; + bool partscan = false; err = mutex_lock_killable_nested(&loop_ctl_mutex, 1); if (err) @@ -1246,10 +1252,13 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info) !(lo->lo_flags & LO_FLAGS_PARTSCAN)) { lo->lo_flags |= LO_FLAGS_PARTSCAN; lo->lo_disk->flags &= ~GENHD_FL_NO_PART_SCAN; - loop_reread_partitions(lo, lo->lo_device); + bdev = lo->lo_device; + partscan = true; } out_unlock: mutex_unlock(&loop_ctl_mutex); + if (partscan) + loop_reread_partitions(lo, bdev); return err; }