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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 95659C636C8 for ; Thu, 15 Jul 2021 22:50:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7A153613D2 for ; Thu, 15 Jul 2021 22:50:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232329AbhGOWxg (ORCPT ); Thu, 15 Jul 2021 18:53:36 -0400 Received: from relay8-d.mail.gandi.net ([217.70.183.201]:45791 "EHLO relay8-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232139AbhGOWxg (ORCPT ); Thu, 15 Jul 2021 18:53:36 -0400 Received: (Authenticated sender: miquel.raynal@bootlin.com) by relay8-d.mail.gandi.net (Postfix) with ESMTPSA id 79FB21BF208; Thu, 15 Jul 2021 22:50:40 +0000 (UTC) From: Miquel Raynal To: Desmond Cheong Zhi Xi , miquel.raynal@bootlin.com, richard@nod.at, vigneshr@ti.com Cc: linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org, skhan@linuxfoundation.org, gregkh@linuxfoundation.org, linux-kernel-mentees@lists.linuxfoundation.org, syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com, Christoph Hellwig Subject: Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans Date: Fri, 16 Jul 2021 00:50:40 +0200 Message-Id: <20210715225040.66117-1-miquel.raynal@bootlin.com> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20210617160904.570111-1-desmondcheongzx@gmail.com> References: MIME-Version: 1.0 X-linux-mtd-patch-notification: thanks X-linux-mtd-patch-commit: b'962bf783ef65d15b0f8ca9c33342cf3b20bf0d2e' Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2021-06-17 at 16:09:04 UTC, Desmond Cheong Zhi Xi wrote: > Syzbot reported a circular locking dependency: > https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb > > This happens because of the following lock dependencies: > > 1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls > loop_remove, which then calls del_gendisk; this also happens in > loop_exit which eventually calls loop_remove) > > 2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls > __blkdev_get, which then calls blktrans_open) > > 3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans > calls __register_blkdev) > > 4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls > loop_probe) > > Hence there's an overall dependency of: > > loop_ctl_mutex ----------> bdev->bd_mutex > ^ | > | | > | v > major_names_lock <--------- mtd_table_mutex > > We can break this circular dependency by holding mtd_table_mutex only > for the required critical section in register_mtd_blktrans. This > avoids the mtd_table_mutex -> major_names_lock dependency. > > Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com > Co-developed-by: Christoph Hellwig > Signed-off-by: Christoph Hellwig > Signed-off-by: Desmond Cheong Zhi Xi Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/fixes, thanks. Miquel