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=-12.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, 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 1F747C432BE for ; Thu, 2 Sep 2021 12:16:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 063C3603E9 for ; Thu, 2 Sep 2021 12:16:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344289AbhIBMRd (ORCPT ); Thu, 2 Sep 2021 08:17:33 -0400 Received: from smtp-out2.suse.de ([195.135.220.29]:50950 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234142AbhIBMRa (ORCPT ); Thu, 2 Sep 2021 08:17:30 -0400 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 694E21FF82; Thu, 2 Sep 2021 12:16:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1630584991; h=from:from:reply-to:reply-to:date:date:message-id:message-id:to:to: cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=7axcWPSwit16Vzh/j3OZqW05vqGlOv2Yiwr7+vt++A4=; b=l72HY3zxfJTIPeSvFHLDM0IHyJwi3s7kVY5Njoq/gzM+L5/EPh+gimMLAgxTP9zUvo+50Q qcU1AtSC9yse2ljenzYXRATCu8/tckw4EOtI7KArLnEh9gF2BVYjTuErwuHerXRZiyBlEZ WmaOVrqi7WzHs0YYfgRQpLj9Boe2Fx4= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1630584991; h=from:from:reply-to:reply-to:date:date:message-id:message-id:to:to: cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=7axcWPSwit16Vzh/j3OZqW05vqGlOv2Yiwr7+vt++A4=; b=0yiE+UR2hjI8aqupbWUBfUYpvgQFWJXNocbjxvB9dL9UvpP5aRF+Kq6hnAfIMWEuoV8Lec W803wzzK6VunRbDg== Received: from ds.suse.cz (ds.suse.cz [10.100.12.205]) by relay2.suse.de (Postfix) with ESMTP id 579DCA3BB8; Thu, 2 Sep 2021 12:16:31 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id 4C635DA72B; Thu, 2 Sep 2021 14:16:30 +0200 (CEST) Date: Thu, 2 Sep 2021 14:16:30 +0200 From: David Sterba To: Josef Bacik Cc: linux-btrfs@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH v2 5/7] btrfs: delay blkdev_put until after the device remove Message-ID: <20210902121630.GQ3379@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Josef Bacik , linux-btrfs@vger.kernel.org, kernel-team@fb.com References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Tue, Jul 27, 2021 at 05:01:17PM -0400, Josef Bacik wrote: > When removing the device we call blkdev_put() on the device once we've > removed it, and because we have an EXCL open we need to take the > ->open_mutex on the block device to clean it up. Unfortunately during > device remove we are holding the sb writers lock, which results in the > following lockdep splat > > ====================================================== > WARNING: possible circular locking dependency detected > 5.14.0-rc2+ #407 Not tainted > ------------------------------------------------------ > losetup/11595 is trying to acquire lock: > ffff973ac35dd138 ((wq_completion)loop0){+.+.}-{0:0}, at: flush_workqueue+0x67/0x5e0 > > but task is already holding lock: > ffff973ac9812c68 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0x41/0x660 [loop] > > which lock already depends on the new lock. > > the existing dependency chain (in reverse order) is: > > -> #4 (&lo->lo_mutex){+.+.}-{3:3}: > __mutex_lock+0x7d/0x750 > lo_open+0x28/0x60 [loop] > blkdev_get_whole+0x25/0xf0 > blkdev_get_by_dev.part.0+0x168/0x3c0 > blkdev_open+0xd2/0xe0 > do_dentry_open+0x161/0x390 > path_openat+0x3cc/0xa20 > do_filp_open+0x96/0x120 > do_sys_openat2+0x7b/0x130 > __x64_sys_openat+0x46/0x70 > do_syscall_64+0x38/0x90 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > -> #3 (&disk->open_mutex){+.+.}-{3:3}: > __mutex_lock+0x7d/0x750 > blkdev_put+0x3a/0x220 > btrfs_rm_device.cold+0x62/0xe5 > btrfs_ioctl+0x2a31/0x2e70 > __x64_sys_ioctl+0x80/0xb0 > do_syscall_64+0x38/0x90 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > -> #2 (sb_writers#12){.+.+}-{0:0}: > lo_write_bvec+0xc2/0x240 [loop] > loop_process_work+0x238/0xd00 [loop] > process_one_work+0x26b/0x560 > worker_thread+0x55/0x3c0 > kthread+0x140/0x160 > ret_from_fork+0x1f/0x30 > > -> #1 ((work_completion)(&lo->rootcg_work)){+.+.}-{0:0}: > process_one_work+0x245/0x560 > worker_thread+0x55/0x3c0 > kthread+0x140/0x160 > ret_from_fork+0x1f/0x30 > > -> #0 ((wq_completion)loop0){+.+.}-{0:0}: > __lock_acquire+0x10ea/0x1d90 > lock_acquire+0xb5/0x2b0 > flush_workqueue+0x91/0x5e0 > drain_workqueue+0xa0/0x110 > destroy_workqueue+0x36/0x250 > __loop_clr_fd+0x9a/0x660 [loop] > block_ioctl+0x3f/0x50 > __x64_sys_ioctl+0x80/0xb0 > do_syscall_64+0x38/0x90 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > other info that might help us debug this: > > Chain exists of: > (wq_completion)loop0 --> &disk->open_mutex --> &lo->lo_mutex > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(&lo->lo_mutex); > lock(&disk->open_mutex); > lock(&lo->lo_mutex); > lock((wq_completion)loop0); > > *** DEADLOCK *** > > 1 lock held by losetup/11595: > #0: ffff973ac9812c68 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0x41/0x660 [loop] > > stack backtrace: > CPU: 0 PID: 11595 Comm: losetup Not tainted 5.14.0-rc2+ #407 > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014 > Call Trace: > dump_stack_lvl+0x57/0x72 > check_noncircular+0xcf/0xf0 > ? stack_trace_save+0x3b/0x50 > __lock_acquire+0x10ea/0x1d90 > lock_acquire+0xb5/0x2b0 > ? flush_workqueue+0x67/0x5e0 > ? lockdep_init_map_type+0x47/0x220 > flush_workqueue+0x91/0x5e0 > ? flush_workqueue+0x67/0x5e0 > ? verify_cpu+0xf0/0x100 > drain_workqueue+0xa0/0x110 > destroy_workqueue+0x36/0x250 > __loop_clr_fd+0x9a/0x660 [loop] > ? blkdev_ioctl+0x8d/0x2a0 > block_ioctl+0x3f/0x50 > __x64_sys_ioctl+0x80/0xb0 > do_syscall_64+0x38/0x90 > entry_SYSCALL_64_after_hwframe+0x44/0xae > RIP: 0033:0x7fc21255d4cb > > So instead save the bdev and do the put once we've dropped the sb > writers lock in order to avoid the lockdep recursion. > > Signed-off-by: Josef Bacik Added to misc-next, thanks.