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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E4F89C433EF for ; Thu, 24 Feb 2022 18:51:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232432AbiBXSw0 (ORCPT ); Thu, 24 Feb 2022 13:52:26 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57786 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229850AbiBXSwY (ORCPT ); Thu, 24 Feb 2022 13:52:24 -0500 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E587C18DAA0 for ; Thu, 24 Feb 2022 10:51:53 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id A019B210DF; Thu, 24 Feb 2022 18:51:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1645728712; 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=Dz6WreNXK0lwyBKwoVl2EvvY45CcF2UbMLNaxNz7EUo=; b=Jl0muDH588Hz1AuyULbCW7PGp/CmEfiyAcpNC4w6XXXMUQ3cptWye/3OJU4gF0xqoSlVYK G4vZMNvn3fd2ARmvU+EBaCRt0O1NCayX46PNKveAH6QRIYq08WYVHNshMyYS65OJULZW9H rasvjTWM1YHoPxY5SX+faFdGq9LmDGs= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1645728712; 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=Dz6WreNXK0lwyBKwoVl2EvvY45CcF2UbMLNaxNz7EUo=; b=XXhRBcsV4mvYQ20G+FX5kR4R6zm8VRel0ic0qtPfdpreOe7MXmRzaJOWCzzEldJNMve04/ fZSkLotMth84ZdDw== Received: from ds.suse.cz (ds.suse.cz [10.100.12.205]) by relay2.suse.de (Postfix) with ESMTP id 6C7E0A3B87; Thu, 24 Feb 2022 18:51:52 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id 863B7DA818; Thu, 24 Feb 2022 19:48:03 +0100 (CET) Date: Thu, 24 Feb 2022 19:48:03 +0100 From: David Sterba To: Sidong Yang Cc: linux-btrfs@vger.kernel.org, shinichiro.kawasaki@wdc.com Subject: Re: [RFC PATCH] btrfs: qgroup: fix deadlock between rescan worker and remove qgroup Message-ID: <20220224184803.GA12643@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Sidong Yang , linux-btrfs@vger.kernel.org, shinichiro.kawasaki@wdc.com References: <20220223095112.10880-1-realwakka@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220223095112.10880-1-realwakka@gmail.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Wed, Feb 23, 2022 at 09:51:13AM +0000, Sidong Yang wrote: > The patch e804861bd4e6 by Kawasaki Added to CC > resolves deadlock between quota > disable and qgroup rescan worker. but also there is a deadlock case like > it. It's about enabling or disabling quota and creating or removing > qgroup. It can be reproduced in simple script below. > > for i in {1..100} > do > btrfs quota enable /mnt & > btrfs qgroup create 1/0 /mnt & > btrfs qgroup destroy 1/0 /mnt & > btrfs quota disable /mnt & > done > > This script simply enables quota and creates/destroies qgroup and disables > qgroup 100 times. Enabling quota starts rescan worker and it commits > transaction and wait in wait_for_commit(). transaction_kthread would > wakup for the commit and try to attach trasaction but there would be > another current transaction. The transaction was from another command > that destroy qgroup. but destroying qgroup could be blocked by > qgroup_ioctl_lock which locked by the thread disabling quota. That looks like the cause. > An example report of the deadlock: > > [ 363.661448] INFO: task kworker/u16:4:295 blocked for more than 120 seconds. > [ 363.661582] Not tainted 5.17.0-rc4+ #16 > [ 363.661659] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > [ 363.661744] task:kworker/u16:4 state:D stack: 0 pid: 295 ppid: 2 flags:0x00004000 > [ 363.661762] Workqueue: btrfs-qgroup-rescan btrfs_work_helper [btrfs] > [ 363.661936] Call Trace: > [ 363.661949] > [ 363.661958] __schedule+0x2e5/0xbb0 > [ 363.662002] ? btrfs_free_path+0x27/0x30 [btrfs] > [ 363.662094] ? mutex_lock+0x13/0x40 > [ 363.662106] schedule+0x58/0xd0 > [ 363.662116] btrfs_commit_transaction+0x2dc/0xb40 [btrfs] > [ 363.662250] ? wait_woken+0x60/0x60 > [ 363.662271] btrfs_qgroup_rescan_worker+0x3cb/0x600 [btrfs] > [ 363.662419] btrfs_work_helper+0xc8/0x330 [btrfs] > [ 363.662551] process_one_work+0x21a/0x3f0 > [ 363.662588] worker_thread+0x4a/0x3b0 > [ 363.662600] ? process_one_work+0x3f0/0x3f0 > [ 363.662609] kthread+0xfd/0x130 > [ 363.662618] ? kthread_complete_and_exit+0x20/0x20 > [ 363.662628] ret_from_fork+0x1f/0x30 > [ 363.662659] > [ 363.662691] INFO: task btrfs-transacti:1158 blocked for more than 120 seconds. > [ 363.662765] Not tainted 5.17.0-rc4+ #16 > [ 363.662809] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > [ 363.662880] task:btrfs-transacti state:D stack: 0 pid: 1158 ppid: 2 flags:0x00004000 > [ 363.662889] Call Trace: > [ 363.662892] > [ 363.662896] __schedule+0x2e5/0xbb0 > [ 363.662906] ? _raw_spin_lock_irqsave+0x2a/0x60 > [ 363.662925] schedule+0x58/0xd0 > [ 363.662942] wait_current_trans+0xd2/0x130 [btrfs] > [ 363.663046] ? wait_woken+0x60/0x60 > [ 363.663055] start_transaction+0x33c/0x600 [btrfs] > [ 363.663159] btrfs_attach_transaction+0x1d/0x20 [btrfs] > [ 363.663268] transaction_kthread+0xb5/0x1b0 [btrfs] > [ 363.663368] ? btrfs_cleanup_transaction+0x580/0x580 [btrfs] > [ 363.663465] kthread+0xfd/0x130 > [ 363.663475] ? kthread_complete_and_exit+0x20/0x20 > [ 363.663484] ret_from_fork+0x1f/0x30 > [ 363.663498] > [ 363.663503] INFO: task btrfs:81196 blocked for more than 120 seconds. > [ 363.663568] Not tainted 5.17.0-rc4+ #16 > [ 363.663612] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > [ 363.663693] task:btrfs state:D stack: 0 pid:81196 ppid: 1 flags:0x00000000 > [ 363.663702] Call Trace: > [ 363.663705] > [ 363.663709] __schedule+0x2e5/0xbb0 > [ 363.663721] schedule+0x58/0xd0 > [ 363.663729] rwsem_down_write_slowpath+0x310/0x5b0 > [ 363.663748] ? __check_object_size+0x130/0x150 > [ 363.663770] down_write+0x41/0x50 > [ 363.663780] btrfs_ioctl+0x20e6/0x2f40 [btrfs] > [ 363.663918] ? debug_smp_processor_id+0x17/0x20 > [ 363.663932] ? fpregs_assert_state_consistent+0x23/0x50 > [ 363.663963] __x64_sys_ioctl+0x8e/0xc0 > [ 363.663981] ? __x64_sys_ioctl+0x8e/0xc0 > [ 363.663990] do_syscall_64+0x38/0xc0 > [ 363.663998] entry_SYSCALL_64_after_hwframe+0x44/0xae > [ 363.664006] RIP: 0033:0x7f1082add50b > [ 363.664014] RSP: 002b:00007fffbfd1ba98 EFLAGS: 00000206 ORIG_RAX: 0000000000000010 > [ 363.664022] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f1082add50b > [ 363.664028] RDX: 00007fffbfd1bab0 RSI: 00000000c0109428 RDI: 0000000000000003 > [ 363.664032] RBP: 0000000000000003 R08: 000055e4263142a0 R09: 000000000000007c > [ 363.664036] R10: 00007f1082bb1be0 R11: 0000000000000206 R12: 00007fffbfd1c723 > [ 363.664040] R13: 0000000000000001 R14: 000055e42615408d R15: 00007fffbfd1bc68 > [ 363.664049] > [ 363.664053] INFO: task btrfs:81197 blocked for more than 120 seconds. > [ 363.664117] Not tainted 5.17.0-rc4+ #16 > [ 363.664160] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > [ 363.664231] task:btrfs state:D stack: 0 pid:81197 ppid: 1 flags:0x00000000 > [ 363.664239] Call Trace: > [ 363.664241] > [ 363.664245] __schedule+0x2e5/0xbb0 > [ 363.664257] schedule+0x58/0xd0 > [ 363.664265] rwsem_down_write_slowpath+0x310/0x5b0 > [ 363.664274] ? __check_object_size+0x130/0x150 > [ 363.664282] down_write+0x41/0x50 > [ 363.664292] btrfs_ioctl+0x20e6/0x2f40 [btrfs] > [ 363.664430] ? debug_smp_processor_id+0x17/0x20 > [ 363.664442] ? fpregs_assert_state_consistent+0x23/0x50 > [ 363.664453] __x64_sys_ioctl+0x8e/0xc0 > [ 363.664462] ? __x64_sys_ioctl+0x8e/0xc0 > [ 363.664470] do_syscall_64+0x38/0xc0 > [ 363.664478] entry_SYSCALL_64_after_hwframe+0x44/0xae > [ 363.664484] RIP: 0033:0x7ff1752ac50b > [ 363.664489] RSP: 002b:00007ffc0cb56eb8 EFLAGS: 00000206 ORIG_RAX: 0000000000000010 > [ 363.664495] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007ff1752ac50b > [ 363.664500] RDX: 00007ffc0cb56ed0 RSI: 00000000c0109428 RDI: 0000000000000003 > [ 363.664503] RBP: 0000000000000003 R08: 000055d0dcf182a0 R09: 000000000000007c > [ 363.664507] R10: 00007ff175380be0 R11: 0000000000000206 R12: 00007ffc0cb58723 > [ 363.664520] R13: 0000000000000001 R14: 000055d0db04708d R15: 00007ffc0cb57088 > [ 363.664528] > [ 363.664532] INFO: task btrfs:81204 blocked for more than 120 seconds. > [ 363.664596] Not tainted 5.17.0-rc4+ #16 > [ 363.664639] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > [ 363.664710] task:btrfs state:D stack: 0 pid:81204 ppid: 1 flags:0x00004000 > [ 363.664717] Call Trace: > [ 363.664720] > [ 363.664723] __schedule+0x2e5/0xbb0 > [ 363.664735] schedule+0x58/0xd0 > [ 363.664743] schedule_timeout+0x1f3/0x290 > [ 363.664754] ? __mutex_lock.isra.0+0x8f/0x4c0 > [ 363.664765] wait_for_completion+0x8b/0xf0 > [ 363.664776] btrfs_qgroup_wait_for_completion+0x62/0x70 [btrfs] > [ 363.664995] btrfs_quota_disable+0x51/0x320 [btrfs] > [ 363.665136] btrfs_ioctl+0x2106/0x2f40 [btrfs] > [ 363.665385] ? debug_smp_processor_id+0x17/0x20 > [ 363.665402] ? fpregs_assert_state_consistent+0x23/0x50 > [ 363.665417] __x64_sys_ioctl+0x8e/0xc0 > [ 363.665428] ? __x64_sys_ioctl+0x8e/0xc0 > [ 363.665439] do_syscall_64+0x38/0xc0 > [ 363.665450] entry_SYSCALL_64_after_hwframe+0x44/0xae > [ 363.665459] RIP: 0033:0x7f9d7462050b > [ 363.665466] RSP: 002b:00007ffc1de68558 EFLAGS: 00000206 ORIG_RAX: 0000000000000010 > [ 363.665475] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f9d7462050b > [ 363.665480] RDX: 00007ffc1de68570 RSI: 00000000c0109428 RDI: 0000000000000003 > [ 363.665486] RBP: 0000000000000003 R08: 00005629e953b2a0 R09: 000000000000007c > [ 363.665492] R10: 00007f9d746f4be0 R11: 0000000000000206 R12: 00007ffc1de69723 > [ 363.665498] R13: 0000000000000001 R14: 00005629e8e5708d R15: 00007ffc1de68728 > [ 363.665510] > > To resolve this issue, The thread disabling quota should unlock > qgroup_ioctl_lock before waiting rescan completion. This patch moves > btrfs_qgroup_wait_for_completion() after qgroup_ioctl_lock(). > > Signed-off-by: Sidong Yang > --- > Hi, I found some deadlock bug with testing a simple script. > With this patch, it seems that it resolves it. but I don't know much about how > transaction works. and I'm afraid that it has other side effects. I had a quick look and did not see anything obvious, the qgroup waiting is done in onther contexts without any apparent conditions or other restrictions. > --- > fs/btrfs/qgroup.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c > index 2c0dd6b8a80c..85e5b3572dda 100644 > --- a/fs/btrfs/qgroup.c > +++ b/fs/btrfs/qgroup.c > @@ -1219,8 +1219,8 @@ int btrfs_quota_disable(struct btrfs_fs_info *fs_info) > * deadlock with transaction by the qgroup rescan worker. > */ > clear_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags); > - btrfs_qgroup_wait_for_completion(fs_info, false); > mutex_unlock(&fs_info->qgroup_ioctl_lock); > + btrfs_qgroup_wait_for_completion(fs_info, false); Yeah waiting with a mutex held can lead to problems unless the locks are compatible in that way.