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 CD8AFC433EF for ; Fri, 25 Feb 2022 08:49:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236360AbiBYIuI (ORCPT ); Fri, 25 Feb 2022 03:50:08 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45324 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234783AbiBYIuH (ORCPT ); Fri, 25 Feb 2022 03:50:07 -0500 Received: from mail-pl1-x629.google.com (mail-pl1-x629.google.com [IPv6:2607:f8b0:4864:20::629]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 750C21688F1 for ; Fri, 25 Feb 2022 00:49:35 -0800 (PST) Received: by mail-pl1-x629.google.com with SMTP id c9so4267722pll.0 for ; Fri, 25 Feb 2022 00:49:35 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=date:from:to:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=D5EFBPk5AwRLN6uJ/T4DmIbM4ozITAoaLk6FhzJSAXI=; b=kgouNLziSEEFchnU2pYOc3umDWUR9RA7FSU16dWqwanWB8EY20XR6hUatYrCm8NwHi CSR0ZZBJQuBFFATq7chUBMC3v2QW6b+8zUAAZ4BiTLjCqbf5VFWaU3eUgD1wLGhWDvGq Vy0UEaD86poqxD0IbIDMFGQoIydacn9vr7bQCjx1U5IhElWdYAPsLMqtIEQwFvEeyZZY 5SWWKUP/j8Bh+JlLA2nGVqvF7Voxp6wY8XZVIYx2UagFWzB61xLMnqQkMDSA8u9A5Y1P xZrMmJ1tJquJ37PbICHJ3Saff4aw3qoR076p29P/zRyQK+G5kWqY+K1ei4QX65B9Itg5 +TiA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=D5EFBPk5AwRLN6uJ/T4DmIbM4ozITAoaLk6FhzJSAXI=; b=Gk6yWa+LzYNwqCpSwbVwxKidyWvc4+EpsZC5Ey053hu7aIt6iw2oeLzYYIjaiq5h4j SCdn8dRpGQgccu6IpXOVcG/Ifq8OOw0HEgjWESGac7bj5DehelwXwOY4YDRII9MhVGkE Z5mWgNDMnm5Oz5YklSyeoMc/vOP3EA8L0+yd26DdXdq6AtFbSB/0aKV9zGKAKZXg/h8v tYgFbtuXh4HiW/pgjN2+Lfq6q6jXLKiTIjHNxQ//TwgME6sajaIBpqktmrDBiuOmafms 4MP9jI+ksU6+PuySGIWd9CRzcbG2+IeMewJ50k+jrarAuhLJjJDDKUmtccG1GufbcLci /UGQ== X-Gm-Message-State: AOAM533zU6f9lmCuZ+XFpJwsd0uRdkXd97W+/dntiHci4aFBpRu4xZsc 5HvTY42CIGpnbLPXXyFjkyY= X-Google-Smtp-Source: ABdhPJynZ9Ib65co4+Zj4kvGj+kxs+qT5CgAwWsSe7x78RwFq8TGFwx9P3l4JrJeSslq1R/K+euClQ== X-Received: by 2002:a17:90a:4590:b0:1bc:4afa:1778 with SMTP id v16-20020a17090a459000b001bc4afa1778mr2191270pjg.14.1645778974816; Fri, 25 Feb 2022 00:49:34 -0800 (PST) Received: from realwakka ([59.12.165.26]) by smtp.gmail.com with ESMTPSA id m11-20020a17090a3f8b00b001bc299e0aefsm8368806pjc.56.2022.02.25.00.49.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 25 Feb 2022 00:49:34 -0800 (PST) Date: Fri, 25 Feb 2022 08:49:26 +0000 From: Sidong Yang To: dsterba@suse.cz, 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: <20220225084926.GA14534@realwakka> References: <20220223095112.10880-1-realwakka@gmail.com> <20220224184803.GA12643@twin.jikos.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220224184803.GA12643@twin.jikos.cz> Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Thu, Feb 24, 2022 at 07:48:03PM +0100, David Sterba wrote: Hi, David. Thanks for reply. > On Wed, Feb 23, 2022 at 09:51:13AM +0000, Sidong Yang wrote: > > The patch e804861bd4e6 by Kawasaki > > Added to CC Thanks, I'll add CC for next patch. > > > 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. I agree. > > > 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. Yeah, I think it doesn't have side effects so far. But actually as a newbie, I didn't understood correctly that you said. I guess what you said is that there is no other cases that locks qgroup_ioctl_lock and thread removing qgroup goes deadlock again. It is right? > > > --- > > 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. I think this lock is needed for checking quota_root. Is it better that unlock right after checking it? It would make shorter ciritical section.