From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f175.google.com (mail-pl1-f175.google.com [209.85.214.175]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E7B161509AB for ; Mon, 20 Apr 2026 01:41:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.175 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776649285; cv=none; b=YdAuSzoqappPtoCjRXOR6wE9fCWnc/O2aGpnsOYckUis0kdzSBZxN58uV3wWT/VZr0PJ7BGeYzTUZW/W+PBecWWOxXsQbJe8zPcUAKrtbqu2wW+GbojP6GD+kG/CcDJ+n3rv1PVWz56G6KFZWKdDT2rZ9j+zS5VHdVJkQjFsyGo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776649285; c=relaxed/simple; bh=TnaZC2FzerV/jS4YKe+r2pAcUgSAi1aYfCVm4uQjIpo=; h=Message-ID:Date:MIME-Version:From:Subject:To:Cc:References: In-Reply-To:Content-Type; b=ri+MyF6inOj1aO85fHu9AVsHWAfezealUW6dI2hJpVO5GEDQsZ3w1c4g90pgyAumMcC9Me09ndDS5bTQMrFYotV/QOrAYKCzgsYXr3twQgz2AdTC/DEKs4zygIuOUuzttK/l+qVuUlVXRAxX9k1UQLO6bVPvYLSd9itoxHidhvA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=Z/h+QLET; arc=none smtp.client-ip=209.85.214.175 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Z/h+QLET" Received: by mail-pl1-f175.google.com with SMTP id d9443c01a7336-2b299b3c739so10794835ad.3 for ; Sun, 19 Apr 2026 18:41:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1776649283; x=1777254083; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:content-language:references :cc:to:subject:from:user-agent:mime-version:date:message-id:from:to :cc:subject:date:message-id:reply-to; bh=wdlhCJyNP6uETW2T3gVyDMyYByBkuzxax7waVBvXPPU=; b=Z/h+QLETgvNCj398TKgiIrL0TPGQ9B1+/5ik5mJF5Pa0pJVzdkRQDhVavdDzWe1TSg KNw5KzXS0BHi5ZfXFux1KfvXf3WUhWVlvXCD/aMX5EUR2AnsZ8POOaQGbD9sZS3lefaN EjHMLNEYFQ3Zfjv1WbDF4mmFmeg+AgCj4nJfbgZRV0GSQSxHcwZMU5SU2KejC4O2Vfhu vjsoJki5dIOp+SxPwBdVwtBFyLq8IIkDKt//IM54OQGxz9Ii7F13cbaawhUQeRx1GePC +LrNgCA8vMVc9WZ+erjbbACYgbKgh48dqhyXechKx28TAMiN1vaoUC9ceT7SwNQ/bGVo +7IA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1776649283; x=1777254083; h=content-transfer-encoding:in-reply-to:content-language:references :cc:to:subject:from:user-agent:mime-version:date:message-id:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=wdlhCJyNP6uETW2T3gVyDMyYByBkuzxax7waVBvXPPU=; b=jMuX7EgF8nw5l4oFNpSg4Isn9NhZITZF/x5LFbbTIIjNjW2zKPYnMF03pL9Uhnyn3h 8NsRwjG242Kpkj+BORfz/Kb7fIU7uEDUa8wVfwbaBs/ZYGKd07+SIHCFKRczTAylJNVy m90TDMC3sXSPvCFtqAGWa9M0IOL1yHGNQnvIumIwwiQhOLzje2YSH8Mxq+AEocGNyxfq BHFSBzzK1qI9Vj2Ijwl7eNgyYaJiXSjczKrL+vxm4ZRfFdBI5AbvIdPxqGsWrUx+tcD0 +u2WHh2cjTZFKk3k+EbPOfK0xNLmjilUiCfzFtwu4TGzUi1UlVIBMcGCJzNLVbnihJuu N60w== X-Forwarded-Encrypted: i=1; AFNElJ9b5ZDqNtORBiIuiUqmRVRyqCVmWfZekoTuxZ2/Ql9Dq+B5Ecnx/RZk9ryuDIbcktgTVgwJb3DojJBYRgs=@vger.kernel.org X-Gm-Message-State: AOJu0YzAAqL1ztph1/W+LeKTZZhZtU/4W0YyMja/ZI1UsZg+KfGYrn5k zFuIv51qwWjPWMrHnHFv5BXnvtjYOgfiFH8KNshmaRGrYo42qIg2OiK4 X-Gm-Gg: AeBDievWHDPuQu9SvQzjSZ6YJmWzMxPZOJmo8D6Z/asr42VlbEY+qnALkh9n4IZ7ofB 7Ye3NwAuSxkaEw3qnNBJTgg8yuZk5IpHv3Cmhi/wDPaaCa/h4aAiKZ2TsixH4UeFAS1+8Ku0gbi nqKuREG1AYs7yS1a6juxb3Uz9//Oz0jYrlnkb3gYadMe5PosznidReXRLmLl5bJ5n4VW0nIt6aw tmGlC+/xr6GqCTkUyydrZPE5d9+kmORCbaaA5w75hzMyZZYW7dOHCQczs6x/o1Eduiz1ai3C9vQ LnuajKE3B19fC8NCuUkVvFmHhRXVlIzUmmQYExFxcxIbjsxe9s+rWxpPrn0mite6eR+Lj+ExHVu LxK/8SMglAd+us4FFXdcymh04sZYYlEGU1vc2Gqn1d16/qNIGmndkjuyZ1Wsa4SkmYAYgUa1dgp UTXrkUZaaothfHDjToiuk2OQStU9r/c6C9uV5N1+1o/KgerZyX X-Received: by 2002:a17:902:bd85:b0:2b4:5e0f:c239 with SMTP id d9443c01a7336-2b5f9eaa80bmr74815805ad.10.1776649283232; Sun, 19 Apr 2026 18:41:23 -0700 (PDT) Received: from [10.121.80.58] ([210.184.73.204]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b5fab29398sm86217945ad.66.2026.04.19.18.41.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 19 Apr 2026 18:41:22 -0700 (PDT) Message-ID: <6903fe2d-ce67-4e9b-a5bc-d71da50450d5@gmail.com> Date: Mon, 20 Apr 2026 09:41:18 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Ruipeng Qi Subject: Re: [PATCH] f2fs: fix potential deadlock in f2fs_balance_fs() To: jaegeuk@kernel.org Cc: chao@kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org References: <20260325133749.1053541-1-ruipengqi3@gmail.com> Content-Language: en-US In-Reply-To: <20260325133749.1053541-1-ruipengqi3@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2026/3/25 21:37, ruipengqi wrote: > From: Ruipeng Qi > > When the f2fs filesystem space is nearly exhausted, we encounter deadlock > issues as below: > > INFO: task A:1890 blocked for more than 120 seconds. > Tainted: G O 6.12.41-g3fe07ddf05ab #1 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:A state:D stack:0 pid:1890 tgid:1626 ppid:1153 flags:0x00000204 > Call trace: > __switch_to+0xf4/0x158 > __schedule+0x27c/0x908 > schedule+0x3c/0x118 > io_schedule+0x44/0x68 > folio_wait_bit_common+0x174/0x370 > folio_wait_bit+0x20/0x38 > folio_wait_writeback+0x54/0xc8 > truncate_inode_partial_folio+0x70/0x1e0 > truncate_inode_pages_range+0x1b0/0x450 > truncate_pagecache+0x54/0x88 > f2fs_file_write_iter+0x3e8/0xb80 > do_iter_readv_writev+0xf0/0x1e0 > vfs_writev+0x138/0x2c8 > do_writev+0x88/0x130 > __arm64_sys_writev+0x28/0x40 > invoke_syscall+0x50/0x120 > el0_svc_common.constprop.0+0xc8/0xf0 > do_el0_svc+0x24/0x38 > el0_svc+0x30/0xf8 > el0t_64_sync_handler+0x120/0x130 > el0t_64_sync+0x190/0x198 > > INFO: task kworker/u8:11:2680853 blocked for more than 120 seconds. > Tainted: G O 6.12.41-g3fe07ddf05ab #1 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:kworker/u8:11 state:D stack:0 pid:2680853 tgid:2680853 ppid:2 flags:0x00000208 > Workqueue: writeback wb_workfn (flush-254:0) > Call trace: > __switch_to+0xf4/0x158 > __schedule+0x27c/0x908 > schedule+0x3c/0x118 > io_schedule+0x44/0x68 > folio_wait_bit_common+0x174/0x370 > __filemap_get_folio+0x214/0x348 > pagecache_get_page+0x20/0x70 > f2fs_get_read_data_page+0x150/0x3e8 > f2fs_get_lock_data_page+0x2c/0x160 > move_data_page+0x50/0x478 > do_garbage_collect+0xd38/0x1528 > f2fs_gc+0x240/0x7e0 > f2fs_balance_fs+0x1a0/0x208 > f2fs_write_single_data_page+0x6e4/0x730 //0xfffffe0d6ca08300 > f2fs_write_cache_pages+0x378/0x9b0 > f2fs_write_data_pages+0x2e4/0x388 > do_writepages+0x8c/0x2c8 > __writeback_single_inode+0x4c/0x498 > writeback_sb_inodes+0x234/0x4a8 > __writeback_inodes_wb+0x58/0x118 > wb_writeback+0x2f8/0x3c0 > wb_workfn+0x2c4/0x508 > process_one_work+0x180/0x408 > worker_thread+0x258/0x368 > kthread+0x118/0x128 > ret_from_fork+0x10/0x200 > > INFO: task kworker/u8:8:2641297 blocked for more than 120 seconds. > Tainted: G O 6.12.41-g3fe07ddf05ab #1 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:kworker/u8:8 state:D stack:0 pid:2641297 tgid:2641297 ppid:2 flags:0x00000208 > Workqueue: writeback wb_workfn (flush-254:0) > Call trace: > __switch_to+0xf4/0x158 > __schedule+0x27c/0x908 > rt_mutex_schedule+0x30/0x60 > __rt_mutex_slowlock_locked.constprop.0+0x460/0x8a8 > rwbase_write_lock+0x24c/0x378 > down_write+0x1c/0x30 > f2fs_balance_fs+0x184/0x208 > f2fs_write_inode+0xf4/0x328 > __writeback_single_inode+0x370/0x498 > writeback_sb_inodes+0x234/0x4a8 > __writeback_inodes_wb+0x58/0x118 > wb_writeback+0x2f8/0x3c0 > wb_workfn+0x2c4/0x508 > process_one_work+0x180/0x408 > worker_thread+0x258/0x368 > kthread+0x118/0x128 > ret_from_fork+0x10/0x20 > > INFO: task B:1902 blocked for more than 120 seconds. > Tainted: G O 6.12.41-g3fe07ddf05ab #1 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:B state:D stack:0 pid:1902 tgid:1626 ppid:1153 flags:0x0000020c > Call trace: > __switch_to+0xf4/0x158 > __schedule+0x27c/0x908 > rt_mutex_schedule+0x30/0x60 > __rt_mutex_slowlock_locked.constprop.0+0x460/0x8a8 > rwbase_write_lock+0x24c/0x378 > down_write+0x1c/0x30 > f2fs_balance_fs+0x184/0x208 > f2fs_map_blocks+0x94c/0x1110 > f2fs_file_write_iter+0x228/0xb80 > do_iter_readv_writev+0xf0/0x1e0 > vfs_writev+0x138/0x2c8 > do_writev+0x88/0x130 > __arm64_sys_writev+0x28/0x40 > invoke_syscall+0x50/0x120 > el0_svc_common.constprop.0+0xc8/0xf0 > do_el0_svc+0x24/0x38 > el0_svc+0x30/0xf8 > el0t_64_sync_handler+0x120/0x130 > el0t_64_sync+0x190/0x198 > > INFO: task sync:2769849 blocked for more than 120 seconds. > Tainted: G O 6.12.41-g3fe07ddf05ab #1 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:sync state:D stack:0 pid:2769849 tgid:2769849 ppid:736 flags:0x0000020c > Call trace: > __switch_to+0xf4/0x158 > __schedule+0x27c/0x908 > schedule+0x3c/0x118 > wb_wait_for_completion+0xb0/0xe8 > sync_inodes_sb+0xc8/0x2b0 > sync_inodes_one_sb+0x24/0x38 > iterate_supers+0xa8/0x138 > ksys_sync+0x54/0xc8 > __arm64_sys_sync+0x18/0x30 > invoke_syscall+0x50/0x120 > el0_svc_common.constprop.0+0xc8/0xf0 > do_el0_svc+0x24/0x38 > el0_svc+0x30/0xf8 > el0t_64_sync_handler+0x120/0x130 > el0t_64_sync+0x190/0x198 > > The root cause is a potential deadlock between the following tasks: > > kworker/u8:11 Thread A > - f2fs_write_single_data_page > - f2fs_do_write_data_page > - folio_start_writeback(X) > - f2fs_outplace_write_data > - bio_add_folio(X) > - folio_unlock(X) > - truncate_inode_pages_range > - __filemap_get_folio(X, FGP_LOCK) > - truncate_inode_partial_folio(X) > - folio_wait_writeback(X) > - f2fs_balance_fs > - f2fs_gc > - do_garbage_collect > - move_data_page > - f2fs_get_lock_data_page > - __filemap_get_folio(X, FGP_LOCK) > > Both threads try to access folio X. Thread A holds the lock but waits > for writeback, while kworker waits for the lock. This causes a deadlock. > > Other threads also enter D state, waiting for locks such as gc_lock and > writepages. > > To avoid this potential deadlock, always call f2fs_submit_merged_write > before triggering f2fs_gc in f2fs_balance_fs. > > Signed-off-by: Ruipeng Qi > --- > fs/f2fs/segment.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c > index 6a97fe76712b..b58299e49c23 100644 > --- a/fs/f2fs/segment.c > +++ b/fs/f2fs/segment.c > @@ -454,6 +454,20 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need) > io_schedule(); > finish_wait(&sbi->gc_thread->fggc_wq, &wait); > } else { > + > + /* > + * Before triggering foreground GC, submit all cached DATA > + * write bios. During writeback, pages may be added to > + * write_io[DATA].bio with PG_writeback set but the bio not > + * yet submitted. If GC's move_data_page() blocks on > + * __folio_lock() for such a folio, and the lock holder waits > + * for PG_writeback to clear via VFS folio_wait_writeback() > + * neither thread can make progress. Flushing here ensures > + * the bio completion callback can clear PG_writeback. > + */ > + > + f2fs_submit_merged_write(sbi, DATA); > + > struct f2fs_gc_control gc_control = { > .victim_segno = NULL_SEGNO, > .init_gc_type = f2fs_sb_has_blkzoned(sbi) ? Hi  jaegeuk, chao Gentle ping on this patch. Could you please take a look when you have time? If there are any issues with the patch, I'm happy to address them in a new version. Thanks