From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DB18723EA9B for ; Sun, 3 May 2026 09:48:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777801683; cv=none; b=YJ3degJGEy4qRqlPVLUUoOdsz/ztBTRPuuoy1jEc92fBbbb57JNpfVvQv54ML/1jIkhMS4jl842sDywEFEmL6LHQuFD+FlqdKjvWaNGMfWop9prAGDgQMIFS/HTvt9K9HcF29ViWKhECNA5VjPNng+yTGxMJkMNfeMsRDMPFLIo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777801683; c=relaxed/simple; bh=jCP1aZfbeEXQHCOMtZHbDHupbSzcuxXLiYWGTo4+nk0=; h=Message-ID:Date:MIME-Version:Cc:Subject:To:References:From: In-Reply-To:Content-Type; b=Z8jEOSuRUdyUxxJX87aoGvaSSnhFmvend2vbJivK0pQnOFs/p9ePuLe1cNvFnz+1mTcQDVwt78LSLC70f9ltTuSPvsRPJDfURIDX6r7OJ4IRhGcO8mIaVVmZWrxFOz2ul2VSNgnCam4hLXVTOuD+YzUQxOAXF0TxVOhzTKkpI9s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VmMcOGTm; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="VmMcOGTm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 44597C2BCB4; Sun, 3 May 2026 09:48:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777801683; bh=jCP1aZfbeEXQHCOMtZHbDHupbSzcuxXLiYWGTo4+nk0=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=VmMcOGTmI5S14RrW0zIBS31AkAtW2ZwllZtnhEVHSh6uFzaue5+hv+ciiOphQHjJE dP4EPeTNZ1w3VVB3SbdHPd2/bcfXN4AZyaiAIhqYbxDbE1Iwy0lF5J9Qqxel9YhvUO vZyVzJnFge9pMltWw/gQ9JRjVPuitecQrob1jWo4UpUm1PHKGt6oFA6/05cxXIVYse Y5OuRb2Xh/X4lesy0Xan9apr/lVPkNxOKb6szMes8ugECR6HwtOmIYdqwBU1gZmg6r NDvZVhXsb5r2U2AfeguKAv9IOTynYq1aDWDopAwpt3jaPcXnNzBt/CFoA6FASW/5kM MtUrHsvWYZIeg== Message-ID: Date: Sun, 3 May 2026 17:47:59 +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 Cc: chao@kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] f2fs: fix potential deadlock in f2fs_balance_fs() To: ruipengqi , jaegeuk@kernel.org References: <20260502124157.3406780-1-ruipengqi3@gmail.com> Content-Language: en-US From: Chao Yu In-Reply-To: <20260502124157.3406780-1-ruipengqi3@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 5/2/26 20:41, 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 > 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. > > OPU/IPU DATA folio are all affected by this issue. To avoid such > potential deadlocks, always commit these cached folios before > triggering f2fs_gc() in f2fs_balance_fs(). > > v2: > - Commit cached OPU/IPU folios, not just OPU folios as in v1. > > v3: > - Fixed minor grammatical issues > - Add comment on lockless list_empty() to explain why it is safe > without holding bio_list_lock > > Suggested-by: Chao Chao Yu , :) > Signed-off-by: Ruipeng Qi Reviewed-by: Chao Yu Thanks,