* Re: [PATCH v3] f2fs: fix potential deadlock in f2fs_balance_fs()
[not found] ` <e4b82e9f-c863-4d3a-8077-b56df9faa491@kernel.org>
@ 2026-05-10 12:10 ` Ruipeng Qi
0 siblings, 0 replies; 2+ messages in thread
From: Ruipeng Qi @ 2026-05-10 12:10 UTC (permalink / raw)
To: Chao Yu, jaegeuk; +Cc: linux-f2fs-devel, linux-kernel
On 5/3/2026 5:47 PM, Chao Yu wrote:
> On 5/2/26 20:41, ruipengqi wrote:
>> From: Ruipeng Qi <ruipengqi3@gmail.com>
>>
>> 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@kernel.org>
>
> Chao Yu <chao@kernel.org>, :)
>
>> Signed-off-by: Ruipeng Qi <ruipengqi3@gmail.com>
>
> Reviewed-by: Chao Yu <chao@kernel.org>
>
> Thanks,
Hi Jaegeuk, Chao,
Gentle ping.
This patch has been discussed for about a month and
already got Reviewed-by from Chao.
Could you please pick up this patch when you have time?
Thanks,
Ruipeng
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