* [PATCH] f2fs: fix potential deadlock in f2fs_balance_fs()
@ 2026-03-25 13:37 ruipengqi
2026-04-20 1:41 ` Ruipeng Qi
2026-04-20 7:35 ` Chao Yu
0 siblings, 2 replies; 3+ messages in thread
From: ruipengqi @ 2026-03-25 13:37 UTC (permalink / raw)
To: jaegeuk; +Cc: chao, linux-f2fs-devel, linux-kernel, Ruipeng Qi
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 //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 <ruipengqi3@gmail.com>
---
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) ?
--
2.25.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] f2fs: fix potential deadlock in f2fs_balance_fs()
2026-03-25 13:37 [PATCH] f2fs: fix potential deadlock in f2fs_balance_fs() ruipengqi
@ 2026-04-20 1:41 ` Ruipeng Qi
2026-04-20 7:35 ` Chao Yu
1 sibling, 0 replies; 3+ messages in thread
From: Ruipeng Qi @ 2026-04-20 1:41 UTC (permalink / raw)
To: jaegeuk; +Cc: chao, linux-f2fs-devel, linux-kernel
On 2026/3/25 21:37, 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 //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<ruipengqi3@gmail.com>
> ---
> 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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] f2fs: fix potential deadlock in f2fs_balance_fs()
2026-03-25 13:37 [PATCH] f2fs: fix potential deadlock in f2fs_balance_fs() ruipengqi
2026-04-20 1:41 ` Ruipeng Qi
@ 2026-04-20 7:35 ` Chao Yu
1 sibling, 0 replies; 3+ messages in thread
From: Chao Yu @ 2026-04-20 7:35 UTC (permalink / raw)
To: ruipengqi, jaegeuk; +Cc: chao, linux-f2fs-devel, linux-kernel
Hi Ruipeng,
Sorry, I missed your patch.
On 3/25/2026 9:37 PM, 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 //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 <ruipengqi3@gmail.com>
> ---
> 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);
Do we need to call f2fs_submit_merged_ipu_write(sbi, bio, NULL) to commit
cached IPU folios as well?
Not sure, this race condition will happen for node folio.
Thanks,
> +
> struct f2fs_gc_control gc_control = {
> .victim_segno = NULL_SEGNO,
> .init_gc_type = f2fs_sb_has_blkzoned(sbi) ?
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2026-04-20 7:35 UTC | newest]
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2026-03-25 13:37 [PATCH] f2fs: fix potential deadlock in f2fs_balance_fs() ruipengqi
2026-04-20 1:41 ` Ruipeng Qi
2026-04-20 7:35 ` Chao Yu
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