On 5/23/25 09:39, Zhiguo Niu wrote:
> Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>
> 于2025年5月21日周三 20:02写道：
>>
>> INFO: task syz-executor328:5856 blocked for more than 144 seconds.
>> Not tainted 6.15.0-rc6-syzkaller-00208-g3c21441eeffc #0
>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> task:syz-executor328 state:D stack:24392 pid:5856 tgid:5832 ppid:5826
>> task_flags:0x400040 flags:0x00004006
>> Call Trace:
>> <TASK>
>> context_switch kernel/sched/core.c:5382 [inline]
>> __schedule+0x168f/0x4c70 kernel/sched/core.c:6767
>> __schedule_loop kernel/sched/core.c:6845 [inline]
>> schedule+0x165/0x360 kernel/sched/core.c:6860
>> io_schedule+0x81/0xe0 kernel/sched/core.c:7742
>> f2fs_balance_fs+0x4b4/0x780 fs/f2fs/segment.c:444
>> f2fs_map_blocks+0x3af1/0x43b0 fs/f2fs/data.c:1791
>> f2fs_expand_inode_data+0x653/0xaf0 fs/f2fs/file.c:1872
>> f2fs_fallocate+0x4f5/0x990 fs/f2fs/file.c:1975
>> vfs_fallocate+0x6a0/0x830 fs/open.c:338
>> ioctl_preallocate fs/ioctl.c:290 [inline]
>> file_ioctl fs/ioctl.c:-1 [inline]
>> do_vfs_ioctl+0x1b8f/0x1eb0 fs/ioctl.c:885
>> __do_sys_ioctl fs/ioctl.c:904 [inline]
>> __se_sys_ioctl+0x82/0x170 fs/ioctl.c:892
>> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>> do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
>> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>>
>> The root cause is after commit 84b5bb8bf0f6 ("f2fs: modify
>> f2fs_is_checkpoint_ready logic to allow more data to be written with the
>> CP disable"), we will get chance to allow f2fs_is_checkpoint_ready() to
>> return true once below conditions are all true:
>> 1. checkpoint is disabled
>> 2. there are not enough free segments
>> 3. there are enough free blocks
>>
>> Then it will cause f2fs_balance_fs() to trigger foreground GC.
>>
>> void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
>> ...
>> if (!f2fs_is_checkpoint_ready(sbi))
>> return;
>>
>> And it mounts f2fs image w/ gc_merge,checkpoint=disable, so below deadloop
>> will happen:
>>
>> - f2fs_do_shutdown - vfs_fallocate -
>> gc_thread_func
>> - file_start_write
>> - __sb_start_write(SB_FREEZE_WRITE)
>> - f2fs_fallocate
>> - f2fs_expand_inode_data
>> - f2fs_map_blocks
>> - f2fs_balance_fs
>> - prepare_to_wait
>> - wake_up(gc_wait_queue_head)
>> - io_schedule
>> - bdev_freeze
>> - freeze_super
>> - sb->s_writers.frozen = SB_FREEZE_WRITE;
>> - sb_wait_write(sb, SB_FREEZE_WRITE);
>> -
>> if (sbi->sb->s_writers.frozen >= SB_FREEZE_WRITE) continue;
>> :
>> cause deadloop
>>
>> This patch fix to add check condition in f2fs_balance_fs(), so that if
>> checkpoint is disabled, we will just skip trigger foreground GC to
>> avoid above deadloop issue.
>>
>> Reported-by: syzbot+aa5bb5f6860e08a60...@syzkaller.appspotmail.com
>> Closes:
>> https://lore.kernel.org/linux-f2fs-devel/682d743a.a00a0220.29bc26.0289....@google.com
>> Fixes: 84b5bb8bf0f6 ("f2fs: modify f2fs_is_checkpoint_ready logic to allow
>> more data to be written with the CP disable")
>> Cc: Qi Han <ha...@vivo.com>
>> Signed-off-by: Chao Yu <c...@kernel.org>
>> ---
>> v2:
>> - add missing Closes line
>> - fix to use git commit description style
>>
>> fs/f2fs/segment.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>> index 5ff0111ed974..19b716fda72a 100644
>> --- a/fs/f2fs/segment.c
>> +++ b/fs/f2fs/segment.c
>> @@ -433,6 +433,8 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
>> if (need && excess_cached_nats(sbi))
>> f2fs_balance_fs_bg(sbi, false);
>>
>> + if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED)))
>> + return;
>> if (!f2fs_is_checkpoint_ready(sbi))
>> return;
> Hi Chao,
> When I read this patch, I feel that it is somewhat redundant with the
> following checking about SBI_CP_DISABLED in f2fs_is_checkpoint_ready.
> Can we reorganize these checks for the f2fs_balance_fs case?
Zhiguo,
Oh, I agreed. I think we can just use is_sbi_flag_set(sbi, SBI_CP_DISABLED)
instead of f2fs_is_checkpoint_ready() here, let me revise it in v3.
- if (!f2fs_is_checkpoint_ready(sbi))
+ if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED)))
Thanks,
> This will make the code easier to read and understand.
> thanks!
>>
>> --
>> 2.49.0
>>
>>
>>
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