Re: [PATCH v5] f2fs: prevent the current section from being selected as a victim during GC

Chao Yu
2025-04-07T02:11:13Z

On 4/7/25 10:08, Chao Yu wrote:
> On 4/5/25 03:55, Jaegeuk Kim wrote:
>> Hi Yohan,
>>
>> I modified this patch after applying the clean up by
>>
>> https://lore.kernel.org/linux-f2fs-devel/20250404195442.413945-1-jaegeuk@kernel.org/T/#u
>>
>> --- a/fs/f2fs/segment.h
>> +++ b/fs/f2fs/segment.h
>> @@ -486,6 +486,11 @@ static inline void __set_test_and_free(struct f2fs_sb_info *sbi,
>>
>> free_i->free_sections++;
>>
>> + if (GET_SEC_FROM_SEG(sbi, sbi->next_victim_seg[BG_GC]) == secno)
>> + sbi->next_victim_seg[BG_GC] = NULL_SEGNO;
>> + if (GET_SEC_FROM_SEG(sbi, sbi->next_victim_seg[FG_GC]) == secno)
>> + sbi->next_victim_seg[FG_GC] = NULL_SEGNO;
>
> Reviewed-by: Chao Yu <chao@kernel.org>

Oh, can we add Fixes line to make it to be merged into stable kernel?

Thanks,

>
> Thanks,
>
>> +
>> unlock_out:
>> spin_unlock(&free_i->segmap_lock);
>> }
>>
>> On 04/04, yohan.joung wrote:
>>> When selecting a victim using next_victim_seg in a large section, the
>>> selected section might already have been cleared and designated as the
>>> new current section, making it actively in use.
>>> This behavior causes inconsistency between the SIT and SSA.
>>>
>>> F2FS-fs (dm-54): Inconsistent segment (70961) type [0, 1] in SSA and SIT
>>> Call trace:
>>> dump_backtrace+0xe8/0x10c
>>> show_stack+0x18/0x28
>>> dump_stack_lvl+0x50/0x6c
>>> dump_stack+0x18/0x28
>>> f2fs_stop_checkpoint+0x1c/0x3c
>>> do_garbage_collect+0x41c/0x271c
>>> f2fs_gc+0x27c/0x828
>>> gc_thread_func+0x290/0x88c
>>> kthread+0x11c/0x164
>>> ret_from_fork+0x10/0x20
>>>
>>> issue scenario
>>> segs_per_sec=2
>>> - seg#0 and seg#1 are all dirty
>>> - all valid blocks are removed in seg#1
>>> - gc select this sec and next_victim_seg=seg#0
>>> - migrate seg#0, next_victim_seg=seg#1
>>> - checkpoint -> sec(seg#0, seg#1) becomes free
>>> - allocator assigns sec(seg#0, seg#1) to curseg
>>> - gc tries to migrate seg#1
>>>
>>> Signed-off-by: yohan.joung <yohan.joung@sk.com>
>>> Signed-off-by: Chao Yu <chao@kernel.org>
>>> ---
>>> fs/f2fs/segment.h | 9 ++++++++-
>>> 1 file changed, 8 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
>>> index 0465dc00b349..0773283babfa 100644
>>> --- a/fs/f2fs/segment.h
>>> +++ b/fs/f2fs/segment.h
>>> @@ -474,8 +474,15 @@ static inline void __set_test_and_free(struct f2fs_sb_info *sbi,
>>> next = find_next_bit(free_i->free_segmap,
>>> start_segno + SEGS_PER_SEC(sbi), start_segno);
>>> if (next >= start_segno + usable_segs) {
>>> - if (test_and_clear_bit(secno, free_i->free_secmap))
>>> + if (test_and_clear_bit(secno, free_i->free_secmap)) {
>>> free_i->free_sections++;
>>> +
>>> + if (GET_SEC_FROM_SEG(sbi, sbi->next_victim_seg[BG_GC]) == secno)
>>> + sbi->next_victim_seg[BG_GC] = NULL_SEGNO;
>>> +
>>> + if (GET_SEC_FROM_SEG(sbi, sbi->next_victim_seg[FG_GC]) == secno)
>>> + sbi->next_victim_seg[FG_GC] = NULL_SEGNO;
>>> + }
>>> }
>>> }
>>> skip_free:
>>> --
>>> 2.33.0
>