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

Jaegeuk Kim
2025-04-04T19:55:55Z

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;
+
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