Re: [f2fs-dev] [PATCH] f2fs: fix to skip empty sections in f2fs_get_victim

[Chao Yu <chao@kernel.org>]

On 2026/3/11 01:54, Daeho Jeong wrote:
> From: Daeho Jeong <daehojeong@google.com>
> 
> In age-based victim selection (ATGC, AT_SSR, or GC_CB), f2fs_get_victim
> can encounter sections with zero valid blocks. This situation often
> arises when checkpoint is disabled or due to race conditions between
> SIT updates and dirty list management.
> 
> In such cases, f2fs_get_section_mtime() returns INVALID_MTIME, which
> subsequently triggers a fatal f2fs_bug_on(sbi, mtime == INVALID_MTIME)
> in add_victim_entry() or get_cb_cost().
> 
> This patch adds a check in f2fs_get_victim's selection loop to skip
> sections with no valid blocks. This prevents unnecessary age
> calculations for empty sections and avoids the associated kernel panic.
> This change also allows removing redundant checks in add_victim_entry().
> 
> Signed-off-by: Daeho Jeong <daehojeong@google.com>
> ---
>   fs/f2fs/gc.c | 9 +++------
>   1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index 2e0f67946914..981eac629fe9 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -521,12 +521,6 @@ static void add_victim_entry(struct f2fs_sb_info *sbi,
>   	struct sit_info *sit_i = SIT_I(sbi);
>   	unsigned long long mtime = 0;
>   
> -	if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED))) {
> -		if (p->gc_mode == GC_AT &&
> -			get_valid_blocks(sbi, segno, true) == 0)
> -			return;
> -	}
> -
>   	mtime = f2fs_get_section_mtime(sbi, segno);
>   	f2fs_bug_on(sbi, mtime == INVALID_MTIME);
>   
> @@ -889,6 +883,9 @@ int f2fs_get_victim(struct f2fs_sb_info *sbi, unsigned int *result,
>   		if (sec_usage_check(sbi, secno))
>   			goto next;
>   
> +		if (!get_valid_blocks(sbi, segno, true))
> +			goto next;

Well, for f2fs_get_victim(, AT_SSR), once there are no dirty segment, if we
don't count free segment as candidates, then, we can not find any valid victim?

Thanks,

> +
>   		/* Don't touch checkpointed data */
>   		if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED))) {
>   			if (p.alloc_mode == LFS) {