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

[Daeho Jeong]

On Wed, Mar 11, 2026 at 6:44 AM Chao Yu <chao@xxxxxxxxxx> wrote:
>
> On 2026/3/11 01:54, Daeho Jeong wrote:
> > From: Daeho Jeong <daehojeong@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > ---
> >   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?

Oh, AT_SSR needs to select the free section in this case?
I am confused. Why do we need the below logic?
Looks like WA for the AT_SSR case?

In f2fs_get_section_mtime()
out:
        if (unlikely(mtime == INVALID_MTIME))
                mtime -= 1;
        return mtime;


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