linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: fix to avoid migrating empty section

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Message-ID: <CAHJ8P3+BAzDzW9GixwgXBs6NJqWm+pAUe4cCyhNKWwUx+5f+hQ@mail.gmail.com>
Date: Wed, 3 Sep 2025 09:56:23 +0800
From: Zhiguo Niu <niuzhiguo84@...il.com>
To: Chao Yu <chao@...nel.org>
Cc: jaegeuk@...nel.org, Daeho Jeong <daehojeong@...gle.com>, linux-kernel@...r.kernel.org, 
	linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: fix to avoid migrating empty section

Chao Yu <chao@...nel.org> 于2025年9月3日周三 09:33写道：
>
> On 9/3/25 08:04, Zhiguo Niu wrote:
> > Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@...ts.sourceforge.net>
> > 于2025年9月1日周一 10:08写道：
> >>
> >> It reports a bug from device w/ zufs:
> >>
> >> F2FS-fs (dm-64): Inconsistent segment (173822) type [1, 0] in SSA and SIT
> >> F2FS-fs (dm-64): Stopped filesystem due to reason: 4
> >>
> >> Thread A                                Thread B
> >> - f2fs_expand_inode_data
> >>  - f2fs_allocate_pinning_section
> >>   - f2fs_gc_range
> >>    - do_garbage_collect w/ segno #x
> >>                                         - writepage
> >>                                          - f2fs_allocate_data_block
> >>                                           - new_curseg
> >>                                            - allocate segno #x
> >>
> >> The root cause is: fallocate on pinning file may race w/ block allocation
> >> as above, result in do_garbage_collect() from fallocate() may migrate
> >> segment which is just allocated by a log, the log will update segment type
> >> in its in-memory structure, however GC will get segment type from on-disk
> >> SSA block, once segment type changes by log, we can detect such
> >> inconsistency, then shutdown filesystem.
> >>
> >> In this case, on-disk SSA shows type of segno #173822 is 1 (SUM_TYPE_NODE),
> >> however segno #173822 was just allocated as data type segment, so in-memory
> >> SIT shows type of segno #173822 is 0 (SUM_TYPE_DATA).
> >>
> >> Change as below to fix this issue:
> >> - check whether current section is empty before gc
> >> - add sanity checks on do_garbage_collect() to avoid any race case, result
> >> in migrating segment used by log.
> >> - btw, it fixes misc issue in printed logs: "SSA and SIT" -> "SIT and SSA".
> >>
> >> Fixes: 9703d69d9d15 ("f2fs: support file pinning for zoned devices")
> >> Cc: Daeho Jeong <daehojeong@...gle.com>
> >> Signed-off-by: Chao Yu <chao@...nel.org>
> >> ---
> >>  fs/f2fs/gc.c | 16 +++++++++++++++-
> >>  1 file changed, 15 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> >> index ed3acbfc83ca..a7708cf80c04 100644
> >> --- a/fs/f2fs/gc.c
> >> +++ b/fs/f2fs/gc.c
> >> @@ -1794,6 +1794,13 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
> >>                 struct folio *sum_folio = filemap_get_folio(META_MAPPING(sbi),
> >>                                         GET_SUM_BLOCK(sbi, segno));
> >>
> >> +               if (is_cursec(sbi, GET_SEC_FROM_SEG(sbi, segno))) {
> >> +                       f2fs_err(sbi, "%s: segment %u is used by log",
> >> +                                                       __func__, segno);
> >> +                       f2fs_bug_on(sbi, 1);
> > Hi Chao,
> > Do we need f2fs_bug_on here?  or it is enough to skip current segno
> > and let gc continue?
>
> Zhiguo,
>
> I think we should never select in-use segment as GC victim, so I add a
> f2fs_bug_on() here to detect any potential bugs. Let's see what will we
> find w/ this.
Hi Chao,
Got it and thanks for this.
>
> Thanks,
>
> > Thanks!
> >> +                       goto skip;
> >> +               }
> >> +
> >>                 if (get_valid_blocks(sbi, segno, false) == 0)
> >>                         goto freed;
> >>                 if (gc_type == BG_GC && __is_large_section(sbi) &&
> >> @@ -1805,7 +1812,7 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
> >>
> >>                 sum = folio_address(sum_folio);
> >>                 if (type != GET_SUM_TYPE((&sum->footer))) {
> >> -                       f2fs_err(sbi, "Inconsistent segment (%u) type [%d, %d] in SSA and SIT",
> >> +                       f2fs_err(sbi, "Inconsistent segment (%u) type [%d, %d] in SIT and SSA",
> >>                                  segno, type, GET_SUM_TYPE((&sum->footer)));
> >>                         f2fs_stop_checkpoint(sbi, false,
> >>                                 STOP_CP_REASON_CORRUPTED_SUMMARY);
> >> @@ -2068,6 +2075,13 @@ int f2fs_gc_range(struct f2fs_sb_info *sbi,
> >>                         .iroot = RADIX_TREE_INIT(gc_list.iroot, GFP_NOFS),
> >>                 };
> >>
> >> +               /*
> >> +                * avoid migrating empty section, as it can be allocated by
> >> +                * log in parallel.
> >> +                */
> >> +               if (!get_valid_blocks(sbi, segno, true))
> >> +                       continue;
> >> +
> >>                 if (is_cursec(sbi, GET_SEC_FROM_SEG(sbi, segno)))
> >>                         continue;
> >>
> >> --
> >> 2.49.0
> >>
> >>
> >>
> >> _______________________________________________
> >> Linux-f2fs-devel mailing list
> >> Linux-f2fs-devel@...ts.sourceforge.net
> >> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>