[PATCH 6.12 288/460] f2fs: fix to avoid migrating empty section

Greg Kroah-Hartman
2026-03-23T14:44:44Z

6.12-stable review patch. If anyone has any objections, please let me know.

------------------

From: Chao Yu <chao@kernel.org>

[ Upstream commit d625a2b08c089397d3a03bff13fa8645e4ec7a01 ]

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@google.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
[ Use IS_CURSEC instead of is_cursec according to
commit c1cfc87e49525 ("f2fs: introduce is_cur{seg,sec}()"). ]
Signed-off-by: Robert Garcia <rob_garcia@163.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/f2fs/gc.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)

--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -1805,6 +1805,13 @@ static int do_garbage_collect(struct f2f
GET_SUM_BLOCK(sbi, segno));
f2fs_put_page(sum_page, 0);

+ 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);
+ goto skip;
+ }
+
if (get_valid_blocks(sbi, segno, false) == 0)
goto freed;
if (gc_type == BG_GC && __is_large_section(sbi) &&
@@ -1815,7 +1822,7 @@ static int do_garbage_collect(struct f2f

sum = page_address(sum_page);
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);
@@ -2079,6 +2086,13 @@ int f2fs_gc_range(struct f2fs_sb_info *s
.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;