[f2fs-dev] [PATCH 6.6.y] f2fs: fix to avoid migrating empty section

[f2fs-dev] [PATCH 6.6.y] f2fs: fix to avoid migrating empty section

[Robert Garcia]

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>
---
 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 8122135bb1ff..816a5aa263e6 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -1742,6 +1742,13 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
 					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) &&
@@ -1752,7 +1759,7 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
 
 		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)));
 			set_sbi_flag(sbi, SBI_NEED_FSCK);
 			f2fs_stop_checkpoint(sbi, false,
@@ -2005,6 +2012,13 @@ 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;
+
 		do_garbage_collect(sbi, segno, &gc_list, FG_GC,
 						dry_run_sections == 0);
 		put_gc_inode(&gc_list);
-- 
2.34.1



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[f2fs-dev] Patch "f2fs: fix to avoid migrating empty section" has been added to the 6.6-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    f2fs: fix to avoid migrating empty section

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     f2fs-fix-to-avoid-migrating-empty-section.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From stable+bounces-223511-greg=kroah.com@vger.kernel.org Mon Mar  9 09:33:17 2026
From: Robert Garcia <rob_garcia@163.com>
Date: Mon,  9 Mar 2026 16:32:27 +0800
Subject: f2fs: fix to avoid migrating empty section
To: stable@vger.kernel.org, Chao Yu <chao@kernel.org>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>, Daeho Jeong <daehojeong@google.com>, Robert Garcia <rob_garcia@163.com>, linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org
Message-ID: <20260309083227.3241109-1-rob_garcia@163.com>

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
@@ -1742,6 +1742,13 @@ 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) &&
@@ -1752,7 +1759,7 @@ 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)));
 			set_sbi_flag(sbi, SBI_NEED_FSCK);
 			f2fs_stop_checkpoint(sbi, false,
@@ -2005,6 +2012,13 @@ 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;
+
 		do_garbage_collect(sbi, segno, &gc_list, FG_GC,
 						dry_run_sections == 0);
 		put_gc_inode(&gc_list);


Patches currently in stable-queue which might be from rob_garcia@163.com are

queue-6.6/f2fs-fix-to-avoid-migrating-empty-section.patch


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