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Message-ID: <20251009154903.522339-1-kartikey406@gmail.com>
Date: Thu, 9 Oct 2025 21:19:03 +0530
From: Deepanshu Kartikey <kartikey406@...il.com>
To: mark@...heh.com,
jlbec@...lplan.org,
joseph.qi@...ux.alibaba.com
Cc: ocfs2-devel@...ts.linux.dev,
linux-kernel@...r.kernel.org,
Deepanshu Kartikey <kartikey406@...il.com>,
syzbot+6fdd8fa3380730a4b22c@...kaller.appspotmail.com
Subject: [PATCH v2] ocfs2: clear extent cache after moving/defragmenting extents
The extent map cache can become stale when extents are moved or
defragmented, causing subsequent operations to see outdated extent
flags. This triggers a BUG_ON in ocfs2_refcount_cal_cow_clusters().
The problem occurs when:
1. copy_file_range() creates a reflinked extent with OCFS2_EXT_REFCOUNTED
2. ioctl(FITRIM) triggers ocfs2_move_extents()
3. __ocfs2_move_extents_range() reads and caches the extent (flags=0x2)
4. ocfs2_move_extent()/ocfs2_defrag_extent() calls __ocfs2_move_extent()
which clears OCFS2_EXT_REFCOUNTED flag on disk (flags=0x0)
5. The extent map cache is not invalidated after the move
6. Later write() operations read stale cached flags (0x2) but disk has
updated flags (0x0), causing a mismatch
7. BUG_ON(!(rec->e_flags & OCFS2_EXT_REFCOUNTED)) triggers
Fix by clearing the extent map cache after each extent move/defrag
operation in __ocfs2_move_extents_range(). This ensures subsequent
operations read fresh extent data from disk.
Link: https://lore.kernel.org/all/20251009142917.517229-1-kartikey406@gmail.com/T/
Reported-by: syzbot+6fdd8fa3380730a4b22c@...kaller.appspotmail.com
Tested-by: syzbot+6fdd8fa3380730a4b22c@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?id=2959889e1f6e216585ce522f7e8bc002b46ad9e7
Signed-off-by: Deepanshu Kartikey <kartikey406@...il.com>
---
Changes in v2:
- Fix moved to __ocfs2_move_extents_range() instead of ocfs2_refcount_cow()
- The real issue is in FITRIM/move_extents code path, not COW path
- COW path already clears cache at end of ocfs2_refcount_cow_hunk()
fs/ocfs2/move_extents.c | 5 +++++
1 file changed, 5 insertions(+)
---
fs/ocfs2/move_extents.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/fs/ocfs2/move_extents.c b/fs/ocfs2/move_extents.c
index 86f2631e6360..10923bf7c8b8 100644
--- a/fs/ocfs2/move_extents.c
+++ b/fs/ocfs2/move_extents.c
@@ -867,6 +867,11 @@ static int __ocfs2_move_extents_range(struct buffer_head *di_bh,
mlog_errno(ret);
goto out;
}
+ /*
+ * Invalidate extent cache after moving/defragging to prevent
+ * stale cached data with outdated extent flags.
+ */
+ ocfs2_extent_map_trunc(inode, cpos);
context->clusters_moved += alloc_size;
next:
--
2.43.0
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