[PATCH v2] ocfs2: clear extent cache after moving/defragmenting extents

[Deepanshu Kartikey <kartikey406@gmail.com>]

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defragmented, causing subsequent operations to see outdated extent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@syzkaller.appspotmail.com
Tested-by: syzbot+6fdd8fa3380730a4b22c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?id=2959889e1f6e216585ce522f7e8bc002b46ad9e7
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.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+		 * stale cached data with outdated extent flags.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