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

[Mark Fasheh]

On Thu, Oct 9, 2025 at 8:49 AM Deepanshu Kartikey <kartikey406@xxxxxxxxx> wrote:
>
> 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 defragmented, causing subsequent operations to see outdated extent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@xxxxxxxxx/T/
> Reported-by: syzbot+6fdd8fa3380730a4b22c@xxxxxxxxxxxxxxxxxxxxxxxxx
> Tested-by: syzbot+6fdd8fa3380730a4b22c@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?id=2959889e1f6e216585ce522f7e8bc002b46ad9e7
> Signed-off-by: Deepanshu Kartikey <kartikey406@xxxxxxxxx>

Reviewed-by: Mark Fasheh <mark@xxxxxxxxxx>