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

[Joseph Qi <joseph.qi@linux.alibaba.com>]

On 2025/10/9 23:49, Deepanshu Kartikey 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 defragmented, causing subsequent operations to see outdated extent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@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>

Looks fine.
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.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 +		 * stale cached data with outdated extent flags.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: