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

[Heming Zhao <heming.zhao@suse.com>]

Hi Joseph,

please check my comments in another mail.

https://lore.kernel.org/all/20251009142917.517229-1-kartikey406@gmail.com/T/#m0c02c884701c12d71206d0f9aba4450879b18e0c

- Heming

On 10/10/25 09:21, Joseph Qi wrote:
> 
> 
> 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 defragmented, causing subsequent operations to see outdated extent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:
> 
>