Re: [f2fs-dev] [PATCH 1/2] f2fs: fix wrong extent_info data for precache extents

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

On 9/12/2025 11:36 AM, wangzijie wrote:
>> On 9/11/2025 5:07 PM, wangzijie wrote:
>>>> On 9/10/25 21:58, wangzijie wrote:
>>>>> When the data layout is like this:
>>>>> dnode1:                     dnode2:
>>>>> [0]      A                  [0]    NEW_ADDR
>>>>> [1]      A+1                [1]    0x0
>>>>> ...                         ....
>>>>> [1016]   A+1016
>>>>> [1017]   B (B!=A+1017)      [1017] 0x0
>>>>>
>>>>> We can build this kind of layout by following steps(with i_extra_isize:36):
>>>>> ./f2fs_io write 1 0 1881 rand dsync testfile
>>>>> ./f2fs_io write 1 1881 1 rand buffered testfile
>>>>> ./f2fs_io fallocate 0 7708672 4096 testfile
>>>>>
>>>>> And when we map first data block in dnode2, we will get wrong extent_info data:
>>>>> map->m_len = 1
>>>>> ofs = start_pgofs - map->m_lblk = 1882 - 1881 = 1
>>>>>
>>>>> ei.fofs = start_pgofs = 1882
>>>>> ei.len = map->m_len - ofs = 1 - 1 = 0
>>>>>
>>>>> Fix it by skipping updating this kind of extent info.
>>>>>
>>>>> Signed-off-by: wangzijie <wangzijie1@honor.com>
>>>>> ---
>>>>>    fs/f2fs/data.c | 3 +++
>>>>>    1 file changed, 3 insertions(+)
>>>>>
>>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>>>> index 7961e0ddf..b8bb71852 100644
>>>>> --- a/fs/f2fs/data.c
>>>>> +++ b/fs/f2fs/data.c
>>>>> @@ -1649,6 +1649,9 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map, int flag)
>>>>>    
>>>>>    		switch (flag) {
>>>>>    		case F2FS_GET_BLOCK_PRECACHE:
>>>>> +			if (__is_valid_data_blkaddr(map->m_pblk) &&
>>>>> +				start_pgofs - map->m_lblk == map->m_len)
>>>>> +				map->m_flags &= ~F2FS_MAP_MAPPED;
>>>>
>>>> It looks we missed to reset value for map variable in f2fs_precache_extents(),
>>>> what do you think of this?
>>>>
>>>> ---
>>>>    fs/f2fs/file.c | 4 +++-
>>>>    1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>>> index 1aae4361d0a8..2b14151d4130 100644
>>>> --- a/fs/f2fs/file.c
>>>> +++ b/fs/f2fs/file.c
>>>> @@ -3599,7 +3599,7 @@ static int f2fs_ioc_io_prio(struct file *filp, unsigned long arg)
>>>>    int f2fs_precache_extents(struct inode *inode)
>>>>    {
>>>>    	struct f2fs_inode_info *fi = F2FS_I(inode);
>>>> -	struct f2fs_map_blocks map;
>>>> +	struct f2fs_map_blocks map = { 0 };
>>>>    	pgoff_t m_next_extent;
>>>>    	loff_t end;
>>>>    	int err;
>>>> @@ -3617,6 +3617,8 @@ int f2fs_precache_extents(struct inode *inode)
>>>>
>>>>    	while (map.m_lblk < end) {
>>>>    		map.m_len = end - map.m_lblk;
>>>> +		map.m_pblk = 0;
>>>> +		map.m_flags = 0;
>>>>
>>>>    		f2fs_down_write(&fi->i_gc_rwsem[WRITE]);
>>>>    		err = f2fs_map_blocks(inode, &map, F2FS_GET_BLOCK_PRECACHE);
>>>> -- 
>>>> 2.49.0
>>>>
>>>> Thanks,
>>>>
>>>>>    			goto sync_out;
>>>>>    		case F2FS_GET_BLOCK_BMAP:
>>>>>    			map->m_pblk = 0;
>>>
>>>
>>> We have already reset m_flags (map->m_flags = 0) in f2fs_map_blocks().
>>
>> Zijie:
>>
>> Oops, that's right, thanks for correcting me.
>>
>>>
>>> I think that this bug is caused by we missed to reset m_flags when we
>>> goto next_dnode in below case：
>>>
>>> Data layout is something like this:
>>> dnode1:                     dnode2:
>>> [0]      A                  [0]    NEW_ADDR
>>> [1]      A+1                [1]    0x0
>>> ...
>>> [1016]   A+1016
>>> [1017]   B (B!=A+1017)      [1017] 0x0
>>>
>>> we map the last block(valid blkaddr) in dnode1:
>>> map->m_flags |= F2FS_MAP_MAPPED;
>>> map->m_pblk = blkaddr(valid blkaddr);
>>> map->m_len = 1;
>>> then we goto next_dnode, meet the first block in dnode2(hole), goto sync_out:
>>> map->m_flags & F2FS_MAP_MAPPED == true, and we make wrong blkaddr/len for extent_info.
>>
>> So, can you please add above explanation into commit message? that
>> should be helpful for understanding the problem more clearly.
>>
>> Please take a look at this case w/ your patch:
>>
>> mkfs.f2fs -O extra_attr,compression /dev/vdb -f
>> mount /dev/vdb /mnt/f2fs -o mode=lfs
>> cd /mnt/f2fs
>> f2fs_io write 1 0 1883 rand dsync testfile
>> f2fs_io fallocate 0 7712768 4096 testfile
>> f2fs_io write 1 1881 1 rand buffered testfile
>> xfs_io testfile -c "fsync"
>> cd /
>> umount /mnt/f2fs
>> mount /dev/vdb /mnt/f2fs
>> f2fs_io precache_extents /mnt/f2fs/testfile
>> umount /mnt/f2fs
>>
>>           f2fs_io-733     [010] .....    78.134136: f2fs_update_read_extent_tree_range: dev = (253,16), ino = 4, pgofs = 1882, len = 0, blkaddr = 17410, c_len = 0
>>
>> I suspect we need this?
>>
>> @@ -1784,7 +1781,8 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map, int flag)
>>          }
>>
>>          if (flag == F2FS_GET_BLOCK_PRECACHE) {
>> -               if (map->m_flags & F2FS_MAP_MAPPED) {
>> +               if ((map->m_flags & F2FS_MAP_MAPPED) &&
>> +                       (map->m_len - ofs)) {
>>                          unsigned int ofs = start_pgofs - map->m_lblk;
>>
>>                          f2fs_update_read_extent_cache_range(&dn,
> 
> Thanks for pointing out this. Let me find a way to cover these cases and do more test.
> 
>> BTW, I find another bug, if one blkaddr is adjcent to previous extent,
>> but and it is valid, we need to set m_next_extent to pgofs rather than
>> pgofs + 1.
>>
>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>> index cbf8841642c7..ac88ed68059c 100644
>> --- a/fs/f2fs/data.c
>> +++ b/fs/f2fs/data.c
>> @@ -1789,8 +1789,11 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map, int flag)
>>                                  start_pgofs, map->m_pblk + ofs,
>>                                  map->m_len - ofs);
>>                  }
>> -               if (map->m_next_extent)
>> -                       *map->m_next_extent = pgofs + 1;
>> +               if (map->m_next_extent) {
>> +                       *map->m_next_extent = pgofs;
>> +                       if (!__is_valid_data_blkaddr(blkaddr))
>> +                               *map->m_next_extent += 1;
>> +               }
>>          }
>>          f2fs_put_dnode(&dn);
> 
> Maybe it can be this?
> if (map->m_next_extent)
> 	*map->m_next_extent = is_hole ? pgofs + 1 : pgofs;

It's better, will update, thank you. :)

Thanks,




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