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

[wangzijie <wangzijie1@honor.com>]

>On 9/12/2025 6:06 PM, wangzijie wrote:
>>> 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,
>> 
>> Hi Chao,
>> I test some cases with this change:
>> 
>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>> index 7961e0ddf..7093fdc95 100644
>> --- a/fs/f2fs/data.c
>> +++ b/fs/f2fs/data.c
>> @@ -1777,13 +1777,13 @@ 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) {
>>                          unsigned int ofs = start_pgofs - map->m_lblk;
>> -
>> -                       f2fs_update_read_extent_cache_range(&dn,
>> -                               start_pgofs, map->m_pblk + ofs,
>> -                               map->m_len - ofs);
>> +                       if (map->m_len - ofs > 0)
>> +                               f2fs_update_read_extent_cache_range(&dn,
>> +                                       start_pgofs, map->m_pblk + ofs,
>> +                                       map->m_len - ofs);
>>                  }
>>                  if (map->m_next_extent)
>> -                       *map->m_next_extent = pgofs + 1;
>> +                       *map->m_next_extent = is_hole ? pgofs + 1 : pgofs;
>>          }
>>          f2fs_put_dnode(&dn);
>>   unlock_out:
>> 
>> 
>> test cases:
>> 
>> case1:
>> dnode1:                     dnode2:
>> [0]      A                  [0]    NEW_ADDR
>> [1]      A+1                [1]    0x0
>> ...                         ....
>> [1016]   A+1016
>> [1017]   B (B!=A+1017)      [1017] 0x0
>> 
>> case2:
>> dnode1:                     dnode2:
>> [0]      A                  [0]    C (C!=B+1)
>> [1]      A+1                [1]    C+1
>> ...                         ....
>> [1016]   A+1016
>> [1017]   B (B!=A+1017)      [1017] 0x0
>> 
>> case3:
>> dnode1:                     dnode2:
>> [0]      A                  [0]    C (C!=B+2)
>> [1]      A+1                [1]    C+1
>> ...                         ....
>> [1015]   A+1015
>> [1016]   B (B!=A+1016)
>> [1017]   B+1                [1017] 0x0
>> 
>> case4:
>> one blkaddr is adjcent to previous extent, and it is valid.
> > > And from the result, it seems this change can cover these
>> situations correctly.
>> Do we need a patch with this change?
>
>Zijie, thanks for the test.
>
>IMO, we'd better use these changes:
>
>-
>-                       f2fs_update_read_extent_cache_range(&dn,
>-                               start_pgofs, map->m_pblk + ofs,
>-                               map->m_len - ofs);
>+                       if (map->m_len - ofs > 0)
>+                               f2fs_update_read_extent_cache_range(&dn,
>+                                       start_pgofs, map->m_pblk + ofs,
>+                                       map->m_len - ofs);
>
>instead of
>
>    		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;
>
>Can you please rebase your patchset on mine and send v2?
>
>https://lore.kernel.org/linux-f2fs-devel/20250912081250.44383-1-chao@kernel.org
>
>BTW, please add fixes line in your patch.
>
>Thanks,

OK, I will correct this part and follow your suggestion. Thank you.


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