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

[wangzijie <wangzijie1@honor.com>]

>>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?

Sorry, with this change, for case1:
The first block of dnode2 ([0]:NEW_ADDR) will be skipped.
Let me find a better way....


_______________________________________________
Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel