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

[wangzijie <wangzijie1@honor.com>]

>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;


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