Re: [f2fs-dev] [PATCH] f2fs: fix to avoid potential section-unaligned pinfile

[Chao Yu <chao@kernel.org>]

On 6/30/26 16:50, Zhiguo Niu wrote:
> Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>
> 于2026年6月29日周一 19:52写道：
>>
>> Blocks of pinfile may not aligned to section size due to wrong use
>> on pinfile, result in heavy overhead of GC, let avoid this by
>> adding additional check condition in f2fs_setattr().
>>
>> - truncate -s 8mb pinfile
>> : random checkpoint may persist filesize w/ inode
>> - fallocate -o 0 -l 8mb pinfile
>>  - f2fs_fallocate
>>   - f2fs_expand_inode_data
>>    - f2fs_allocate_pinning_section
>>    - f2fs_map_blocks
>>     - f2fs_map_lock
>>     - __allocate_data_block
>>     - file_need_truncate
>>     : w/ FADVISE_TRUNC_BIT, we can expect unaligned mapping can be
>>       truncated while open() if f2fs is not umount abnormally
>>     - f2fs_map_unlock
>>     : following f2fs checkpoint and sudden power-cut
>>
>> - mount
>> - open pinfile
>>  - f2fs_file_open
>>   - finish_preallocate_blocks
>>    - truncate_setsize
>>    : filesize is 8mb
>>    - f2fs_truncate
>>    : can only truncate block outside filesize, rather than truncating
>>      unaligned blocks inside filesize
> Hi Chao,
> 8MB is section alinged when fallocated by f2fs_allocate_pinning_section??
> so How could there are unaligned blocks inside filesize?

Zhiguo,

As partial blkaddrs were persisted and recovered, see comments around
f2fs_map_unlock().

>>
>> Fixes: f5a53edcf01e ("f2fs: support aligned pinned file")
>> Cc: stable@kernel.org
>> Cc: Daeho Jeong <daehojeong@google.com>
>> Signed-off-by: Chao Yu <chao@kernel.org>
>> ---
>>  fs/f2fs/file.c | 28 +++++++++++++++++-----------
>>  1 file changed, 17 insertions(+), 11 deletions(-)
>>
>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>> index f4facd409d9b..11cc8d79c235 100644
>> --- a/fs/f2fs/file.c
>> +++ b/fs/f2fs/file.c
>> @@ -1107,17 +1107,23 @@ int f2fs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
>>                         !IS_ALIGNED(attr->ia_size,
>>                         F2FS_BLK_TO_BYTES(fi->i_cluster_size)))
>>                         return -EINVAL;
>> -               /*
>> -                * To prevent scattered pin block generation, we don't allow
>> -                * smaller/equal size unaligned truncation for pinned file.
>> -                * We only support overwrite IO to pinned file, so don't
>> -                * care about larger size truncation.
>> -                */
>> -               if (f2fs_is_pinned_file(inode) &&
>> -                       attr->ia_size <= i_size_read(inode) &&
>> -                       !IS_ALIGNED(attr->ia_size,
>> -                       F2FS_BLK_TO_BYTES(CAP_BLKS_PER_SEC(sbi))))
>> -                       return -EINVAL;
>> +
>> +               if (f2fs_is_pinned_file(inode)) {
>> +                       /*
>> +                        * It may break section-aligned fallocate recovery
>> +                        * mechanism, so do not allow larger size truncation.
>> +                        */
>> +                       if (attr->ia_size > i_size_read(inode))
>> +                               return -EINVAL;
> Is it ok if we allow larger size truncation and also  limit it to
> aligned "F2FS_BLK_TO_BYTES(CAP_BLKS_PER_SEC(sbi)"?

No, I think above example will still suffer section-unaligned issue.

Thanks,

> thanks!
>> +                       /*
>> +                        * To prevent scattered pin block generation, we don't
>> +                        * allow smaller/equal size unaligned truncation for
>> +                        * pinned file.
>> +                        */
>> +                       else if (!IS_ALIGNED(attr->ia_size,
>> +                               F2FS_BLK_TO_BYTES(CAP_BLKS_PER_SEC(sbi))))
>> +                               return -EINVAL;
>> +               }
>>         }
>>
>>         if (is_quota_modification(idmap, inode, attr)) {
>> --
>> 2.49.0
>>
>>
>>
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