Re: [f2fs-dev] [PATCH] f2fs: fix to prevent clearing immutable for large folio supported inode

[Chao Yu <chao@kernel.org>]

On 1/22/2026 10:02 AM, Nanzhe Zhao wrote:
> Hi all:
> 
> 在 2026/1/9 16:44, Chao Yu via Linux-f2fs-devel 写道:
> 
>> w/ above locks, it seems there is still a race condition as below:
>>
>> f2fs_fileattr_set                read
>>    - f2fs_setflags_common
>>     - truncate_pagecache
>>                           - f2fs_read_data_large_folio
>>                           : read large folios
>>     - mapping_set_folio_order_range
>>
>> Thanks,
> 
> I noticed that the comment for `mapping_set_folio_order_range()` says:
> 
>> "Context: This should not be called while the inode is active as it is non-atomic."
> 
> I'm not sure whether cases like f2fs_fileattr_set falls into the inode
> active case.
> 
>>>
>>>
>>> If clearing immutable is indeed rare, we may leave this as is, since
>>> writes are not supported until the page cache is fully dropped.
>>> Eventually, we will support large folios on non-immutable files.
>>>
>>> Thanks
>>> Barry
> 
> Also, I couldn’t find any API in `include/linux/pagemap.h` that can
> atomically set the
> folio order range. However, I think dynamically setting large folio
> order while an inode
> is active is a reasonable requirement. In my non immutable file large
> folio write work, I need to enable large folio support for a file when
> it is converted from an inline file to a non-inline file. The lack of an
> atomic API seems to be a blocker for moving large folio write forward.
> Any idea on that?

IIUC, our concern here is to avoid "echo 3 > drop_caches", right?

If so, can we try this in new ioctl?
- kern_path(target_file_path)
- d_invalidate(path->dentry)
- path_put

> 
> Thanks,
> Nanzhe Zhao
> 
>