Re: [PATCH] fs: fix schedule while atomic caused by gfp of erofs_allocpage

[Gao Xiang <hsiangkao@linux.alibaba.com>]

On 2024/7/16 14:43, Zhaoyang Huang wrote:
> On Tue, Jul 16, 2024 at 2:20 PM Gao Xiang <hsiangkao@linux.alibaba.com> wrote:
>>
>>
>>

...

>>>>
>>>> I don't see why it's an atomic context,
>>>> so this patch is incorrect.
>>> Sorry, I should provide more details. page_cache_ra_unbounded() will
>>> call filemap_invalidate_lock_shared(mapping) to ensure the integrity
>>> of page cache during readahead, which will disable preempt.
>>
>> Why a rwsem sleepable lock disable preemption?
> emm, that's the original design of down_read()

No.

> 
>> context should be always non-atomic context, which is applied
>> to all kernel filesystems.
>   AFAICT, filemap_fault/read have added the folios of readahead to page
> cache which means the aops->readahead basically just need to map the
> block to this folios and then launch the bio. The erofs is a little
> bit different to others as it has to alloc_pages for decompression
> when doing this.

Interesting.  The whole .readahead is sleepable, including
submit block I/Os to storage.

Nacked-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Thanks,
Gao Xiang