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

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

On 2024/7/16 14:46, Gao Xiang wrote:
> 
> 
> 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.

Also, please don't imagine your stack trace if it's a non-upstream
kernel.

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