Re: [PATCH v2 2/3] mm/swapfile: fix possible data races of inuse_pages

[Miaohe Lin]

On 2022/6/21 11:39, Muchun Song wrote:
> On Tue, Jun 21, 2022 at 09:14:00AM +0800, Huang, Ying wrote:
>> Qian Cai <quic_qiancai@xxxxxxxxxxx> writes:
>>
>>> On Mon, Jun 20, 2022 at 10:20:07PM +0800, Muchun Song wrote:
>>>> The lock does not protect the read sides. So the write side should be
>>>> fixed by WRITTE_ONCE().
>>>
>>> https://lwn.net/Articles/816854/
>>>
>>> "Unmarked writes (aligned and up to word size) can be treated as if they had
>>> used WRITE_ONCE() by building with
>>> CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=y (also selected by default).
> 
> All right, CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC help us avoid KCSAN
> complaining.
> 
>>> Experience has shown that compilers are much less likely to destructively
>>> optimize in-kernel writes than reads. Some developers might therefore
>>> choose to use READ_ONCE() but omit the corresponding WRITE_ONCE(). Other
>>> developers might prefer the documentation benefits and long-term peace of
>>> mind accruing from explicit use of WRITE_ONCE()..."
>>
>> Thanks for pointing me to this great article.  So although not required
>> by KCSAN strictly, WRITE_ONCE() is still good for documentation, etc.
>> Just like we have done for swap_info_struct->highest_bit, etc.
>>
> 
> +1

I tend to agree with Muchun & Huang, Ying. Thanks all of you.

> 
>> Best Regards,
>> Huang, Ying
>>
> .
>