Re: [GIT PULL] hotfixes for 6.2

[Baolin Wang]

On 2/14/2023 6:19 AM, Linus Torvalds wrote:
> On Mon, Feb 13, 2023 at 2:08 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > Kuan-Ying Lee (1):
> >        mm/gup: add folio to list when folio_isolate_lru() succeed
>
> Ugh. I really hate fixes like this.
>
> The problem came from mis-understanding the return value of
> folio_isolate_lru(), and thinking that it was a boolean
> success/failure thing.
>
> It wasn't, it was an integer "success/errno" thing, and the sense of
> the test was wrong. So the patch is
>
> -       if (!folio_isolate_lru(folio))
> +       if (folio_isolate_lru(folio))
>                  continue;
>
> but at no point was the code *clarified*.
>
> Wouldn't it have been much better to write the new code to be
>
>          if (folio_isolate_lru(folio) < 0)
>                  continue;
>
> to actually make it clear that this is a "negative error return check".
>
> I've pulled this, but I really think that when somebody notices that
> we had a silly bug because of a misunderstanding like this, it's not
> just that the bug should be fixed, the code should also be *clarified*
> at the same time.

Yes, agree, I need to check the return value of folio_isolate_lru() 
every time when looking at the code. I can help to create a patch to 
make it clear for all users.