Re: [PATCH 1/2] mm/MADV_COLLAPSE: set EAGAIN on unexpected page refcount

Andrew Morton
2023-02-09T22:12:29Z

On Thu, 9 Feb 2023 13:50:30 -0800 (PST) Hugh Dickins <hughd@google.com> wrote:

>
> >
> > I'm not seeing anything in the [1/2] changelog which indicates that a
> > backport is needed. IOW,
>
> Correct: it's just changing the errno for some racy cases from "you're
> wrong, don't bother me again" to "it might be worth having another go":
> not fixing an instability, as 2/2 was.
>
> >
> > # cat .signature
> > When fixing a bug, please describe the end-user visible effects of that bug.
>
> If whatever's being run by the end-user is coded to try again on -EAGAIN,
> then the end-user will less often see occasional unexplained failures.
>

OK, thanks. I redid the changelog's final paragraph thusly:

: In this situation, MADV_COLLAPSE returns -EINVAL when it should return
: -EAGAIN. This could cause userspace to conclude that the syscall failed,
: when it in fact could succeed by retrying.