Re: [PATCH v2] mm/mmap.c: use IS_ERR_VALUE to check return value of get_unmapped_area

[gaowei Pu <pugaowei@gmail.com>]

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On Tue, Oct 15, 2019 at 8:33 PM Michal Hocko <mhocko@suse.com> wrote:

> On Sat 12-10-19 18:25:12, Gaowei Pu wrote:
> > get_unmapped_area already cover the offset_in_page() check and returned
> > with error ptr. So replace offset_in_page() with IS_ERR_VALUE().
>
> I have to say that I found offset_in_page check quite unintuitive. It is
> a relict from the past I suspect. A newer code seems to use
> IS_ERR_VALUE. If we want to make the code consistent then I am for it.
> Could you check other users as well? git grep suggests checking
> kernel/events/uprobes.c, mm/mmap.c and mm/mremap.c.
>
I only noticed the offset_in_page check after returned from get_unmapped_area
is redundant.
So I just replace the places where get_unmapped_area returned. As you
mentioned, IS_ERR_VALUE maybe
the newer code to check the error ptr compared to offset_in_page which is
really unintuitive and therefore I will
replace them in mm/mmap.c and mm/mremap.c.

> I would simply use the following for the changelog
> "
> get_unmapped_area returns an address or -errno on failure. Historically
> we have checked for the failure by offset_in_page() which is correct but
> quite hard to read. Newer code started using IS_ERR_VALUE which is much
> easier to read. Convert remaining users of offset_in_page as well.
>
> This shouldn't introduce any functional changes.
> "
>
> OK, I will use your changelog and resend a patch. Thanks.

>
> > 2.23.0
> >
>
> --
> Michal Hocko
> SUSE Labs
>

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