linux-kernel - Re: [PATCH -mm v2] mm/page_isolation: fix potential warning from user

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Date:   Mon, 20 Jan 2020 16:43:15 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Qian Cai <cai@....pw>, Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm v2] mm/page_isolation: fix potential warning from user

On Mon 20-01-20 15:13:54, David Hildenbrand wrote:
> On 20.01.20 15:11, Qian Cai wrote:
> >> On Jan 20, 2020, at 9:01 AM, David Hildenbrand <david@...hat.com> wrote:
> >> On 20.01.20 14:56, Qian Cai wrote:
[...]
> >>>> FWIW, I'd prefer this change without any such cleanups (e.g., I don't
> >>>> like returning a bool from this function and the IS_ERR handling, makes
> >>>> the function harder to read than before)
> >>>
> >>> What is Michal or Andrew’s opinion? BTW, a bonus point to return a bool
> >>> is that it helps the code robustness in general, as UBSAN will be able to
> >>> catch any abuse.
> >>>
> >>
> >> A return type of bool on a function that does not test a property
> >> ("has_...", "is"...") is IMHO confusing.
> > 
> > That is fine. It could be renamed to set_migratetype_is_isolate() or
> > is_set_migratetype_isolate() which seems pretty minor because we
> > have no consistency in the naming of this in linux kernel at all, i.e.,
> > many existing bool function names without those test of properties. 
> 
> It does not query a property, so "is_set_migratetype_isolate()" is plain
> wrong.
> 
> Anyhow, Michal does not seem to care.

Well, TBH I have missed this change. My bad. I have mostly checked that
the WARN_ONCE is not gated by the check and didn't expect more changes.
But I have likely missed that change in the previous version already.
You guys are too quick with new version to my standard.

Anyway, I do agree that bool is clumsy here. Returning false on success
is just head scratching. Nobody really consumes the errno value but I
would just leave it that way or if there is a strong need to change then
do it in a separate patch.
-- 
Michal Hocko
SUSE Labs