linux-kernel - Re: [PATCH 1/2] mm/mempolicy: Allow lookup

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Date:   Thu, 9 Apr 2020 09:42:20 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Peter Xu <peterx@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        syzbot+693dc11fcb53120b5559@...kaller.appspotmail.com
Subject: Re: [PATCH 1/2] mm/mempolicy: Allow lookup_node() to handle fatal signal

On Thu, Apr 9, 2020 at 12:03 AM Michal Hocko <mhocko@...nel.org> wrote:
>
> This patch however doesn't go all the way to revert it because 0 return
> value is impossible.

I'm not convinced it's impossible. And if it is, then the current code
is harmless.

Now, I do agree that we probably should go through and clarify the
whole range of different get_user_pages() cases of returning zero (or
not doing so), but right now it's so confusing that I'd prefer to keep
that (possibly unnecessary) belt-and-suspenders check for zero in
there.

If/when somebody actually does a real audit and the result is "these
functions cannot return zero" and it's documented, then we can remove
those checks.

Ok?

              Linus