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From:   Axel Rasmussen <axelrasmussen@google.com>
Date:   Fri, 7 Jul 2023 13:38:16 -0700
Message-ID: <CAJHvVci6qCv+d7Hz0QkqeuEZze0OFJt0P9qnWgA_cgDeaLmptQ@mail.gmail.com>
Subject: Re: [PATCH v3 7/8] selftests/mm: refactor uffd_poll_thread to allow
 custom fault handlers
To:     Peter Xu <peterx@redhat.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Brian Geffon <bgeffon@google.com>,
        Christian Brauner <brauner@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Gaosheng Cui <cuigaosheng1@huawei.com>,
        Huang Ying <ying.huang@intel.com>,
        Hugh Dickins <hughd@google.com>,
        James Houghton <jthoughton@google.com>,
        "Jan Alexander Steffens (heftig)" <heftig@archlinux.org>,
        Jiaqi Yan <jiaqiyan@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        "Liam R. Howlett" <Liam.Howlett@oracle.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        "Mike Rapoport (IBM)" <rppt@kernel.org>,
        Muchun Song <muchun.song@linux.dev>,
        Nadav Amit <namit@vmware.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        Ryan Roberts <ryan.roberts@arm.com>,
        Shuah Khan <shuah@kernel.org>,
        Suleiman Souhlal <suleiman@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        "T.J. Alumbaugh" <talumbau@google.com>,
        Yu Zhao <yuzhao@google.com>,
        ZhangPeng <zhangpeng362@huawei.com>, linux-doc@vger.kernel.org,
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On Fri, Jul 7, 2023 at 10:03=E2=80=AFAM Axel Rasmussen <axelrasmussen@googl=
e.com> wrote:
>
> On Fri, Jul 7, 2023 at 6:42=E2=80=AFAM Peter Xu <peterx@redhat.com> wrote=
:
> >
> > On Thu, Jul 06, 2023 at 03:50:35PM -0700, Axel Rasmussen wrote:
> > > @@ -247,9 +245,13 @@ static int userfaultfd_stress(void)
> > >  {
> > >       void *area;
> > >       unsigned long nr;
> > > -     struct uffd_args args[nr_cpus];
> > > +     struct uffd_args *args;
> > >       uint64_t mem_size =3D nr_pages * page_size;
> > >
> > > +     args =3D calloc(nr_cpus, sizeof(struct uffd_args));
> > > +     if (!args)
> > > +             err("allocating args array failed");
> >
> > This is trivial, but I think I requested a "free" (or keep it allocate =
on
> > stack) in previous version but it didn't get a response on why we canno=
t
> > and it kept going..  could you help explain?
>
> Oh, sorry! I had meant to change this after our discussion, and simply
> overlooked it while reworking the patches.
>
> I'll include this change in a v4 which also addresses e.g. the
> comments on commit 1.

Ah, so I tried switching back to the {0} initializer, and was reminded
why I didn't do that in v1. :) Ignoring the missing braces warning I
talked about before, using {0} here is actually an error
("variable-sized object may not be initialized") because this is a
variable sized array (nr_cpus isn't constant). So, that option is out.

I'm not a huge fan of adding the free() cleanup and dealing with all
of the err() calls this function has.

Originally I switched to calloc() because I'm not a big fan of VLAs
anyway. But, as a compromise in v4 I'll leave it a VLA, and switch to
memset() for initializing it.

>
> >
> > --
> > Peter Xu
> >