Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230722074753.568696-1-arnd@kernel.org> <CALOAHbCV2v3X7g1TD42yve0juhRD2vhq=DMtDz9P6+mX8Dae_w@mail.gmail.com>
 <CAADnVQKGe8DN+Zs387UVwpij3ROGqNEnc5r940h5ueqQYHTYCA@mail.gmail.com>
 <fa5e9098-d6f9-48a2-bb77-2620b6bb6556@app.fastmail.com> <CAADnVQ+p4wpd=tKJAiwB34O1y5vv4mibtkt9D-F7sG=rQapcew@mail.gmail.com>
 <679d8d63-ce92-4294-8620-e98c82365b2c@app.fastmail.com> <39444a4e-70da-4d17-a40a-b51e05236d23@app.fastmail.com>
 <CAADnVQ+zdV9+UNV9NeEzY2rWd8qvW3cvHxS9mYwfhnqZOV+9=A@mail.gmail.com> <3e202277-fe74-4105-93ec-b646efaaa956@app.fastmail.com>
In-Reply-To: <3e202277-fe74-4105-93ec-b646efaaa956@app.fastmail.com>
From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Tue, 25 Jul 2023 11:15:53 -0700
Message-ID: <CAADnVQJWfQVGWsruzTHB9v=kztkDeRbJJDANafVScEE4EJ1jbg@mail.gmail.com>
Subject: Re: [PATCH] bpf: force inc_active()/dec_active() to be inline functions
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Arnd Bergmann <arnd@kernel.org>,
        Yafang Shao <laoar.shao@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Hou Tao <houtao1@huawei.com>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Kumar Kartikeya Dwivedi <memxor@gmail.com>,
        bpf <bpf@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Mon, Jul 24, 2023 at 1:41=E2=80=AFPM Arnd Bergmann <arnd@arndb.de> wrote=
:
>
> On Mon, Jul 24, 2023, at 21:15, Alexei Starovoitov wrote:
> > On Mon, Jul 24, 2023 at 11:30=E2=80=AFAM Arnd Bergmann <arnd@kernel.org=
> wrote:
> >> On Mon, Jul 24, 2023, at 20:13, Arnd Bergmann wrote:
> >>
> >> I have a minimized test case at https://godbolt.org/z/hK4ev17fv
> >> that shows the problem happening with all versions of gcc
> >> (4.1 through 14.0) if I force the dec_active() function to be
> >> inline and force inc_active() to be non-inline.
> >
> > That's a bit of cheating, but I see your point now.
> > How about we do:
> > diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
> > index 51d6389e5152..3fa0944cb975 100644
> > --- a/kernel/bpf/memalloc.c
> > +++ b/kernel/bpf/memalloc.c
> > @@ -183,11 +183,11 @@ static void inc_active(struct bpf_mem_cache *c,
> > unsigned long *flags)
> >         WARN_ON_ONCE(local_inc_return(&c->active) !=3D 1);
> >  }
> >
> > -static void dec_active(struct bpf_mem_cache *c, unsigned long flags)
> > +static void dec_active(struct bpf_mem_cache *c, unsigned long *flags)
> >  {
> >         local_dec(&c->active);
> >         if (IS_ENABLED(CONFIG_PREEMPT_RT))
> > -               local_irq_restore(flags);
> > +               local_irq_restore(*flags);
> >  }
>
>
> Sure, that's fine. Between this and the two suggestions I had
> (__always_inline or passing the flags from  inc_active as a
> return code), I don't have a strong preference, so pick whichever
> you like.

I think:
static void dec_active(struct bpf_mem_cache *c, unsigned long *flags)
is cleaner.
Could you send a patch?