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: <04C1E631-725C-47AD-9914-25D5CE04DFF4@gmail.com>
In-Reply-To: <04C1E631-725C-47AD-9914-25D5CE04DFF4@gmail.com>
From:   Eric Dumazet <edumazet@google.com>
Date:   Thu, 20 Jul 2023 21:22:27 +0200
Message-ID: <CANn89iKJWw7zUP-E_d=Yhaz=Qw0R3Ae7ULaGgrtsi1yf2pfpGg@mail.gmail.com>
Subject: Re: Question about the barrier() in hlist_nulls_for_each_entry_rcu()
To:     Alan Huang <mmpgouride@gmail.com>
Cc:     linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        rcu@vger.kernel.org, "Paul E. McKenney" <paulmck@kernel.org>,
        roman.gushchin@linux.dev
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Thu, Jul 20, 2023 at 8:54=E2=80=AFPM Alan Huang <mmpgouride@gmail.com> w=
rote:
>
> Hi,
>
> I noticed a commit c87a124a5d5e(=E2=80=9Cnet: force a reload of first ite=
m in hlist_nulls_for_each_entry_rcu=E2=80=9D)
> and a related discussion [1].
>
> After reading the whole discussion, it seems like that ptr->field was cac=
hed by gcc even with the deprecated
> ACCESS_ONCE(), so my question is:
>
>         Is that a compiler bug? If so, has this bug been fixed today, ten=
 years later?
>
>         What about READ_ONCE(ptr->field)?

Make sure sparse is happy.

Do you have a patch for review ?


>
>
> [1] https://lore.kernel.org/all/1369699930.3301.494.camel@edumazet-glapto=
p/
>
> Thanks,
> Alan