linux-kernel - Re: Question about the barrier() in hlist_nulls_for_each_entry

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Message-ID: <CANn89iKJWw7zUP-E_d=Yhaz=Qw0R3Ae7ULaGgrtsi1yf2pfpGg@mail.gmail.com>
Date:   Thu, 20 Jul 2023 21:22:27 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Alan Huang <mmpgouride@...il.com>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        rcu@...r.kernel.org, "Paul E. McKenney" <paulmck@...nel.org>,
        roman.gushchin@...ux.dev
Subject: Re: Question about the barrier() in hlist_nulls_for_each_entry_rcu()

On Thu, Jul 20, 2023 at 8:54 PM Alan Huang <mmpgouride@...il.com> wrote:
>
> Hi,
>
> I noticed a commit c87a124a5d5e(“net: force a reload of first item in hlist_nulls_for_each_entry_rcu”)
> and a related discussion [1].
>
> After reading the whole discussion, it seems like that ptr->field was cached 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-glaptop/
>
> Thanks,
> Alan