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References: <20200324153643.15527-1-will@kernel.org> <20200324153643.15527-4-will@kernel.org>
 <20200324165128.GS20696@hirez.programming.kicks-ass.net>
In-Reply-To: <20200324165128.GS20696@hirez.programming.kicks-ass.net>
From:   Jann Horn <jannh@google.com>
Date:   Tue, 24 Mar 2020 17:56:15 +0100
Message-ID: <CAG48ez2WJo5+wqWi1nxstR=WWyseVfZPMnpdDBsZKW5G+Tt3KQ@mail.gmail.com>
Subject: Re: [RFC PATCH 03/21] list: Annotate lockless list primitives with data_race()
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Will Deacon <will@kernel.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        Kees Cook <keescook@chromium.org>,
        Maddie Stone <maddiestone@google.com>,
        Marco Elver <elver@google.com>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        kernel-team <kernel-team@android.com>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        Oleg Nesterov <oleg@redhat.com>
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On Tue, Mar 24, 2020 at 5:51 PM Peter Zijlstra <peterz@infradead.org> wrote:
> On Tue, Mar 24, 2020 at 03:36:25PM +0000, Will Deacon wrote:
> > diff --git a/include/linux/list.h b/include/linux/list.h
> > index 4fed5a0f9b77..4d9f5f9ed1a8 100644
> > --- a/include/linux/list.h
> > +++ b/include/linux/list.h
> > @@ -279,7 +279,7 @@ static inline int list_is_last(const struct list_head *list,
> >   */
> >  static inline int list_empty(const struct list_head *head)
> >  {
> > -     return READ_ONCE(head->next) == head;
> > +     return data_race(READ_ONCE(head->next) == head);
> >  }
>
> list_empty() isn't lockless safe, that's what we have
> list_empty_careful() for.

That thing looks like it could also use some READ_ONCE() sprinkled in...