linux-kernel - Re: [RFC PATCH 03/21] list: Annotate lockless list primitives with data

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Message-ID: <20200324165128.GS20696@hirez.programming.kicks-ass.net>
Date:   Tue, 24 Mar 2020 17:51:28 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Will Deacon <will@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Maddie Stone <maddiestone@...gle.com>,
        Marco Elver <elver@...gle.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, kernel-team@...roid.com,
        kernel-hardening@...ts.openwall.com,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [RFC PATCH 03/21] list: Annotate lockless list primitives with
 data_race()

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.