linux-kernel - Re: [PATCH v2 3/6] sched/cpufreq: Annotate cpufreq_update_util_data pointer with _

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Message-Id: <20190225211026.GX4072@linux.ibm.com>
Date:   Mon, 25 Feb 2019 13:10:26 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Christian Brauner <christian@...uner.io>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Ahern <dsahern@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Ingo Molnar <mingo@...hat.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Josh Triplett <josh@...htriplett.org>, keescook@...omium.org,
        kernel-hardening@...ts.openwall.com, kernel-team@...roid.com,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        netdev@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        Quentin Perret <quentin.perret@....com>, rcu@...r.kernel.org,
        Song Liu <songliubraving@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        xdp-newbies@...r.kernel.org, Yonghong Song <yhs@...com>
Subject: Re: [PATCH v2 3/6] sched/cpufreq: Annotate cpufreq_update_util_data
 pointer with __rcu

On Sat, Feb 23, 2019 at 01:34:31AM -0500, Joel Fernandes (Google) wrote:
> Recently I added an RCU annotation check to rcu_assign_pointer(). All
> pointers assigned to RCU protected data are to be annotated with __rcu
> inorder to be able to use rcu_assign_pointer() similar to checks in
> other RCU APIs.
> 
> This resulted in a sparse error: kernel//sched/cpufreq.c:41:9: sparse:
> error: incompatible types in comparison expression (different address
> spaces)
> 
> Fix this by annotating cpufreq_update_util_data pointer with __rcu. This
> will also help sparse catch any future RCU misuage bugs.
> 
> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>

>From an RCU perspective:

Reviewed-by: Paul E. McKenney <paulmck@...ux.ibm.com>

> ---
>  kernel/sched/cpufreq.c | 2 +-
>  kernel/sched/sched.h   | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/cpufreq.c b/kernel/sched/cpufreq.c
> index 22bd8980f32f..e316ee7bb2e5 100644
> --- a/kernel/sched/cpufreq.c
> +++ b/kernel/sched/cpufreq.c
> @@ -7,7 +7,7 @@
>   */
>  #include "sched.h"
>  
> -DEFINE_PER_CPU(struct update_util_data *, cpufreq_update_util_data);
> +DEFINE_PER_CPU(struct update_util_data __rcu *, cpufreq_update_util_data);
>  
>  /**
>   * cpufreq_add_update_util_hook - Populate the CPU's update_util_data pointer.
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index d04530bf251f..2ab545d40381 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2166,7 +2166,7 @@ static inline u64 irq_time_read(int cpu)
>  #endif /* CONFIG_IRQ_TIME_ACCOUNTING */
>  
>  #ifdef CONFIG_CPU_FREQ
> -DECLARE_PER_CPU(struct update_util_data *, cpufreq_update_util_data);
> +DECLARE_PER_CPU(struct update_util_data __rcu *, cpufreq_update_util_data);
>  
>  /**
>   * cpufreq_update_util - Take a note about CPU utilization changes.
> -- 
> 2.21.0.rc0.258.g878e2cd30e-goog
>