linux-kernel - Re: [PATCH 2/2] events: callchain: Use RCU API to access RCU pointer

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Date:   Wed, 29 Jan 2020 17:19:09 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Amol Grover <frextrite@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        Madhuparna Bhowmik <madhuparnabhowmik04@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH 2/2] events: callchain: Use RCU API to access RCU pointer

On Wed, Jan 29, 2020 at 09:38:13PM +0530, Amol Grover wrote:
> callchain_cpus_entries is annotated as an RCU pointer.
> Hence rcu_dereference_protected or similar RCU API is
> required to dereference the pointer.
> 
> This fixes the following sparse warning
> kernel/events/callchain.c:65:17: warning: incorrect type in assignment
> 
> Signed-off-by: Amol Grover <frextrite@...il.com>
> ---
>  kernel/events/callchain.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
> index f91e1f41d25d..a672d02a1b3a 100644
> --- a/kernel/events/callchain.c
> +++ b/kernel/events/callchain.c
> @@ -62,7 +62,8 @@ static void release_callchain_buffers(void)
>  {
>  	struct callchain_cpus_entries *entries;
>  
> -	entries = callchain_cpus_entries;
> +	entries = rcu_dereference_protected(callchain_cpus_entries,
> +					    lockdep_is_held(&callchain_mutex));


Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>

thanks,

 - Joel


>  	RCU_INIT_POINTER(callchain_cpus_entries, NULL);
>  	call_rcu(&entries->rcu_head, release_callchain_buffers_rcu);
>  }
> -- 
> 2.24.1
>