linux-kernel - Re: [PATCH 1/2] trace_events_filter: use rcu_assign_pointer() when setting ftrace_event

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Date:	Wed, 23 Nov 2011 17:40:17 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] trace_events_filter: use rcu_assign_pointer() when
 setting ftrace_event_call->filter

Le mardi 22 novembre 2011 à 17:46 -0800, Tejun Heo a écrit :
> ftrace_event_call->filter is sched RCU protected but didn't use
> rcu_assign_pointer().  Fix it.
> 
> TODO: Add proper __rcu annotation to call->filter and all its users.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> ---
>  kernel/trace/trace_events_filter.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> Index: work/kernel/trace/trace_events_filter.c
> ===================================================================
> --- work.orig/kernel/trace/trace_events_filter.c
> +++ work/kernel/trace/trace_events_filter.c
> @@ -1686,7 +1686,7 @@ static int replace_system_preds(struct e
>  		 * replace the filter for the call.
>  		 */
>  		filter = call->filter;
> -		call->filter = filter_item->filter;
> +		rcu_assign_pointer(call->filter, filter_item->filter);
>  		filter_item->filter = filter;
>  
>  		fail = false;
> @@ -1741,7 +1741,7 @@ int apply_event_filter(struct ftrace_eve
>  		filter = call->filter;
>  		if (!filter)
>  			goto out_unlock;
> -		call->filter = NULL;
> +		rcu_assign_pointer(call->filter, NULL);

Its a minor point, but setting a pointer to NULL certainly doesnt need a
smp_wmb() barrier, so you can use RCU_INIT_POINTER(call->filter, NULL);



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