Re: [PATCH] events: Protect access via task_subsys_state_check()

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Fri, 2013-04-19 at 12:01 -0700, Paul E. McKenney wrote:
> The following RCU splat indicates lack of RCU protection:

...

> This commit therefore adds the required RCU read-side critical section to
> perf_event_comm().
> 
> Reported-by: Adam Jackson <ajax@redhat.com>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Tested-by: Gustavo Luiz Duarte <gusld@br.ibm.com>

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index b0cd865..8db9551 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4593,6 +4593,7 @@ void perf_event_comm(struct task_struct *task)
>  	struct perf_event_context *ctx;
>  	int ctxn;
>  
> +	rcu_read_lock();
>  	for_each_task_context_nr(ctxn) {
>  		ctx = task->perf_event_ctxp[ctxn];
>  		if (!ctx)
> @@ -4600,6 +4601,7 @@ void perf_event_comm(struct task_struct *task)
>  
>  		perf_event_enable_on_exec(ctx);
>  	}
> +	rcu_read_unlock();
>  
>  	if (!atomic_read(&nr_comm_events))
>  		return;
>