[PATCH 1/5] tracing: Fix initialization failure path in tracing_set_tracer()

[Steven Rostedt]

On Sat, 2012-05-26 at 06:39 -0700, Anton Vorontsov wrote:
> If tracer->init() fails, current code will leave current_tracer pointing
> to an unusable tracer, which at best makes 'current_tracer' report
> inaccurate value.
> 
> Fix the issue by pointing current_tracer to nop tracer, and only update
> current_tracer with the new one after all the initialization succeeds.
> 

Hmm, I'll look at this in more detail. This may be something I pull now.
(for 3.6).

-- Steve

> Signed-off-by: Anton Vorontsov <anton.vorontsov at linaro.org>
> ---
>  kernel/trace/trace.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 68032c6..5cf7e67 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3172,10 +3172,10 @@ static int tracing_set_tracer(const char *buf)
>  	}
>  	destroy_trace_option_files(topts);
>  
> -	current_trace = t;
> +	current_trace = &nop_trace;
>  
> -	topts = create_trace_option_files(current_trace);
> -	if (current_trace->use_max_tr) {
> +	topts = create_trace_option_files(t);
> +	if (t->use_max_tr) {
>  		int cpu;
>  		/* we need to make per cpu buffer sizes equivalent */
>  		for_each_tracing_cpu(cpu) {
> @@ -3195,6 +3195,7 @@ static int tracing_set_tracer(const char *buf)
>  			goto out;
>  	}
>  
> +	current_trace = t;
>  	trace_branch_enable(tr);
>   out:
>  	mutex_unlock(&trace_types_lock);