Re: [PATCH 3/3] tracing: Check cpu file on tracing_release()

[Steven Rostedt]

On Wed, 2013-04-10 at 10:30 +0900, Namhyung Kim wrote:

> >From 7ba245dba217ef858b467552019acd49f7fdce7e Mon Sep 17 00:00:00 2001
> From: Namhyung Kim <namhyung.kim@xxxxxxx>
> Date: Wed, 10 Apr 2013 09:10:44 +0900
> Subject: [PATCH] tracing: Check result of ring_buffer_read_prepare()
> 
> The ring_buffer_read_prepare() can return NULL if memory allocation
> fails.  Fail out in this case instead of succedding and then having
> no output.
> 
> Suggested-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
> ---
>  kernel/trace/trace.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 7270460cfe3c..3b3514dc8e5e 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2826,6 +2826,8 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot)
>  		for_each_tracing_cpu(cpu) {
>  			iter->buffer_iter[cpu] =
>  				ring_buffer_read_prepare(iter->trace_buffer->buffer, cpu);
> +			if (!iter->buffer_iter[cpu])
> +				goto free;
>  		}
>  		ring_buffer_read_prepare_sync();
>  		for_each_tracing_cpu(cpu) {
> @@ -2836,6 +2838,9 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot)
>  		cpu = iter->cpu_file;
>  		iter->buffer_iter[cpu] =
>  			ring_buffer_read_prepare(iter->trace_buffer->buffer, cpu);
> +		if (!iter->buffer_iter[cpu])
> +			goto free;
> +
>  		ring_buffer_read_prepare_sync();
>  		ring_buffer_read_start(iter->buffer_iter[cpu]);
>  		tracing_iter_reset(iter, cpu);
> @@ -2847,6 +2852,26 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot)
>  
>  	return iter;
>  
> +free:
> +	if (iter->cpu_file == RING_BUFFER_ALL_CPUS) {
> +		for_each_tracing_cpu(cpu) {
> +			if (iter->buffer_iter[cpu])
> +				ring_buffer_read_finish(iter->buffer_iter[cpu]);
> +		}
> +	} else {
> +		cpu = iter->cpu_file;
> +		if (iter->buffer_iter[cpu])
> +			ring_buffer_read_finish(iter->buffer_iter[cpu]);
> +	}

As I said I would consider updating the release code, but here, it's an
error path that is extremely unlikely to be hit. Please just keep the
single loop, and leave out the cpu_file compare.

Thanks,

-- Steve

> +
> +	if (iter->trace && iter->trace->close)
> +		iter->trace->close(iter);
> +
> +	if (!iter->snapshot)
> +		tracing_start_tr(tr);
> +
> +	mutex_destroy(&iter->mutex);
> +	free_cpumask_var(iter->started);
>   fail:
>  	mutex_unlock(&trace_types_lock);
>  	kfree(iter->trace);


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