linux-kernel - Re: [PATCH] tracing: Check result of ring_buffer_read

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Date:	Fri, 12 Apr 2013 23:00:30 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Namhyung Kim <namhyung.kim@....com>
Subject: Re: [PATCH] tracing: Check result of ring_buffer_read_prepare()

On Wed, 2013-04-10 at 10:55 +0900, Namhyung Kim wrote:
> From: Namhyung Kim <namhyung.kim@....com>
> 
> 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@...dmis.org>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  kernel/trace/trace.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 7270460cfe3c..13200de31f0b 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;
>  		}

OK, this totally fails. I guess we need to allow
ring_buffer_read_prepare() to return NULL, as it will return NULL if a
cpu is offline or the tracing_cpumask has a CPU down.

I'll just pull this patch out of my queue for now.

-- Steve

>  		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 +2852,23 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot)
>  
>  	return iter;
>  
> +free:
> +	/*
> +	 * For simplicity, just keep single loop without comparing cpu_file.
> +	 */
> +	for_each_tracing_cpu(cpu) {
> +		if (iter->buffer_iter[cpu])
> +			ring_buffer_read_finish(iter->buffer_iter[cpu]);
> +	}
> +
> +	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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