linux-kernel - Re: [PATCH v3] trace: Add per_cpu ring buffer control files

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Date:	Mon, 22 Aug 2011 20:49:00 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Vaibhav Nagarnaik <vnagarnaik@...gle.com>
Cc:	Michael Rubin <mrubin@...gle.com>,
	David Sharp <dhsharp@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] trace: Add per_cpu ring buffer control files

On Mon, 2011-08-22 at 15:09 -0700, Vaibhav Nagarnaik wrote:
>  
> @@ -3740,10 +3757,6 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
>  	    !cpumask_test_cpu(cpu, buffer_b->cpumask))
>  		goto out;
>  
> -	/* At least make sure the two buffers are somewhat the same */
> -	if (buffer_a->pages != buffer_b->pages)
> -		goto out;
> -
>  	ret = -EAGAIN;
>  
>  	if (ring_buffer_flags != RB_BUFFERS_ON)
> @@ -3758,6 +3771,12 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
>  	cpu_buffer_a = buffer_a->buffers[cpu];
>  	cpu_buffer_b = buffer_b->buffers[cpu];

I would move the cpu_buffer_(ab) assignments up instead, as I want the
EINVAL to have dominance. The record_disable just says that we are
temporarily out of commission, when in fact it could be invalid. Thus
the invalid conditions need to be treated first.

-- Steve

>  
> +	ret = -EINVAL;
> +	/* At least make sure the two buffers are somewhat the same */
> +	if (cpu_buffer_a->pages != cpu_buffer_b->pages)
> +		goto out;
> +
> +	ret = -EAGAIN;
>  	if (atomic_read(&cpu_buffer_a->record_disabled))
>  		goto out;
>  


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