linux-kernel - Re: [PATCH v2 1/1] ftrace: do not update max buffer with no users

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Date:	Thu, 13 Nov 2008 14:19:39 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Pekka Paalanen <pq@....fi>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH v2 1/1] ftrace: do not update max buffer with no users


* Steven Rostedt <rostedt@...dmis.org> wrote:

> The line count is very misleading. The 83 insertions and deletions where 
> moved code or indentation:

but that indentation is completely unnecessary:

> -               ret = ring_buffer_resize(max_tr.buffer, val);
> -               if (ret < 0) {
> -                       int r;
> -                       cnt = ret;
> -                       r = ring_buffer_resize(global_trace.buffer,
> -                                              global_trace.entries);
> -                       if (r < 0) {
> -                               /* AARGH! We are left with different
> -                                * size max buffer!!!! */
> -                               WARN_ON(1);
> -                               tracing_disabled = 1;
>                         }
> -                       goto out;
>                 }
> 
> 
> +               if (max_tr.buffer) {
> +                       ret = ring_buffer_resize(max_tr.buffer, val);
> +                       if (ret < 0) {
> +                               int r;
> +                               cnt = ret;
> +                               r = ring_buffer_resize(global_trace.buffer,
> +                                                      global_trace.entries);
> +                               if (r < 0) {
> +                                       /* AARGH! We are left with different
> +                                        * size max buffer!!!! */
> +                                       WARN_ON(1);
> +                                       tracing_disabled = 1;
> +                               }
> +                               goto out;
>                         }
>                 }

the obvious solution is to add this to ring_buffer_resize():

	if (!buffer)
		return size;

resizing a non-existent buffer should succeed. A two-liner patch. Not 
160 lines of flux.

Really, you need to think _hard_ how to avoid invasive-looking changes 
in late -rc's, because every extra line to review uses up precious 
review resources.

	Ingo
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