linux-kernel - Re: [PATCH] ring_buffer: map to cpu not page

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Date:	Fri, 3 Oct 2008 09:27:22 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Jonathan Corbet <corbet@....net>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	prasad@...ux.vnet.ibm.com, "Frank Ch. Eigler" <fche@...hat.com>,
	David Wilder <dwilder@...ibm.com>, hch@....de,
	Martin Bligh <mbligh@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH] ring_buffer: map to cpu not page


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

> My original patch had a compile bug when NUMA was configured. I 
> referenced cpu when it should have been cpu_buffer->cpu.
> 
> Ingo quickly fixed this bug by replacing cpu with 'i' because that was 
> the loop counter. Unfortunately, the 'i' was the counter of pages, not 
> CPUs. This caused a crash when the number of pages allocated for the 
> buffers exceeded the number of pages, which would usually be the case.
> 
> Signed-off-by: Steven Rostedt <srostedt@...hat.com>

>  	for (i = 0; i < nr_pages; i++) {
>  		page = kzalloc_node(ALIGN(sizeof(*page), cache_line_size()),
> -				    GFP_KERNEL, cpu_to_node(i));
> +				    GFP_KERNEL, cpu_to_node(cpu_buffer->cpu));

oh, stupid typo of the year :-)

applied to tip/tracing/ring-buffer, thanks for tracking it down! I've 
reactivated the topic branch for tip/master and i'm running a few tests 
before pushing it out for wider testing.

	Ingo
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