linux-kernel - Re: [PATCH v6] Unified trace buffer

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Date:	Fri, 26 Sep 2008 22:08:50 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	prasad@...ux.vnet.ibm.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	"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 v6] Unified trace buffer

On Fri, 2008-09-26 at 14:05 -0400, Steven Rostedt wrote:
> +static void
> +rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned
> nr_pages)
> +{
> +       struct page *page;
> +       struct list_head *p;
> +       unsigned i;
> +
> +       atomic_inc(&cpu_buffer->record_disabled);

You probably want synchronize_sched() here (and similar other places) to
ensure any active writer on the corresponding cpu is actually stopped.

Which suggests you want to use something like ring_buffer_lock_cpu() and
implement that as above.

> +       for (i = 0; i < nr_pages; i++) {
> +               BUG_ON(list_empty(&cpu_buffer->pages));
> +               p = cpu_buffer->pages.next;
> +               page = list_entry(p, struct page, lru);
> +               list_del_init(&page->lru);
> +               __free_page(page);
> +       }
> +       BUG_ON(list_empty(&cpu_buffer->pages));
> +
> +       __ring_buffer_reset_cpu(cpu_buffer);
> +
> +       check_pages(cpu_buffer);
> +
> +       atomic_dec(&cpu_buffer->record_disabled);
> +
> +}

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