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Subject: Re: [PATCH v6] Unified trace buffer
From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
       Thomas Gleixner <tglx@linutronix.de>,
       Andrew Morton <akpm@linux-foundation.org>, prasad@linux.vnet.ibm.com,
       Linus Torvalds <torvalds@linux-foundation.org>,
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       Christoph Hellwig <hch@infradead.org>,
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       Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
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Date: Fri, 26 Sep 2008 22:08:50 +0200
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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);
> +
> +}