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Subject: Re: [PATCH 1/7] perf_counter: fix dynamic irq_period logging
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>, Corey Ashford <cjashfor@linux.vnet.ibm.com>,
       linux-kernel@vger.kernel.org,
       Arnaldo Carvalho de Melo <acme@redhat.com>,
       John Kacur <jkacur@redhat.com>
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Date: Mon, 25 May 2009 09:19:52 +0200
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On Mon, 2009-05-25 at 10:08 +1000, Paul Mackerras wrote:
> Peter Zijlstra writes:
> 
> > We call perf_adjust_freq() from perf_counter_task_tick() which is is called
> > under the rq->lock causing lock recursion.
> 
> What was the lock recursion?  I see perf_adjust_freq taking ctx->lock,
> but we were careful not to take any rq->lock within a ctx->lock, at
> least in the past.

perf_output_end() can end up calling a wake_up().

perf_output_end()
  perf_output_unlock()
    perf_output_wakeup()
      perf_counter_wakeup()
        wake_up_all();