linux-kernel - Re: [PATCH 1/7] perf_counter: fix dynamic irq

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Date:	Mon, 25 May 2009 09:19:52 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	John Kacur <jkacur@...hat.com>
Subject: Re: [PATCH 1/7] perf_counter: fix dynamic irq_period logging

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();



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