linux-kernel - Re: [PATCH RFC 0/4] Paravirtual spinlocks

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Date:	Wed, 9 Jul 2008 15:33:58 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Lameter <clameter@...ux-foundation.org>,
	Petr Tesarik <ptesarik@...e.cz>,
	Virtualization <virtualization@...ts.linux-foundation.org>,
	Xen devel <xen-devel@...ts.xensource.com>,
	Thomas Friebel <thomas.friebel@....com>,
	Avi Kivity <avi@...ranet.com>
Subject: Re: [PATCH RFC 0/4] Paravirtual spinlocks


the patches caused a boot hang with this config:

 http://redhat.com/~mingo/misc/config-Wed_Jul__9_14_47_04_CEST_2008.bad

i have bisected it down to:

  commit e17b58c2e85bc2ad2afc07fb8d898017c2b75ed1
  Author: Jeremy Fitzhardinge <jeremy@...p.org>
  Date:   Mon Jul 7 12:07:53 2008 -0700

      xen: implement Xen-specific spinlocks

i.e. applying that patch alone causes the hang. The hang happens in the 
ftrace self-test:

  initcall utsname_sysctl_init+0x0/0x19 returned 0 after 0 msecs
  calling  init_sched_switch_trace+0x0/0x4c
  Testing tracer sched_switch: PASSED
  initcall init_sched_switch_trace+0x0/0x4c returned 0 after 167 msecs
  calling  init_function_trace+0x0/0x12
  Testing tracer ftrace: 
  [hard hang]

it should have continued like this:

  Testing tracer ftrace: PASSED
  initcall init_function_trace+0x0/0x12 returned 0 after 198 msecs
  calling  init_irqsoff_tracer+0x0/0x14
  Testing tracer irqsoff: PASSED
  initcall init_irqsoff_tracer+0x0/0x14 returned 0 after 3 msecs
  calling  init_mmio_trace+0x0/0x12
  initcall init_mmio_trace+0x0/0x12 returned 0 after 0 msecs

note: ftrace is a user of raw spinlocks. Another speciality of the 
config is that it has paravirt enabled (obviously), and that it also has 
lock debugging enabled.

	Ingo
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