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Date: Fri, 13 May 2011 15:04:14 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Yinghai Lu <yinghai@kernel.org>
Cc: paulmck@linux.vnet.ibm.com, linux-kernel@vger.kernel.org
Subject: Re: [GIT PULL rcu/next] rcu commits for 2.6.40
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* Ingo Molnar <mingo@elte.hu> wrote:

> btw., i'm seeing a boot hang too, with the attached config:
> 
> PM: Adding info for platform:serial8250
> serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
> device: 'ttyS0': device_add
> PM: Adding info for No Bus:ttyS0
> INFO: rcu_sched_state detected stalls on CPUs/tasks: { 0} (detected by 1, t=6002 jiffies)
> INFO: rcu_sched_state detected stalls on CPUs/tasks: { 0} (detected by 1, t=24034 jiffies)
> INFO: rcu_sched_state detected stalls on CPUs/tasks: { 0} (detected by 1, t=42066 jiffies)
> INFO: rcu_sched_state detected stalls on CPUs/tasks: { 0} (detected by 1, t=6002 jiffies)
> INFO: rcu_sched_state detected stalls on CPUs/tasks: { 0} (detected by 1, t=24034 jiffies)
> 
> (and the stall warnings go on forever)

I started bisecting this, and the two relevant endpoints:

  bad: 11c476f: net,rcu: convert call_rcu(prl_entry_destroy_rcu) to kfree
 good: 0ee5623f: Linux 2.6.39-rc6

very clearly indicate that this is an RCU regression.

Thanks,

	Ingo