linux-kernel - Re: frequent softlockups with 3.10rc6.

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Date:	Wed, 19 Jun 2013 14:42:18 -0400
From:	Dave Jones <davej@...hat.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: frequent softlockups with 3.10rc6.

On Wed, Jun 19, 2013 at 11:13:02AM -0700, Paul E. McKenney wrote:

 > > On a whim, I reverted 971394f389992f8462c4e5ae0e3b49a10a9534a3
 > > (As I started seeing these just after that rcu merge).
 > > 
 > > It's only been 30 minutes, but it seems stable again. Normally I would
 > > hit these within 5 minutes.
 > > 
 > > I think this may be the same root cause for http://www.spinics.net/lists/kernel/msg1551503.html too.
 > 
 > In both cases, I am guessing that you built with CONFIG_PROVE_RCU_DELAY=y.

Yes.

 > Even then, this is very strange.  I am at a loss as to why udelay(200)
 > would result in a hang.

It may not be a real 'hang' per se, but might just be that that process isn't
scheduled within the time needed to appease the lockup detector ?
(20 seconds is a long time, but that box is under constant load when it's 
 running the fuzz tests, so.. ?)

 > Or does your system turn udelay() into something other than a pure spin?

I see no reason why it would. Am I missing something ?


I also don't know if it's related, but it would be real nice if someone
would push along that fix for rcu_preempt hogging the cpu when idle that's
been in timers/urgent for over a month.

	Dave

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