linux-kernel - Re: rcu: endless stalls

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Message-ID: <1339424543.7350.101.camel@marge.simpson.net>
Date:	Mon, 11 Jun 2012 16:22:23 +0200
From:	Mike Galbraith <mgalbraith@...ell.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: rcu: endless stalls

On Mon, 2012-06-11 at 06:39 -0700, Paul E. McKenney wrote: 
> On Mon, Jun 11, 2012 at 12:06:16PM +0200, Mike Galbraith wrote:
> > Greetings,
> > 
> > I received a report of a 48 core UV box hitting a gripe, taking longer
> > than timeout to emit same, so box griped endlessly, forcing reboot.
> 
> So it took minutes to print an RCU CPU stall warning?  On only 48 CPUs?
> 
> If so, yow!!!

The report was a tad fuzzy on details, but serial console can take a
while at low baud rate, and the box was apparently perma-stalled.

> My guess is that rcu_cpu_stall_suppress must be manipulated atomically
> for this to work reliably, for example, using xchg().

Ah, thanks.

-Mike

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