linux-kernel - Re: rcu: endless stalls

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Message-ID: <20120611165413.GC2521@linux.vnet.ibm.com>
Date:	Mon, 11 Jun 2012 09:54:13 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Mike Galbraith <mgalbraith@...ell.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: rcu: endless stalls

On Mon, Jun 11, 2012 at 04:22:23PM +0200, Mike Galbraith wrote:
> 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.

Which clearly demands the question "why not increase the serial-console
baud rate"...  ;-)

							Thanx, Paul

> > 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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