linux-kernel - Re: rcu: endless stalls

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Message-ID: <1339435214.7358.43.camel@marge.simpson.net>
Date:	Mon, 11 Jun 2012 19:20:14 +0200
From:	Mike Galbraith <mgalbraith@...ell.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Miklos Szeredi <mszeredi@...e.cz>
Subject: Re: rcu: endless stalls

On Mon, 2012-06-11 at 16:22 +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.

Gee, no wonder it took a while to emit the gripe, there were a few more
than 48 CPUs actually.. 4048 more to be precise.

4096 tasks on 4096 CPUs all hammering wait_lock at once r!pretty.

2aa15890 - mm: prevent concurrent unmap_mapping_range() on the same inode

-Mike

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