linux-kernel - Re: mlockall triggred rcu

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Message-ID: <20130720140015.GA5860@linux.vnet.ibm.com>
Date:	Sat, 20 Jul 2013 07:00:15 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, kosaki.motohiro@...il.com, walken@...gle.com,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org
Subject: Re: mlockall triggred rcu_preempt stall.

On Fri, Jul 19, 2013 at 08:32:12PM -0400, Dave Jones wrote:
> On Fri, Jul 19, 2013 at 03:15:39PM -0700, Paul E. McKenney wrote:
>  > On Fri, Jul 19, 2013 at 10:53:23AM -0400, Dave Jones wrote:
>  > > My fuzz tester keeps hitting this. Every instance shows the non-irq stack
>  > > came in from mlockall.  I'm only seeing this on one box, but that has more
>  > > ram (8gb) than my other machines, which might explain it.
>  > 
>  > Are you building CONFIG_PREEMPT=n?  I don't see any preemption points in
>  > do_mlockall(), so a range containing enough vmas might well stall the
>  > CPU in that case.  
> 
> That was with full preempt.
> 
>  > Does the patch below help?  If so, we probably need others, but let's
>  > first see if this one helps.  ;-)
> 
> I'll try it on Monday.

Given full preempt, I wouldn't think that my patch would have any effect,
but look forward to hearing what happens.

Hmmm....  Were you running mlockall() concurrently from a bunch of
different processes sharing lots of memory via mmap() or some such?

							Thanx, Paul

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