Date: Tue, 26 Jun 2012 11:06:20 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Mike Galbraith <efault@gmx.de>
Cc: Alexey Vlasov <renton@renton.name>, linux-kernel@vger.kernel.org
Subject: Re: Attaching a process to cgroups
Message-ID: <20120626180620.GK2397@linux.vnet.ibm.com>
Reply-To: paulmck@linux.vnet.ibm.com
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On Thu, Jun 21, 2012 at 10:23:02AM +0200, Mike Galbraith wrote:
> On Thu, 2012-06-21 at 11:54 +0400, Alexey Vlasov wrote: 
> > On Wed, Jun 20, 2012 at 02:28:18PM +0200, Mike Galbraith wrote:
> > > 
> > > kernel/cgroup.c::cgroup_attach_task()
> > > {
> > > ...
> > > 	synchronize_rcu();
> > > ...
> > > }
> > 
> > So nothing can be done here? (I mean if only I knew how to fix it I
> > wouldn't ask about it ;)
> 
> Sure, kill the obnoxious thing, it's sitting right in the middle of the
> userspace interface.
> 
> I banged on it a while back (wrt explosive android patches), extracted
> RCU from the userspace interface.  It seemed to work great, much faster,
> couldn't make it explode.  I wouldn't bet anything I wasn't willing to
> immediately part with that the result was really really safe though ;-)

Or replace it with synchronize_rcu_expedited().  You can "get lucky"
for quite some time removing synchronize_rcu() calls!

							Thanx, Paul

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