linux-kernel - Re: cpu_hotplug vs oom_notify_list: possible circular locking dependency detected

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Message-ID: <alpine.DEB.2.10.1507161401320.14938@chino.kir.corp.google.com>
Date:	Thu, 16 Jul 2015 14:01:56 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
cc:	Marcin Ślusarz <marcin.slusarz@...il.com>,
	Tejun Heo <tj@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org
Subject: Re: cpu_hotplug vs oom_notify_list: possible circular locking
 dependency detected

On Wed, 15 Jul 2015, Paul E. McKenney wrote:

> On Tue, Jul 14, 2015 at 04:48:24PM -0700, David Rientjes wrote:
> > On Tue, 14 Jul 2015, Paul E. McKenney wrote:
> > 
> > > commit a1992f2f3b8e174d740a8f764d0d51344bed2eed
> > > Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > > Date:   Tue Jul 14 16:24:14 2015 -0700
> > > 
> > >     rcu: Don't disable CPU hotplug during OOM notifiers
> > >     
> > >     RCU's rcu_oom_notify() disables CPU hotplug in order to stabilize the
> > >     list of online CPUs, which it traverses.  However, this is completely
> > >     pointless because smp_call_function_single() will quietly fail if invoked
> > >     on an offline CPU.  Because the count of requests is incremented in the
> > >     rcu_oom_notify_cpu() function that is remotely invoked, everything works
> > >     nicely even in the face of concurrent CPU-hotplug operations.
> > >     
> > >     Furthermore, in recent kernels, invoking get_online_cpus() from an OOM
> > >     notifier can result in deadlock.  This commit therefore removes the
> > >     call to get_online_cpus() and put_online_cpus() from rcu_oom_notify().
> > >     
> > >     Reported-by: Marcin Ślusarz <marcin.slusarz@...il.com>
> > >     Reported-by: David Rientjes <rientjes@...gle.com>
> > >     Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > 
> > Acked-by: David Rientjes <rientjes@...gle.com>
> 
> Thank you!
> 
> Any news on whether or not it solves the problem?
> 

Marcin, is your lockdep violation reproducible?  If so, does this patch 
fix it?