netdev - Re: [PATCH net v2] openvswitch: fix a possible deadlock and lockdep warning

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Message-ID: <20140327173344.GK18707@t520.home>
Date:	Thu, 27 Mar 2014 14:33:44 -0300
From:	Flavio Leitner <fbl@...hat.com>
To:	Pravin Shelar <pshelar@...ira.com>
Cc:	Jesse Gross <jesse@...ira.com>, netdev <netdev@...r.kernel.org>,
	openvswitch <dev@...nvswitch.org>
Subject: Re: [PATCH net v2] openvswitch: fix a possible deadlock and lockdep
 warning

On Thu, Mar 27, 2014 at 10:19:23AM -0700, Pravin Shelar wrote:
> On Thu, Mar 27, 2014 at 7:05 AM, Flavio Leitner <fbl@...hat.com> wrote:
> > There are two problematic situations.
> >
> > A deadlock can happen when is_percpu is false because it can get
> > interrupted while holding the spinlock. Then it executes
> > ovs_flow_stats_update() in softirq context which tries to get
> > the same lock.
> >
> > The second sitation is that when is_percpu is true, the code
> > correctly disables BH but only for the local CPU, so the
> > following can happen when locking the remote CPU without
> > disabling BH:
> >
> >        CPU#0                            CPU#1
> >   ovs_flow_stats_get()
> >    stats_read()
> >  +->spin_lock remote CPU#1        ovs_flow_stats_get()
> >  |  <interrupted>                  stats_read()
> >  |  ...                       +-->  spin_lock remote CPU#0
> >  |                            |     <interrupted>
> >  |  ovs_flow_stats_update()   |     ...
> >  |   spin_lock local CPU#0 <--+     ovs_flow_stats_update()
> >  +---------------------------------- spin_lock local CPU#1
> >
> > This patch disables BH for both cases fixing the deadlocks.
> 
> This bug is already fixed in OVS.

Could you point me to the commit? I am not finding anything
recent.

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