netdev - Re: rtnl_lock deadlock on 3.10

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Message-ID: <20130703172239.GA3439@sbohrermbp13-local.rgmadvisors.com>
Date:	Wed, 3 Jul 2013 12:22:39 -0500
From:	Shawn Bohrer <shawn.bohrer@...il.com>
To:	Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org,
	linux-rdma@...r.kernel.org, roland@...estorage.com
Cc:	sbohrer@...advisors.com
Subject: Re: rtnl_lock deadlock on 3.10

On Wed, Jul 03, 2013 at 07:33:07AM +0200, Hannes Frederic Sowa wrote:
> On Wed, Jul 03, 2013 at 07:11:52AM +0200, Hannes Frederic Sowa wrote:
> > On Tue, Jul 02, 2013 at 01:38:26PM +0000, Cong Wang wrote:
> > > On Tue, 02 Jul 2013 at 08:28 GMT, Hannes Frederic Sowa <hannes@...essinduktion.org> wrote:
> > > > On Mon, Jul 01, 2013 at 09:54:56AM -0500, Shawn Bohrer wrote:
> > > >> I've managed to hit a deadlock at boot a couple times while testing
> > > >> the 3.10 rc kernels.  It seems to always happen when my network
> > > >> devices are initializing.  This morning I updated to v3.10 and made a
> > > >> few config tweaks and so far I've hit it 4 out of 5 reboots.  It looks
> > > >> like most processes are getting stuck on rtnl_lock.  Below is a boot
> > > >> log with the soft lockup prints.  Please let know if there is any
> > > >> other information I can provide:
> > > >
> > > > Could you try a build with CONFIG_LOCKDEP enabled?
> > > >
> > > 
> > > The problem is clear: ib_register_device() is called with rtnl_lock,
> > > but itself needs device_mutex, however, ib_register_client() first
> > > acquires device_mutex, then indirectly calls register_netdev() which
> > > takes rtnl_lock. Deadlock!
> > > 
> > > One possible fix is always taking rtnl_lock before taking
> > > device_mutex, something like below:
> > > 
> > > diff --git a/drivers/infiniband/core/device.c b/drivers/infiniband/core/device.c
> > > index 18c1ece..890870b 100644
> > > --- a/drivers/infiniband/core/device.c
> > > +++ b/drivers/infiniband/core/device.c
> > > @@ -381,6 +381,7 @@ int ib_register_client(struct ib_client *client)
> > >  {
> > >  	struct ib_device *device;
> > >  
> > > +	rtnl_lock();
> > >  	mutex_lock(&device_mutex);
> > >  
> > >  	list_add_tail(&client->list, &client_list);
> > > @@ -389,6 +390,7 @@ int ib_register_client(struct ib_client *client)
> > >  			client->add(device);
> > >  
> > >  	mutex_unlock(&device_mutex);
> > > +	rtnl_unlock();
> > >  
> > >  	return 0;
> > >  }
> > > diff --git a/drivers/infiniband/ulp/ipoib/ipoib_main.c b/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > > index b6e049a..5a7a048 100644
> > > --- a/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > > +++ b/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > > @@ -1609,7 +1609,7 @@ static struct net_device *ipoib_add_port(const char *format,
> > >  		goto event_failed;
> > >  	}
> > >  
> > > -	result = register_netdev(priv->dev);
> > > +	result = register_netdevice(priv->dev);
> > >  	if (result) {
> > >  		printk(KERN_WARNING "%s: couldn't register ipoib port %d; error %d\n",
> > >  		       hca->name, port, result);
> > 
> > Looks good to me. Shawn, could you test this patch?
> 
> ib_unregister_device/ib_unregister_client would need the same change,
> too. I have not checked the other ->add() and ->remove() functions. Also
> cc'ed linux-rdma@...r.kernel.org, Roland Dreier.

Cong's patch is missing the #include <linux/rtnetlink.h> but otherwise
I've had 34 successful reboots with no deadlocks which is a good sign.
It sounds like there are more paths that need to be audited and a
proper patch submitted.  I can do more testing later if needed.

Thanks,
Shawn
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