netdev - Re: rtnl_lock deadlock on 3.10

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Date:	Tue, 30 Jul 2013 07:54:42 -0500
From:	Steve Wise <swise@...ngridcomputing.com>
To:	Shawn Bohrer <sbohrer@...advisors.com>
CC:	Or Gerlitz <ogerlitz@...lanox.com>,
	Shawn Bohrer <shawn.bohrer@...il.com>,
	Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org,
	linux-rdma@...r.kernel.org, roland@...estorage.com,
	swise@...lsio.com
Subject: Re: rtnl_lock deadlock on 3.10

On 7/29/2013 6:02 PM, Shawn Bohrer wrote:
> On Mon, Jul 15, 2013 at 09:38:19AM -0500, Shawn Bohrer wrote:
>> On Wed, Jul 03, 2013 at 08:26:11PM +0300, Or Gerlitz wrote:
>>> On 03/07/2013 20:22, Shawn Bohrer wrote:
>>>> 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
>>>>
>>> Guys, I was a bit busy today looking into that, but I don't think we
>>> want the IB core layer  (core/device.c) to
>>> use rtnl locking which is something that belongs to the network stack.
>> Has anymore thought been put into a proper fix for this issue?
> I'm no expert in this area but I'm having a hard time seeing a
> different solution than the one Cong suggested.  Just to be clear the
> deadlock I hit was between cxgb3 and the ipoib module, so I've Cc'd
> Steve Wise in case he has a better solution from the Chelsio side.

I don't know of another way to resolve this.   The rtnl lock is used in 
ipoib and mlx4 already.  I think we should go forward with the proposed 
patch.

Steve.

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