Date:	Thu, 05 Sep 2013 10:14:51 -0500
From:	Steve Wise <swise@...ngridcomputing.com>
To:	roland@...estorage.com
CC:	Bart Van Assche <bvanassche@....org>,
	Shawn Bohrer <sbohrer@...advisors.com>,
	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, swise@...lsio.com
Subject: Re: rtnl_lock deadlock on 3.10

On 9/5/2013 5:02 AM, Bart Van Assche wrote:
> On 07/30/13 14:54, Steve Wise wrote:
>> 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.
>
> (replying to an e-mail of one month ago)
>
> Hello,
>
> It would be appreciated if anyone could report what the current status 
> of this issue is. I think a deadlock I ran into with kernels 3.10 and 
> 3.11 and PCI pass-through is related to this issue. See also 
> http://bugzilla.kernel.org/show_bug.cgi?id=60856 for the lockdep report.
>
> Thanks,
>
> Bart.


Roland, what do you think?

As I've said, I think we should go ahead with using the rtnl lock in the 
core.  Is there a complete patch available for review?  looks like the 
original was a partial fix.

Steve.

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