patches for DPDK stable branches
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From: Ferruh Yigit <>
To: Stephen Hemminger <>,
	Thomas Monjalon <>
Subject: Re: [dpdk-stable] [dpdk-dev] [PATCH] kni: fix kernel deadlock when using mlx devices
Date: Mon, 27 Jul 2020 18:33:08 +0100
Message-ID: <> (raw)
In-Reply-To: <20200505171454.00274f10@hermes.lan>

On 5/6/2020 1:14 AM, Stephen Hemminger wrote:
> On Wed, 18 Mar 2020 16:17:57 +0100
> Thomas Monjalon <> wrote:
>> 17/01/2020 17:43, Ferruh Yigit:
>>> On 12/22/2019 5:55 PM, Stephen Hemminger wrote:  
>>>> This fixes a deadlock when using KNI with bifurcated drivers.
>>>> Bringing kni device up always times out when using Mellanox
>>>> devices.
>>>> The kernel KNI driver sends message to userspace to complete
>>>> the request. For the case of bifurcated driver, this may involve
>>>> an additional request to kernel to change state. This request
>>>> would deadlock because KNI was holding the RTNL mutex.
>>>> This was a bad design which goes back to the original code.
>>>> A workaround is for KNI driver to drop RTNL while waiting.
>>>> To prevent the device from disappearing while the operation
>>>> is in progress, it needs to hold reference to network device
>>>> while waiting.
>>>> As an added benefit, an useless error check can also be removed.
>>>> Fixes: 3fc5ca2f6352 ("kni: initial import")
>>>> Cc:
>>>> Signed-off-by: Stephen Hemminger <>
>>>> ---  
>>> This patch cause a hang on my server, not sure what exactly was the problem but
>>> kernel log was continuously printing "Cannot send to req_q". Will dig more.  
>> Ferruh, did you have a chance to check what is hanging?
>> Stephen, is there any news on your side?
> It did not hang when I tested it. The bug report is still open

Sorry for the delay, since I am working remotely I was worried about loosing the
connection to my server, finally I did create a virtual environment to test again.

I confirm the hang observed %100 when two different process updates the kni
interface, like two different process sets the mtu. Without this patch this
works fine.

I understand the motivation of the patch, but with change there is a possibility
to hang the server, which we can't allow, need to find another way. Can updating
mlx interface wait KNI interface operation to complete?

  reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-22 17:55 [dpdk-stable] " Stephen Hemminger
2020-01-17 16:43 ` Ferruh Yigit
2020-03-18 15:17   ` [dpdk-stable] [dpdk-dev] " Thomas Monjalon
2020-05-06  0:14     ` Stephen Hemminger
2020-07-27 17:33       ` Ferruh Yigit [this message]
2020-07-27 17:52         ` Stephen Hemminger
2020-07-28  8:56           ` Igor Ryzhov

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