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From: Stephen Hemminger <stephen@networkplumber.org>
To: Thomas Monjalon <thomas@monjalon.net>
Cc: Ferruh Yigit <ferruh.yigit@intel.com>, dev@dpdk.org, stable@dpdk.org
Subject: Re: [dpdk-stable] [dpdk-dev] [PATCH] kni: fix kernel deadlock when using mlx devices
Date: Tue, 5 May 2020 17:14:54 -0700
Message-ID: <20200505171454.00274f10@hermes.lan> (raw)
In-Reply-To: <3101970.h16uAIiOU7@xps>

On Wed, 18 Mar 2020 16:17:57 +0100
Thomas Monjalon <thomas@monjalon.net> 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: stable@dpdk.org
> > > Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> > > ---  
> > 
> > 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

  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 [this message]
2020-07-27 17:33       ` Ferruh Yigit
2020-07-27 17:52         ` Stephen Hemminger
2020-07-28  8:56           ` Igor Ryzhov

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