On Wed, 18 Mar 2020 16:17:57 +0100
Thomas Monjalon [off-list ref] wrote:

17/01/2020 17:43, Ferruh Yigit:

quoted

On 12/22/2019 5:55 PM, Stephen Hemminger wrote:  

quoted

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