Re: [PATCH net] net-sysfs: update the queue counts in the unregistration path

Quoting Jakub Kicinski (2021-12-01 16:05:13)

On Wed, 01 Dec 2021 10:32:01 +0100 Antoine Tenart wrote:

quoted

quoted

Would you mind pointing where in the code that happens? I can't seem 
to find anything looking at real_num_.x_queues outside dev.c and
net-sysfs.c :S  

The above trace was triggered using veths and this patch would solve
this as veths do use real_num_x_queues to fill 'struct ethtool_channels'
in its get_channels ops[1] which is then used to avoid making channel
counts updates if it is 0[2].

But when we are at line 175 in [2] we already updated the values from
the user space request at lines 144-151. This check validates the new
config so a transition from 0 -> n should not be prevented here AFAICT.

You're right. It worked in my testbed because I was not providing the
number of Rx channels with Ethtool, so channels.rx_counts wasn't updated
and still had the value veth provided. It "fixed" the issue for a
completely unrelated reason and obviously can't be a fix for the issue
described here. Thanks for having a second look at this, I completely
missed it...

Any way of fixing this is fine. If you ask me personally I'd probably
go with the ethtool fix to net and the zeroing and warn to net-next.
Unless I'm misreading and this fix does work, in which case your plan
is good, too.

I think you're right. Let's target net with the ethtool patch[1]. This
patch (still needed to keep track of the queue counts) and the warning
one can target net-next.

[1] And probably another one for the old ethtool ioctl interface too.

Thanks!
Antoine