netdev - Re: [PATCH] wwan: core: Fix missing RTM

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Date:   Thu, 22 Jul 2021 20:42:07 +0300
From:   Sergey Ryazanov <ryazanov.s.a@...il.com>
To:     Loic Poulain <loic.poulain@...aro.org>
Cc:     David Miller <davem@...emloft.net>,
        Johannes Berg <johannes@...solutions.net>,
        Network Development <netdev@...r.kernel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH] wwan: core: Fix missing RTM_NEWLINK event

On Thu, Jul 22, 2021 at 7:44 PM Loic Poulain <loic.poulain@...aro.org> wrote:
> On Thu, 22 Jul 2021 at 18:14, Sergey Ryazanov <ryazanov.s.a@...il.com> wrote:
>> On Thu, Jul 22, 2021 at 6:39 PM Loic Poulain <loic.poulain@...aro.org> wrote:
>>> By default there is no rtnetlink event generated when registering a
>>> netdev with rtnl_link_ops until its rtnl_link_state is switched to
>>> initialized (RTNL_LINK_INITIALIZED). This causes issues with user
>>> tools like NetworkManager which relies on such event to manage links.
>>>
>>> Fix that by setting link to initialized (via rtnl_configure_link).
>>
>> Shouldn't the __rtnl_newlink() function call rtnl_configure_link()
>> just after the newlink() callback invocation? Or I missed something?
>
> Ah right, but the first call of rtnl_configure_link() (uninitialized)
> does not cause RTM_NEWLINK event (cf __dev_notify_flags). It however
> seems to work for other link types (e,g, rmnet), so probably something
> to clarify here.

Just check additional netdev creation with hwsim:

# ip link add wwan0.3 parentdev wwan0 type wwan linkid 3

On the other console:

# ip -d mon
6: wwan0.3: <POINTOPOINT,NOARP> mtu 1500 qdisc noop state DOWN group default
    link/none  promiscuity 0 minmtu 68 maxmtu 65535
    wwan numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535

But I saw no notification at the moment of wwan_hwsim module loading.
This happens since I missed the rtnl_configure_link() call in the
wwan_create_default_link() after the default link successful creation
:(

So we need your fix at least in the default link creation routine to
fix ca374290aaad ("wwan: core: support default netdev creation").
Something like this:

diff --git a/drivers/net/wwan/wwan_core.c b/drivers/net/wwan/wwan_core.c
index 3e16c318e705..374aa2cc884c 100644
--- a/drivers/net/wwan/wwan_core.c
+++ b/drivers/net/wwan/wwan_core.c
@@ -984,6 +984,8 @@ static void wwan_create_default_link(struct
wwan_device *wwandev,
  goto unlock;
  }

+ rtnl_configure_link(dev, NULL); /* trigger the RTM_NEWLINK event */
+
 unlock:
  rtnl_unlock();

--
Sergey