Re: [PATCH] Revert "net: linkwatch: add check for netdevice being present to linkwatch_do_dev"

[David Miller]

From: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
Date: Tue,  1 Sep 2020 17:02:37 +0200

> This reverts commit 124eee3f6955f7aa19b9e6ff5c9b6d37cb3d1e2c.
> 
> Inami-san reported that this commit breaks bridge support in a Xen
> environment, and that reverting it fixes this.
> 
> During system resume, bridge ports are no longer enabled, as that relies
> on the receipt of the NETDEV_CHANGE notification.  This notification is
> not sent, as netdev_state_change() is no longer called.
> 
> Note that the condition this commit intended to fix never existed
> upstream, as the patch triggering it and referenced in the commit was
> never applied upstream.  Hence I can confirm s2ram on r8a73a4/ape6evm
> and sh73a0/kzm9g works fine before/after this revert.
> 
> Reported-by Gaku Inami <gaku.inami.xh@xxxxxxxxxxx>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>

Maybe you cannot reproduce it, but the problem is there and it still
looks very real to me.

netdev_state_change() does two things:

1) Emit the NETDEV_CHANGE notification

2) Emit an rtmsg_ifinfo() netlink message, which in turn tries to access
   the device statistics via ->ndo_get_stats*().

It is absolutely wrong to do #2 when netif_device_present() is false.

So I cannot apply this patch as-is, sorry.