Comment # 6 on bug 905900 from Oliver Neukum

(In reply to Martin Pluskal from comment #5)
> (In reply to Takashi Iwai from comment #3)
> > The message itself doesn't give any direct relation with the problem itself.
> > It's a generic message showing that there is a pending deferred work.
> > 
> > Could you check with kernel-debug flavor to get more debug prints?
> 
> # uname -r
> 4.0.0-rc6-2.g9064edc-debug
> 
> # modprobe usbnet msg_level=8
> # modprobe cdc_ether
> # wicked ifreload enp0s29f0u2
> # dmesg
> ...
> [  189.855307] cdc_ether 3-2:1.0 usb0: register 'cdc_ether' at
> usb-0000:00:1d.0-2, CDC Ethernet Device, e6:1f:13:5d:2f:cb
> [  189.855364] usbcore: registered new interface driver cdc_ether
> [  189.856568] cdc_ether 3-2:1.0 enp0s29f0u2: renamed from usb0
> [  217.323601] cdc_ether 3-2:1.0 enp0s29f0u2: open: enable queueing (rx 4,
> tx 4) mtu 1500 simple framing
> [  217.323670] cdc_ether 3-2:1.0 enp0s29f0u2: kevent 12 may have been dropped
> [  217.371989] cdc_ether 3-2:1.0 enp0s29f0u2: link speeds: 9728 kbps up,
> 9728 kbps down

You are seeing this due to commit b77e26d19, which introduced setting
promiscous mode. However the dmesg does not explain why work couldn't
scheduled. No other event is scheduled. Could you enable more debugging of work
queues themselves? Or please look for any other output of usbnet_defer_kevent()
in the log.