interface send-q stall in 6.99.40?

[Frank Kardel <kardel%netbsd.org@localhost>]

Hi,

I have two observations on 6.99.44 (amd64/evbarm) where a wm-interface 
send-queue is filled to the max. sendto()-calls terminate with ENOBUFS.

net.interfaces.wm3.sndq.len = 256
net.interfaces.wm3.sndq.maxlen = 256
net.interfaces.wm3.sndq.drops = 20007

the interface status is:
wm3: flags=8a43<UP,BROADCAST,RUNNING,ALLMULTI,SIMPLEX,MULTICAST> mtu 1500
        capabilities=7ff80<TSO4,IP4CSUM_Rx,IP4CSUM_Tx,TCP4CSUM_Rx>
        capabilities=7ff80<TCP4CSUM_Tx,UDP4CSUM_Rx,UDP4CSUM_Tx,TCP6CSUM_Rx>
        capabilities=7ff80<TCP6CSUM_Tx,UDP6CSUM_Rx,UDP6CSUM_Tx,TSO6>
        enabled=7ff80<TSO4,IP4CSUM_Rx,IP4CSUM_Tx,TCP4CSUM_Rx>
        enabled=7ff80<TCP4CSUM_Tx,UDP4CSUM_Rx,UDP4CSUM_Tx,TCP6CSUM_Rx>
        enabled=7ff80<TCP6CSUM_Tx,UDP6CSUM_Rx,UDP6CSUM_Tx,TSO6>
        ec_capabilities=7<VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU>
        ec_enabled=0
        address: 00:00:xx:xx:xx:xx
        media: Ethernet autoselect (1000baseT 
full-duplex,flowcontrol,master,rxpause,txpause)
        status: active
[addresses skipped]

traceroute packets from outside look like the are anwsered, but ICMP 
ECHO is not answered.

The interface recovers with an ifconfig wmX down/up.

While I do not know how to provoke this on wm (just happens once a 
week). I found the same phenomenon occurring on a Raspberry Pi when 
detaching the cable. The same symptoms occur there and ifconfig usmsc0 
down/up will recover.

Is anybody else seeing this?

Best regards,
  Frank