em(4) stops forwarding

Hello,

I've been running CURRENT for long time and never experienced problem
with the built-in em(4) card before. Recently (I first noticed it on Jan
24) the card has stopped working several times. Nothing gets into the
log file. Carrier is still detected properly but no data is exchanged.
Ifconfig up/down doesn't help but kldunload/load does. When I run
tcpdump I don't see any packet coming in but I see some outgoing.

Can someone suggest what to look at when it happens the next time? I
have DDB compiled in. I will try to sniff the wire using another machine
next time to see if the card sends out anything.

The command 'pciconf -lv' says about the card this:
em0_at_pci2:1:0:   class=0x020000 card=0x05491014 chip=0x101e8086 rev=0x03
hdr=0x00
    vendor   = 'Intel Corporation'
    device   = '82540EP Gigabit Ethernet Controller (Mobile)'
    class    = network
    subclass = ethernet

The dmesg:
em0: <Intel(R) PRO/1000 Network Connection Version - 3.2.18> port
0x8000-0x803f mem 0xc0220000-0xc023ffff,0xc0200000-0xc020ffff irq 11 at
device 1.0 on pci2
em0: Ethernet address: 00:0d:60:cd:ae:e2
em0: [FAST]

The interrupt is shared since the machine is a notebook. I don't know if
it was just a coincidence but I think that it happened at the same time
as my USB mouse stopped working - the USB controller is on the same irq.

Michal