This stack trace is familiar, the netfront smartpoll feature is buggy
and so was disabled (this part is in the Debian kernel) but initial
attempts to allow it to be disabled were a bit buggy (the Debian kernel
is missing these fixes).
I'll pull in the additional patches:
fad2197bcb570350cb03c4ed789015baf0f86c81 xen/netfront: unconditionally initialize smartpoll hrtimer
00abe504c5cf268b73c45232aba56949af628349 xen/netfront: Fix another potential race condition
cb09635065163a933d0d00d077ddd9f0c0a908a1 Fix one race condition for netfront smartpoll logic
Ian.