Comment 8 for bug 1534345

Hi Will and thanks for volunteering. That backtrace at least looks to confirm the educated guess about being related to network. *If* it actually is related, then I could imagine that processing incoming network traffic in softirq context of cpu#1 might cancel a timer which was set to wait for a packet to arrive and maybe that at or around the same time expired. Still hard to say for sure.
Looking at the xen-netfont driver between 3.19 and 4.2 there was not any change that stuck out as suspicious but then it might as well be a change in the network stack which the xen driver would need to adapt for.
About the mainline kernels. While I never would *promise* nothing horrible to happen, I would not expect anything so bad that there was not a chance to switch back to a different kernel. The mainline kernels miss some of the few special drivers (mostly overlayfs) which I don't think you have in use. As you say 3.19 is ok, I would suggest to go for 4.0.9 first and 4.1.15 after that. Both contain the latest upstream stable patches.