The Xen Project CI has six machines which were affected by this regression. (Kernel messages are near-identical to those reported by others in this bug.) As suggested I downloaded this kernel;
https://people.debian.org/~benh/packages/jessie-pu/linux-image-3.16.0-4-amd64_3.16.51-3~a.test_amd64.deb and I can confirm that this fixes the issue. We will continue to use this kernel for the affected machines, until the next Debian point release (in which I hope this will be fixed). Thanks to Ben for the quick fix and to #debian-kernel for the pointer to the right bug report. Regards, Ian.
