https://bugs.freedesktop.org/show_bug.cgi?id=93911
--- Comment #8 from David Breese dabreese00@gmail.com --- Thank you very much for pointing me to that, it looks right. I didn't manage to find it when searching the bug tracker.
I've now upgraded to kernel 4.4 which contains the relevant commit. No more crashes so far after 3 days of heavy use -- normally I would have expected a crash sometime.
I'll post back if I do see the crash again, but provisionally I'll say this did the trick.
Thanks!