Yes this is a kernel bug. It was reported at
https://groups.google.com/forum/#!msg/syzkaller-bugs/1Z4Sn5KhBWI/3EG8ktCPBQAJ.
Presumably it's blocking upstream testing at the moment.
Most bugs are dependent on specific kernel config options, which can be disabled
to make the bugs unreachable. But why bother finding bugs if not to fix them?
You can help by helping to fix this bug. For example, bisect to find which
commit introduced the bug, and let the appropriate people / mailing lists know
what you found. And if possible, send a patch to fix the bug.
- Eric