kern/56672: i915drmkms hangs on boot

[manu%netbsd.org@localhost]

>Number:         56672
>Category:       kern
>Synopsis:       i915drmkms hangs on boot
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Jan 26 10:30:00 +0000 2022
>Originator:     Emmanuel Dreyfus
>Release:        NetBSD 9.99.93
>Organization:
Emmanuel Dreyfus
manu%netbsd.org@localhost
>Environment:
NetBSD basalte 9.99.93 NetBSD 9.99.93 (GENERIC) #96: Fri Jan  7 05:54:04 CET 2022  manu@basalte:/home2/manu/netbsd-src/sys/arch/amd64/compile/GENERIC amd64
Architecture: x86_64
Machine: amd64
>Description:
Since the recent DRM upgrade, I randomly get hang at boot time in i915drmkms initialization. 

Initial investigation with ddb shows that the i915_flip kernel thread gets a corrupted backtrace. I suspect everyone is waiting on it to complete, but that will never happen because it crashed.
>How-To-Repeat:
Reboot and sometimes get hung
>Fix:
Not knwon yet