Panic in uvm_anon.c (amd64)

[Julio Merino <jmmv%julipedia.org@localhost>]

Hello,

I just found the following amd64 -current crash on my virtual machine 
while building a set of packages.  (Yes, this is related to my other gdb 
thread, but posting separately because they are different issues.)

Aug 17 16:28:10 netbsd /netbsd: panic: kernel diagnostic assertion 
"anon->an_page == NULL" failed: file 
"/home/jmmv/os/netbsd/src/sys/uvm/uvm_anon.c", line 202
Aug 17 16:28:10 netbsd /netbsd: cpu0: Begin traceback...
Aug 17 16:28:10 netbsd /netbsd: kern_assert() at netbsd:kern_assert+0x2d
Aug 17 16:28:10 netbsd /netbsd: uvm_anon_free() at netbsd:uvm_anon_free+0xa8
Aug 17 16:28:10 netbsd /netbsd: uvm_anon_freelst() at 
netbsd:uvm_anon_freelst+0x194
Aug 17 16:28:10 netbsd /netbsd: amap_wipeout() at netbsd:amap_wipeout+0x12b
Aug 17 16:28:10 netbsd /netbsd: uvm_unmap_detach() at 
netbsd:uvm_unmap_detach+0x4a
Aug 17 16:28:10 netbsd /netbsd: uvmspace_free() at netbsd:uvmspace_free+0xf8
Aug 17 16:28:10 netbsd /netbsd: exit1() at netbsd:exit1+0x188
Aug 17 16:28:10 netbsd /netbsd: sys_exit() at netbsd:sys_exit+0x3e
Aug 17 16:28:10 netbsd /netbsd: syscall() at netbsd:syscall+0xa9
Aug 17 16:28:10 netbsd /netbsd: cpu0: End traceback...
Aug 17 16:28:10 netbsd /netbsd:
Aug 17 16:28:10 netbsd /netbsd: dumping to dev 0,1 offset 2025

Has anybody seen anything similar?  Is it worth sending a PR?

Thanks.