kern/56900: panic in uvm_map_findspace

[Thomas Klausner <wiz%NetBSD.org@localhost>]

>Number:         56900
>Category:       kern
>Synopsis:       panic in uvm_map_findspace
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Jun 24 17:45:00 +0000 2022
>Originator:     Thomas Klausner
>Release:        NetBSD 9.99.98
>Organization:

>Environment:
	
	
Architecture: x86_64
Machine: amd64
>Description:
Before the UVM changes from early June 2022, my system was stable.
Afterwards, when bulk building, I usually have about a panic after a couple hours, the last one
had this back trace:

panic: kernel diagnostic assertion â??!topdown || hint <= orig_hintâ?? failed: file â??/usr/src/sys/uvm/uvm_map.câ??, line 1795 map=0xffffc8415a1d9388 hint=0xfffffff944a00000 orig_hint=0x82000000 length=0x77e000000 uobj=0x0 uoffset=0xfffffffffffffffff align=0 flags=0x80710 entry=0xffffc8415a1d93e0 (uvm_map_findspace line 1998)
cpu0: begin traceback
vpanic()
kern_assert()
uvm_findspace_invariants() at netbsd:uvm_findspace_invariants+0x83
uvm_map_findspace() at netbsd:uvm_map_findspace()+0x1c6
uvm_map_prepare() at netbsd:uvm_map_prepare+0x1f6
uvm_map() at netbsd:uvm_map+0x70
uvm_mmap.part.0() at netbsd:vm_mmap.part.0+0x15a
sys_mmap() at netbsd:sys_mmap+0x42f
syscall() number 197

(Handcopied with autocorrection, but I have pictures if you want to verify something).


>How-To-Repeat:
Boot 9.99.98, start bulk build.
>Fix:
Backing out the changes makes the system stable again, but riastradh thinks this
might be just papering over an underlying (benign?) problem the new assertion detects.

>Unformatted: