kern/55980: panic: kernel diagnostic assertion "atomic_load_relaxed...

[prlw1%cam.ac.uk@localhost]

>Number:         55980
>Category:       kern
>Synopsis:       panic:  kernel diagnostic assertion "atomic_load_relaxed...
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Feb 06 17:55:00 +0000 2021
>Originator:     Patrick Welche
>Release:        NetBSD-9.99.80/amd64
>Organization:
>Environment:
NetBSD 9.99.80 (GENERIC) #59: Sat Feb  6 13:13:44 GMT 2021               
total memory = 159 GB               
cpu23: AMD Opteron(tm) Processor 6174, id 0x100f91               

>Description:
Unfortunately all I have is from a tmux tip serial console:

[ 9916.0148407] panic: kernel diagnostic assertion "atomic_load_relaxed(&pp->pp 
[ 9916.0448418] cpu1: Begin traceback...                                        
[ 9916.0548410] vpanic() at netbsd:vpanic+0x156                                 
[ 9916.0648412] __x86_indirect_thunk_rax() at netbsd:__x86_indirect_thunk_rax   
[ 9916.0748414] pmap_clear_attrs() at netbsd:pmap_clear_attrs+0x124             
[ 9916.0948428] uvm_pagemarkdirty() at netbsd:uvm_pagemarkdirty+0x37b           
[ 9916.1048420] uao_get() at netbsd:uao_get+0x315                               
[ 9916.1148407] ubc_fault() at netbsd:ubc_fault+0x16a                           
[ 9916.1248414] uvm_fault_internal() at netbsd:uvm_fault_internal+0x57a         
[ 9916.1348416] trap() at netbsd:trap+0x5b7                                     
[ 9916.1448423] --- trap (number 6) ---                                         
[ 9916.1548415] copyin() at netbsd:copyin+0x2f                                  
[ 9916.1648407] uiomove() at netbsd:uiomove+0xba                                
[ 9916.1748414] ubc_uiomove() at netbsd:ubc_uiomove+0x157                       
[ 9916.1848421] tmpfs_write() at netbsd:tmpfs_write+0xff                        
[ 9916.1948418] VOP_WRITE() at netbsd:VOP_WRITE+0x40                            
[ 9916.2048415] vn_write() at netbsd:vn_write+0xe0                              
[ 9916.2148427] dofilewrite() at netbsd:dofilewrite+0x80                        
[ 9916.2248429] sys_write() at netbsd:sys_write+0x49                            
[ 9916.2348431] syscall() at netbsd:syscall+0x23e                               
[ 9916.2448428] --- syscall (number 4) ---                                      
[ 9916.2548430] netbsd:syscall+0x23e:                                           
[ 9916.2648437] cpu1: End traceback...                                          
[ 9916.2748425] rebooting...                                                    


>How-To-Repeat:

>Fix: