panic: PMAP_ISACTIVE
Stopped in mount_nfs at cpu_Debugger+0x4:       ret     zero,(ra)
db> t
cpu_Debugger() at cpu_Debugger+0x4
panic() at panic+0xfc
pmap_enter() at pmap_enter+0x188
uvm_fault() at uvm_fault+0x1634
trap() at trap+0x398
XentMM() at XentMM+0x20
--- memory management fault (from ipl 0) ---
pmap_activate() at pmap_activate+0x1e8
uvmspace_share() at uvmspace_share+0x64
uvm_fork() at uvm_fork+0x54
fork1() at fork1+0x720
kthread_create1() at kthread_create1+0x7c
nfs_getset_niothreads() at nfs_getset_niothreads+0x8c
mountnfs() at mountnfs+0x68
nfs_mount() at nfs_mount+0x1c4
sys_mount() at sys_mount+0x570
syscall() at syscall+0x1dc
XentSys() at XentSys+0x50
--- syscall (21, netbsd.sys_mount) ---
--- user mode ---