yet another uvm_amap panic

[Jared McNeill <jmcneill%invisible.ca@localhost>]

[ 37088.6770221] panic: kernel diagnostic assertion "amap->am_nused < amap->am_maxslot" failed: file "/home/source/ab/HEAD/src/sys/uvm/uvm_amap.c", line 1505
[ 37088.6870223] cpu4: Begin traceback...
[ 37088.6870223] trace fp ffffc0086e1d8a00
[ 37088.6970231] fp ffffc0086e1d8a20 vpanic() at ffffc000004b3eac netbsd:vpanic+0x15c
[ 37088.6970231] fp ffffc0086e1d8a90 kern_assert() at ffffc000007d2eec netbsd:kern_assert+0x5c
[ 37088.7070240] fp ffffc0086e1d8b20 amap_add() at ffffc000004143cc netbsd:amap_add+0x214
[ 37088.7170234] fp ffffc0086e1d8b60 uvmfault_promote() at ffffc00000419a7c netbsd:uvmfault_promote+0x174
[ 37088.7270239] fp ffffc0086e1d8bc0 uvm_fault_internal() at ffffc0000041b6b0 netbsd:uvm_fault_internal+0xf78
[ 37088.7370250] fp ffffc0086e1d8de0 data_abort_handler() at ffffc0000008e31c netbsd:data_abort_handler+0x184
[ 37088.7470247] fp ffffc0086e1d8e60 trap_el0_sync() at ffffc0000008d5bc netbsd:trap_el0_sync+0x35c
[ 37088.7570263] tf ffffc0086e1d8ed0 el0_trap() at ffffc0000008a924 netbsd:el0_trap
[ 37088.7570263] ---- trapframe 0xffffc0086e1d8ed0 (304 bytes) ----
[ 37088.7670355]     pc=0000000200a4f5bc,   spsr=0000000020000000
[ 37088.7770287]    esr=0000000092000007,    far=0000fe9bc0431fe0
[ 37088.7770287]     x0=0000000000000003,     x1=0000000201148000
[ 37088.7870299]     x2=0000000000000008,     x3=0000000000000001
[ 37088.7870299]     x4=0000000000000060,     x5=0000fe9bd8c1d888
[ 37088.7970293]     x6=0000ffffffbc0710,     x7=0000000000000000
[ 37088.8070290]     x8=0000000201148000,     x9=0000000201114000
[ 37088.8070290]    x10=0000000000000001,    x11=0000000000000001
[ 37088.8170281]    x12=000000000000000a,    x13=0000ffffffbbfef8
[ 37088.8170281]    x14=0000000000000240,    x15=0000000000000240
[ 37088.8270283]    x16=00000002010789f8,    x17=0000fe9bd97a7140
[ 37088.8270283]    x18=0000000000000010,    x19=0000ffffffbc06a8
[ 37088.8370282]    x20=000000000000e1e0,    x21=0000fe9bc0423e00
[ 37088.8470286]    x22=0000fe9bc0431fe0,    x23=000000000000000a
[ 37088.8470286]    x24=0000fe9bc2d8e1a0,    x25=0000000000000002
[ 37088.8570282]    x26=0000fe9bc4188ee0,    x27=0000000200d91060
[ 37088.8570282]    x28=0000000000000000, fp=x29=0000ffffffbc0490
[ 37088.8670287] lr=x30=0000000200a4f848,     sp=0000ffffffbc0490
[ 37088.8770281] ------------------------------------------------
[ 37088.8770281] cpu4: End traceback...