uvm_amap panic in -current

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

This happened on aarch64 -current while running a pkgsrc bulk build:

[ 346117.3280182] panic: kernel diagnostic assertion "amap->am_nused < amap->am_maxslot" failed: file "/home/source/ab/HEAD/src/sys/uvm/uvm_amap.c", line 1506
[ 346117.3380176] cpu4: Begin traceback...
[ 346117.3380176] trace fp ffffc0085a43fa10
[ 346117.3480181] fp ffffc0085a43fa30 vpanic() at ffffc000004b2fd4 netbsd:vpanic+0x15c
[ 346117.3580180] fp ffffc0085a43faa0 kern_assert() at ffffc000007d208c netbsd:kern_assert+0x5c
[ 346117.3580180] fp ffffc0085a43fb30 amap_add() at ffffc00000412b1c netbsd:amap_add+0x214
[ 346117.3680249] fp ffffc0085a43fb70 uvmfault_promote() at ffffc0000041833c netbsd:uvmfault_promote+0x174
[ 346117.3780191] fp ffffc0085a43fbd0 uvm_fault_internal() at ffffc00000419f70 netbsd:uvm_fault_internal+0xf78
[ 346117.3880182] fp ffffc0085a43fdf0 data_abort_handler() at ffffc0000008c754 netbsd:data_abort_handler+0x184
[ 346117.3980178] fp ffffc0085a43fe70 trap_el0_sync() at ffffc0000008bc6c netbsd:trap_el0_sync+0x27c
[ 346117.4080236] tf ffffc0085a43fed0 el0_trap() at ffffc00000089404 netbsd:el0_trap
[ 346117.4180252] ---- trapframe 0xffffc0085a43fed0 (304 bytes) ----
[ 346117.4180252]     pc=0000000200a4f5bc,   spsr=0000000020000000
[ 346117.4280366]    esr=0000000092000007,    far=0000f60326efaf98
[ 346117.4280366]     x0=0000000000000003,     x1=000000020114b000
[ 346117.4380257]     x2=0000000000000003,     x3=0000000000000008
[ 346117.4480252]     x4=0000000000000000,     x5=0000000000000000
[ 346117.4480252]     x6=0000ffffffd572d0,     x7=0000000000000000
[ 346117.4580251]     x8=0000000000000003,     x9=0000000000000000
[ 346117.4580251]    x10=0000000000000001,    x11=0000000000000000
[ 346117.4680282]    x12=0000000200000079,    x13=0000000000000000
[ 346117.4780348]    x14=0000f60327797c18,    x15=0000000000000000
[ 346117.4780348]    x16=000000020107b730,    x17=0000f6032d237100
[ 346117.4880322]    x18=0000000000000068,    x19=0000ffffffd57200
[ 346117.4880322]    x20=0000000000002698,    x21=0000f60326ef8900
[ 346117.4980323]    x22=0000f60326efaf98,    x23=000000000000000a
[ 346117.5080321]    x24=0000f603279ec340,    x25=0000f603276a8b00
[ 346117.5080321]    x26=0000f603279e7930,    x27=0000000200d92438
[ 346117.5180324]    x28=0000000000000000, fp=x29=0000ffffffd56fb0
[ 346117.5180324] lr=x30=0000000200a4fdd8,     sp=0000ffffffd56fb0
[ 346117.5280369] ------------------------------------------------
[ 346117.5380361] cpu4: End traceback...
Stopped in pid 20064.20064 (cc1plus) at netbsd:cpu_Debugger+0x4: 
ret