root@a20:~ # uname -a

FreeBSD a20 11.0-CURRENT FreeBSD 11.0-CURRENT #0 r297692: Fri Apr  8 07:10:09 UTC 2016     root@releng2.nyi.freebsd.org:/usr/obj/arm.armv6/usr/src/sys/A20  arm
root@a20:~ # tar cf /dev/null /usr

tar: Removing leading '/' from member names
panic: vm_page_insert_after: page already inserted
cpuid = 0
KDB: enter: panic
[ thread pid 524 tid 100056 ]
Stopped at      $d.6:   ldrb    r15, [r15, r15, ror r15]!
db> bt
Tracing pid 524 tid 100056 td 0xc42996e0
db_trace_self() at db_trace_self
         pc = 0xc06861a4  lr = 0xc0249ae8 (db_stack_trace+0x108)
         sp = 0xef69a5c0  fp = 0xef69a5d8
db_stack_trace() at db_stack_trace+0x108
         pc = 0xc0249ae8  lr = 0xc024972c (db_command+0x270)
         sp = 0xef69a5e0  fp = 0xef69a680
         r4 = 0x00000001  r5 = 0x00000000
         r6 = 0xc071ea98 r10 = 0xc0939ccc
db_command() at db_command+0x270
         pc = 0xc024972c  lr = 0xc02494ac (db_command_loop+0x74)
         sp = 0xef69a688  fp = 0xef69a698
         r4 = 0xc06f2711  r5 = 0xc071712d
         r6 = 0xc0939cb8  r7 = 0xef69a868
         r8 = 0xc08d2280  r9 = 0xc07e3b78
        r10 = 0xc08d2284
db_command_loop() at db_command_loop+0x74
         pc = 0xc02494ac  lr = 0xc024c1a8 (db_trap+0x120)
         sp = 0xef69a6a0  fp = 0xef69a7b8
         r4 = 0x00000001  r5 = 0x00000000
--More--
         r6 = 0xc0939cc4 r10 = 0xc08d2284
db_trap() at db_trap+0x120
         pc = 0xc024c1a8  lr = 0xc0419450 (kdb_trap+0x180)
         sp = 0xef69a7c0  fp = 0xef69a7e8
         r4 = 0x00000000  r5 = 0x00000001
         r6 = 0xc08d22a0 r10 = 0xc08d2284
kdb_trap() at kdb_trap+0x180
         pc = 0xc0419450  lr = 0xc06a4f3c (undefinedinstruction+0x318)
         sp = 0xef69a7f0  fp = 0xef69a860
         r4 = 0x00000000  r5 = 0x00000000
         r6 = 0xc06a4b74  r7 = 0xe7ffffff
         r8 = 0xc42996e0  r9 = 0xc0418b7c
        r10 = 0xef69a868
undefinedinstruction() at undefinedinstruction+0x318
         pc = 0xc06a4f3c  lr = 0xc0688fac (exception_exit)
         sp = 0xef69a868  fp = 0xef69a900
         r4 = 0xa00000d3  r5 = 0xc42996e0
         r6 = 0xc0747d41  r7 = 0x00000001
         r8 = 0xef69a94c  r9 = 0xc093babc
        r10 = 0xc08c2020
--More--        
exception_exit() at exception_exit
         pc = 0xc0688fac  lr = 0xc0418b6c (kdb_enter+0x48)
         sp = 0xef69a8f8  fp = 0xef69a900
         r0 = 0xc08d2294  r1 = 0x00000000
         r2 = 0xef69a834  r3 = 0x00000213
         r4 = 0xc071708a  r5 = 0xc42996e0
         r6 = 0xc0747d41  r7 = 0x00000001
         r8 = 0xef69a94c  r9 = 0xc093babc
        r10 = 0xc08c2020 r12 = 0x20000000
$a.7() at $a.7
         pc = 0xc0418b80  lr = 0xc03d9134 (vpanic+0x160)
         sp = 0xef69a908  fp = 0xef69a928
         r4 = 0x00000100 r10 = 0xc08c2020
vpanic() at vpanic+0x160
         pc = 0xc03d9134  lr = 0xc03d8fd4 (vpanic)
         sp = 0xef69a930  fp = 0xef69a944
         r4 = 0xc0747d41  r5 = 0xef69a94c
         r6 = 0xc12370e0  r7 = 0xc093f974
         r8 = 0xc1237130  r9 = 0x00031222
        r10 = 0x00000000
--More--        
vpanic() at vpanic
         pc = 0xc03d8fd4  lr = 0xc066baec (vm_page_insert_after+0x130)
         sp = 0xef69a94c  fp = 0xef69a978
         r4 = 0xef69a944  r5 = 0xc03d8fd4
         r6 = 0xef69a94c  r7 = 0xc5500b28
         r8 = 0x00000045  r9 = 0xc12370e0
        r10 = 0x00000000
vm_page_insert_after() at vm_page_insert_after+0x130
         pc = 0xc066baec  lr = 0xc066ce3c (vm_page_alloc+0x570)
         sp = 0xef69a980  fp = 0xef69a9b0
         r4 = 0x00000000  r5 = 0xc093f974
         r6 = 0xc1237130  r7 = 0xc093f974
         r8 = 0x00000020  r9 = 0x00031222
        r10 = 0xc5500b28
vm_page_alloc() at vm_page_alloc+0x570
         pc = 0xc066ce3c  lr = 0xc066ff00 (vm_page_grab+0x18c)
         sp = 0xef69a9b8  fp = 0xef69a9f0
         r4 = 0xc0747256  r5 = 0x00000045
         r6 = 0x00001222  r7 = 0xc5500b38
         r8 = 0x00000008  r9 = 0x00000000
--More--        
        r10 = 0x00000000
vm_page_grab() at vm_page_grab+0x18c
         pc = 0xc066ff00  lr = 0xc04764e8 (allocbuf+0x2f0)
         sp = 0xef69a9f8  fp = 0xef69aa38
         r4 = 0x00008000  r5 = 0xd9275b70
         r6 = 0x00001222  r7 = 0xc5500b28
         r8 = 0x00000008  r9 = 0xd9275ba0
        r10 = 0xd9275b70
allocbuf() at allocbuf+0x2f0
         pc = 0xc04764e8  lr = 0xc04742f8 (getblk+0x8fc)
         sp = 0xef69aa40  fp = 0xef69aab0
         r4 = 0x00008000  r5 = 0x00000008
         r6 = 0x00008000  r7 = 0x00008000
         r8 = 0xc55071a4  r9 = 0x00000008
        r10 = 0xd9275b70
getblk() at getblk+0x8fc
         pc = 0xc04742f8  lr = 0xc04750e8 (breadn_flags+0x34)
         sp = 0xef69aab8  fp = 0xef69aae8
         r4 = 0x00008000  r5 = 0xc5507120
         r6 = 0x0000748e  r7 = 0x0000748e
--More--        
         r8 = 0x00000009  r9 = 0xffffffef
        r10 = 0xc5507120
breadn_flags() at breadn_flags+0x34
         pc = 0xc04750e8  lr = 0xc0636ff4 ($a.1+0x5f8)
         sp = 0xef69aaf0  fp = 0xef69ab90
         r4 = 0x00008000  r5 = 0x0000000f
         r6 = 0x0000748e  r7 = 0x0000748e
         r8 = 0x00000009  r9 = 0xffffffef
        r10 = 0xc5507120
$a.1() at $a.1+0x5f8
         pc = 0xc0636ff4  lr = 0xc06c1714 (VOP_READ_APV+0x128)
         sp = 0xef69ab98  fp = 0xef69abb0
         r4 = 0xef69abc0  r5 = 0xc08294e8
         r6 = 0x00000000  r7 = 0xef69abc4
         r8 = 0x00000000  r9 = 0xef69adc0
        r10 = 0x00040000
VOP_READ_APV() at VOP_READ_APV+0x128
         pc = 0xc06c1714  lr = 0xc04a26e8 (vn_read+0x150)
         sp = 0xef69abb8  fp = 0xef69ac00
         r4 = 0xc5507120  r5 = 0xc42a1400
--More--        
         r6 = 0xef69adc8  r7 = 0x00000000
vn_read() at vn_read+0x150
         pc = 0xc04a26e8  lr = 0xc04a2544 (vn_io_fault_doio+0x88)
         sp = 0xef69ac08  fp = 0xef69ac28
         r4 = 0xc04a2598  r5 = 0xef69add0
         r6 = 0xc41efec0  r7 = 0x00000000
         r8 = 0xef69ad08  r9 = 0xfbffff7f
        r10 = 0xef69adc0
vn_io_fault_doio() at vn_io_fault_doio+0x88
         pc = 0xc04a2544  lr = 0xc04a03f0 (vn_io_fault1+0x1a0)
         sp = 0xef69ac30  fp = 0xef69acf0
         r4 = 0xc42996e0 r10 = 0xef69adc0
vn_io_fault1() at vn_io_fault1+0x1a0
         pc = 0xc04a03f0  lr = 0xc049ea84 ($a.1+0x1b0)
         sp = 0xef69acf8  fp = 0xef69ad38
         r4 = 0x00000000  r5 = 0xc42a1400
         r6 = 0xef69adc0  r7 = 0xc5507174
         r8 = 0xc42bf000  r9 = 0x00000000
        r10 = 0xc55071f8
$a.1() at $a.1+0x1b0
--More--        
         pc = 0xc049ea84  lr = 0xc043aae8 (dofileread+0xb0)
         sp = 0xef69ad40  fp = 0xef69ad68
         r4 = 0xc42996e0  r5 = 0xc049e8d4
         r6 = 0xef69adc0  r7 = 0xc42a1400
         r8 = 0x00000000  r9 = 0x00000000
        r10 = 0x0000748e
dofileread() at dofileread+0xb0
         pc = 0xc043aae8  lr = 0xc043a7ec (kern_readv+0x78)
         sp = 0xef69ad70  fp = 0xef69adb0
         r4 = 0xffffffff  r5 = 0x00000000
         r6 = 0x00000000  r7 = 0x00000007
         r8 = 0xef69adc0  r9 = 0xc42996e0
        r10 = 0x208771b8
kern_readv() at kern_readv+0x78
         pc = 0xc043a7ec  lr = 0xc043a760 (sys_read+0x4c)
         sp = 0xef69adb8  fp = 0xef69ade0
         r4 = 0xc42996e0  r5 = 0xc3e8c720
         r6 = 0x00000000  r7 = 0xc093b708
         r8 = 0x00000000  r9 = 0xef69adf8
sys_read() at sys_read+0x4c
--More--        
         pc = 0xc043a760  lr = 0xc06a3c48 (swi_handler+0x330)
         sp = 0xef69ade8  fp = 0xef69ae48
swi_handler() at swi_handler+0x330
         pc = 0xc06a3c48  lr = 0xc0688f3c (swi_exit)
         sp = 0xef69ae50  fp = 0xbfbfeae0
         r4 = 0x00000000  r5 = 0x00000007
         r6 = 0x20811000  r7 = 0x00000003
         r8 = 0x0000748e  r9 = 0x0000748e
        r10 = 0x208771b8
swi_exit() at swi_exit
         pc = 0xc0688f3c  lr = 0xc0688f3c (swi_exit)
         sp = 0xef69ae50  fp = 0xbfbfeae0
db>