while running this new test during review process, I see a vpp crash.

https://gerrit.fd.io/r/#/c/4429/

Testing with version 4 of the patch:

git fetch https://gerrit.fd.io/r/vpp refs/changes/29/4429/4 && git
checkout FETCH_HEAD

rebased on top of ce1aae4e88d8ed2c73e8213115cf9f3a4e37370f

command to run the test was

make test TEST=ip4_vrf_multi_instance V=2

it doesn't always crash, but it seems to be common enough

Stack:

(gdb) bt
#0 0x00007fe7f84f8428 in __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:54
#1 0x00007fe7f84fa02a in __GI_abort () at abort.c:89
#2 0x0000000000406f79 in os_exit (code=code@entry=1) at /home/ksekera/vpp/build-data/../src/vpp/vnet/main.c:354
#3 0x00007fe7f9dec6ca in unix_signal_handler (signum=<optimized out>, si=<optimized out>, uc=<optimized out>)
at /home/ksekera/vpp/build-data/../src/vlib/unix/main.c:115
#4 <signal handler called>
#5 vlib_buffer_free_inline (follow_buffer_next=1, n_buffers=<optimized out>, buffers=<optimized out>, vm=0x7fe7fa0021a0 <vlib_global_main>,
vm@entry=0x7fe7b8dcf370) at /home/ksekera/vpp/build-data/../src/vlib/buffer.c:1214
#6 vlib_buffer_free (vm=vm@entry=0x7fe7fa0021a0 <vlib_global_main>, buffers=buffers@entry=0x7fe7b8dc9b10, n_buffers=<optimized out>)
at /home/ksekera/vpp/build-data/../src/vlib/buffer.c:1324
#7 0x00007fe7f97f84cc in process_drop_punt (disposition=VNET_ERROR_DISPOSITION_DROP, frame=0x7fe7b8dc9b00, node=<optimized out>,
vm=<optimized out>) at /home/ksekera/vpp/build-data/../src/vnet/interface_output.c:1030
#8 process_drop (frame=<optimized out>, node=<optimized out>, vm=<optimized out>)
at /home/ksekera/vpp/build-data/../src/vnet/interface_output.c:1117
#9 process_drop_avx2 (vm=<optimized out>, node=<optimized out>, frame=<optimized out>)
at /home/ksekera/vpp/build-data/../src/vnet/interface_output.c:1138
#10 0x00007fe7f9db3699 in dispatch_node (vm=0x7fe7fa0021a0 <vlib_global_main>, node=0x7fe7b82dd5c0, type=<optimized out>,
dispatch_state=VLIB_NODE_STATE_POLLING, frame=<optimized out>, last_time_stamp=5124515270893)
at /home/ksekera/vpp/build-data/../src/vlib/main.c:998
#11 0x00007fe7f9db3a35 in dispatch_pending_node (vm=vm@entry=0x7fe7fa0021a0 <vlib_global_main>, p=0x7fe7b94160d8, last_time_stamp=<optimized out>)
at /home/ksekera/vpp/build-data/../src/vlib/main.c:1136