kern/54419: mbuf leak when deleting route

[sc.dying%gmail.com@localhost]

>Number:         54419
>Category:       kern
>Synopsis:       mbuf leak when deleting route
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jul 29 08:35:00 +0000 2019
>Originator:     sc.dying%gmail.com@localhost
>Release:        NetBSD 8.99.51
>Organization:
>Environment:
System: NetBSD  8.99.51 NetBSD 8.99.51 (GENERIC) #0: Sun Jul 28 17:41:21 UTC 2019  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64 x86_64
>Description:

An mbuf goes somewhere when deleting a route on -current/amd64 and -8.1/amd64.

When you delete a route using route command, it is deleted successfully, but
mbuf usage of netstat -m gains 1.
See How-To-Repeat for detail.

I saw same problem on NetBSD-8.1/amd64, too.

>How-To-Repeat:

After boot single, I typed following commands.

# uname -ap
NetBSD  8.99.51 NetBSD 8.99.51 (GENERIC) #0: Sun Jul 28 17:41:21 UTC 2019  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64 x86_64
# ifconfig lo0 127.0.0.1
# route add 192.168.0.1 127.0.0.1
add host 192.168.0.1: gateway 127.0.0.1
# netstat -m
0 mbufs in use:
0 calls to protocol drain routines
# route delete 192.168.0.1
delete host 192.168.0.1
# netstat -m
1 mbufs in use:
        1 mbufs allocated to data
0 calls to protocol drain routines
# sh -c 'i=0; while [ $i -lt 10000 ]; do route -q add 192.168.0.1 127.0.0.1; route -q delete 192.168.0.1; i=$((i+1)); done'
# netstat -m
10001 mbufs in use:
        10001 mbufs allocated to data
0 calls to protocol drain routines
#

>Fix:
	Yes, please.