Fix for use-after-free in if_vlan.c

[• hselasky]

Summary

Running the script below triggers fault eventually. Not sure if the fix should be extended to cover more callback functions.

Test Plan

#!/usr/local/bin/bash
# Script to reproduce hang

for i in {1..255}
do
(ifconfig mce0.$i create; 
ifconfig mce0.$i inet 224.0.0.$i;
ifconfig mce0.$i destroy) &
done

[mjg]

is this waiting for anything?

[glebius]

I'm not sure the fix is 100% bulletproof. Neither flag not the parent pointer are assigned atomically.