The previous code took locks the following order:
- LLE_WLOCKs
- mutex_enter(softnet_lock)
- LLE_WUNLOCKs
- mutex_exit(softnet_lock)
This fix moves mutex_enter(softnet_lock) before LLE_WLOCKs.
We have to touch la_rt always with holding softnet_lock. And we have to
use callout_halt with softnet_lock instead of callout_stop for
la_timer (arptimer) because arptimer holds softnet_lock inside it.
This fix may solve a kernel panic christos@ encountered.
Highlights of the change are:
- Use llentry instead of llinfo to manage ARP caches
- ARP specific data are stored in the hashed list
of an interface instead of the global list (llinfo_arp)
- Fine-grain locking on llentry
- arptimer (callout) per ARP cache
- the global timer callout with the big locks can be
removed (though softnet_lock is still required for now)
- net.inet.arp.prune is now obsoleted
- it was the interval of the global timer callout
- net.inet.arp.refresh is now obsoleted
- it was a parameter that prevents expiration of active caches
- Removed to simplify the timer logic, but we may be able to
restore the feature if really needed
Proposed on tech-kern and tech-net.
lltable/llentry is new L2 nexthop cache data structures that
store caches in each interface (struct ifnet). It is imported
to replace the current ARP cache implementation that uses the
global list with the big kernel lock, and provide fine-grain
locking for cache operations. It is also planned to replace
NDP caches.
The code is based on FreeBSD's lltable/llentry as of r286629
and tweaked for NetBSD.
ozaki-r