vnet: (read) lock the vnet list while iterating it

[kp]

Summary

Ensure that the vnet list cannot be modified while we're running through
it.

MFC after: 1 week
Sponsored by: Rubicon Communications, LLC ("Netgate")

[mjg]

sys/net/vnet.c

608

you should unlock in the same order for consistency

the VNET_FOREACH macro should presumably assert on the lock?

[kp]

sys/net/vnet.c

608

It should, but the locking for the vnet list uses two different locks for reasons I do not currently understand.
So we'd have to MPASS(sx_locked(&vnet_sxlock) || rw_rowned(&vnet_rwlock));. Which is doubly annoying because rw_rowned() doesn't exist.

[kp]

reorder unlock

[mjg]

sys/net/vnet.c

608

that is a gap i'm going to plug

[zlei]

sys/net/vnet.c

596

In vnet_register_sysinit() we have lock order

VNET_SYSINIT_WLOCK();
VNET_LIST_RLOCK;

I think it is best to make lock order consistent with that in vnet_register_sysinit(), although dead lock is not possible.

608

you should unlock in the same order for consistency

I'd prefer to unlock in the reverse order. That is more natural for me.
Anyway unlock order does not matter much.

the VNET_FOREACH macro should presumably assert on the lock?

ipreass_drain() in sys/netinet/ip_reass.c also miss read lock.
I think it is good to have read lock assert in macro VNET_FOREACH .