[Bug 200319] Bridge+CARP crashes/freezes

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=200319

            Bug ID: 200319
           Summary: Bridge+CARP crashes/freezes
           Product: Base System
           Version: 10.1-RELEASE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Many People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: eri at pfsense.org

Created attachment 156928
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=156928&action=edit
Fixes on carp+bridge freeze

The interaction between carp and bridge code makes the OS hang.

If there is a bridge with member an interface that has a CARP ip and no minimal
amount of traffic flowing in the system result is a hang of the system and
sometimes a crash.

Reference https://redmine.pfsense.org/issues/4607

After analysis seems that the carp code uses taskqueue_swi for scheduling
demotion events.
The carp CIF lock had a lot of contention.
ether_input was doing duplicate checks of bridge_input causing even more
contention on the CIF lock.

Attached patch converts CIF lock to RW lock.
It avoids duplicate checks from ether_input in case of bridge
schedules the taskqueue as taskqueue_thread rather than a SWI thread.

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