Fix a race in the SMP rendezvous code. Specifically, the write by the

last CPU to to finish the rendezvous action may become visible to
different CPUs at different times.  As a result, the CPU that initiated
the rendezvous may exit the rendezvous and drop the lock allowing another
rendezvous to be initiated on the same CPU or a different CPU.  In that
case the exit sentinel may be cleared before all CPUs have noticed causing
those CPUs to hang forever.

Workaround this by using a generation count to notice when this race
occurs and to exit the rendezvous in that case.

The problem was independently diagnosted by mlaier@ and avg@ as well.

Submitted by:	neel
Reviewed by:	avg, mlaier
Obtained from:	NetApp
MFC after:	1 week

0 files changed, 0 insertions, 0 deletions