K 10
svn:author
V 3
kib
K 8
svn:date
V 27
2017-06-30T16:16:21.277140Z
K 7
svn:log
V 498
Correct fences for sys/refcount.h.

The acq barrier in refcount_acquire() has no use, constructor must
ensure that the changes are visible before publication by other means.
Last release must sync/with the constructor and all updaters.

This is based on the refcount/shared_ptr analysis I heard at the Hans
Boehm and Herb Sutter talks about C++ atomics.

Reviewed by:	alc, jhb, markj
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
Differential revision:	https://reviews.freebsd.org/D11270

END