reworking of inpcbinfo locking:
(1) Convert inpcb reference counting from manually manipulated integers to
the refcount(9) KPI. This allows the refcount to be managed atomically
with an inpcb read lock rather than write lock, or even with no inpcb
lock at all. As a result, in_pcbref() also no longer requires an inpcb
lock, so can be performed solely using the lock used to look up an
inpcb.
(2) Shift more inpcb freeing activity from the in_pcbrele() context (via
in_pcbfree_internal) to the explicit in_pcbfree() context. This means
that the inpcb refcount is increasingly used only to maintain memory
stability, not actually defer the clean up of inpcb protocol parts.
This is desirable as many of those protocol parts required the pcbinfo
lock, which we'd like not to acquire in in_pcbrele() contexts. Document
this in comments better.
(3) Introduce new read-locked and write-locked in_pcbrele() variations,
in_pcbrele_rlocked() and in_pcbrele_wlocked(), which allow the inpcb to
be properly unlocked as needed. in_pcbrele() is a wrapper around the
latter, and should probably go away at some point. This makes it
easier to use this weak reference model when holding only a read lock,
as will happen in the future.
This may well be safe to MFC, but some more KBI analysis is required.
Reviewed by: bz
MFC after: 3 weeks
Sponsored by: Juniper Networks, Inc.
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