K 10
svn:author
V 6
obrien
K 8
svn:date
V 27
2022-02-22T07:30:53.164403Z
K 7
svn:log
V 950
random(4): Make entropy source deregistration safe

Allow loadable modules that provide random entropy source(s) to safely
unload.  Prior to this change, no driver could ensure that their
random_source structure was not being used by random_harvestq.c for any
period of time after invoking random_source_deregister().

This change converts the source_list LIST to a ConcurrencyKit CK_LIST and
uses an epoch(9) to protect typical read accesses of the list.  The existing
HARVEST_LOCK spin mutex is used to safely add and remove list entries.
random_source_deregister() uses epoch_wait() to ensure no concurrent
source_list readers are accessing a random_source before freeing the list
item and returning to the caller.

Callers can safely unload immediately after random_source_deregister()
returns.

(cherry picked from commit 374c99911ee45c5d2ddd42bc6bcf711a8a66b07e)

Git Hash:   7878a69e0415251e4c7a0d3447f998207258ad41
Git Author: cem@FreeBSD.org
END