An #ifdef that Taylor added in the new DRM code was bugging me, because a
similar situation already existed in the NetBSD kernel, whereby the type
stability of a object’s backing memory (the iam existentium case being LWPs)
was required for a passively-serialized weak reference to work. The LWP pool
cache had a hack to handle it, and the hack was propagated to the new DRM code
under an “#ifdef __NetBSD__”.
I initially fixed this by adding a “pre-destruct” callback that could be
optionally set for a pool cache, but after further discussion, it seemed like
having direct knowledge of passive serialization synchronization points in the
allocator was a better solution, so here is a diff that implements it for you
review.
https://www.netbsd.org/~thorpej/pool-pser-diff.txt
Please comment ASAP, because I want to ride a kernel version bump.
-- thorpej
