Panic on NetBSD-9 using zfs receive and xen

[Brian Buhrow <buhrow%nfbcal.org@localhost>]

	hello.  I'm experimenting with a NetBSD-9 Xen server running zfs
volumes as domU disks.  While runing a zfs receive of a snapshot of a domU
disk from another server, I experienced the following crash.  While this
could be zfs related, I've been running zfs receives numerous times on the
system without a problem.  This is on Dom0 with 8GB of RAm and 1 CPU.  This
is from NetBSD-9_BETA from about September 25, 2019.  I wasn't able to get
a crash dump, but, maybe, this log will help figure out what's going wrong.
It seems like a race condition in the pool code, but I'm not familiar with
that part of the kernel enough to provide a lot of detail at the moment.
	has anyone else seen this issue?  Is it a known problem or should I
file a bug?

-thanks
-Brian


[ 12156.8100589] panic: kernel diagnostic assertion "(pp->pr_nout > 0)" failed: file "/usr/local/netbsd/src-90/sys/kern/subr_pool.c", line 1146 pool_do_put: [xbbrp] putting with none out
[ 12156.8100589] cpu0: Begin traceback...
[ 12156.8100589] vpanic() at netbsd:vpanic+0x143
[ 12156.8100589] kern_assert() at netbsd:kern_assert+0x48
[ 12156.8100589] pool_put() at netbsd:pool_put+0x5b6
[ 12156.8100589] pool_cache_invalidate_groups() at netbsd:pool_cache_invalidate_groups+0x59
[ 12156.8100589] pool_reclaim() at netbsd:pool_reclaim+0x72
[ 12156.8100589] pool_drain() at netbsd:pool_drain+0x85
[ 12156.8200580] uvmpd_pool_drain_thread() at netbsd:uvmpd_pool_drain_thread+0x74
[ 12156.8200580] cpu0: End traceback...

[ 12156.8200580] dumping to dev 168,11 (offset=2097007, size=0): not possible
[ 12156.8200580] rebooting...