Index: sys/kern/subr_pool.c
===================================================================
RCS file: /cvsroot/src/sys/kern/subr_pool.c,v
retrieving revision 1.210
diff -p -u -r1.210 subr_pool.c
--- sys/kern/subr_pool.c	5 Nov 2017 07:49:45 -0000	1.210
+++ sys/kern/subr_pool.c	6 Nov 2017 16:45:22 -0000
@@ -805,6 +805,7 @@ pool_get(struct pool *pp, int flags)
 		pp->pr_nfail++;
 
 		mutex_exit(&pp->pr_lock);
+		KASSERT((flags & (PR_WAITOK|PR_NOWAIT)) == PR_NOWAIT);
 		return (NULL);
 	}
 
@@ -848,6 +849,7 @@ pool_get(struct pool *pp, int flags)
 
 			pp->pr_nfail++;
 			mutex_exit(&pp->pr_lock);
+			KASSERT((flags & (PR_WAITOK|PR_NOWAIT)) == PR_NOWAIT);
 			return (NULL);
 		}
 
@@ -2181,8 +2183,10 @@ pool_cache_get_slow(pool_cache_cpu_t *cc
 
 	object = pool_get(&pc->pc_pool, flags);
 	*objectp = object;
-	if (__predict_false(object == NULL))
+	if (__predict_false(object == NULL)) {
+		KASSERT((flags & (PR_WAITOK|PR_NOWAIT)) == PR_NOWAIT);
 		return false;
+	}
 
 	if (__predict_false((*pc->pc_ctor)(pc->pc_arg, object, flags) != 0)) {
 		pool_put(&pc->pc_pool, object);
@@ -2273,6 +2277,11 @@ pool_cache_get_paddr(pool_cache_t pc, in
 			break;
 	}
 
+	/*
+	 * We would like to KASSERT(object || (flags & PR_NOWAIT)), but
+	 * pool_cache_get can fail even in the PR_WAITOK case, if the
+	 * constructor fails.
+	 */
 	return object;
 }