Index: sys/kern/subr_pool.c
===================================================================
RCS file: /cvsroot/src/sys/kern/subr_pool.c,v
retrieving revision 1.218
diff -p -u -r1.218 subr_pool.c
--- sys/kern/subr_pool.c	4 Dec 2017 03:05:24 -0000	1.218
+++ sys/kern/subr_pool.c	5 Dec 2017 19:54:03 -0000
@@ -1073,10 +1073,22 @@ pool_grow(struct pool *pp, int flags)
 			} while (pp->pr_flags & PR_GROWING);
 			return ERESTART;
 		} else {
+			if (pp->pr_flags & PR_GROWINGNOWAIT) {
+				/*
+				 * This needs an unlock/relock dance so
+				 * that the other caller has a chance to
+				 * run and actually do the thing.
+				 */
+				mutex_exit(&pp->pr_lock);
+				mutex_enter(&pp->pr_lock);
+				return ERESTART;
+			}
 			return EWOULDBLOCK;
 		}
 	}
 	pp->pr_flags |= PR_GROWING;
+	if ((flags & PR_WAITOK) == 0)
+		pp->pr_flags |= PR_GROWINGNOWAIT;
 
 	mutex_exit(&pp->pr_lock);
 	char *cp = pool_allocator_alloc(pp, flags);
@@ -1093,7 +1105,7 @@ pool_grow(struct pool *pp, int flags)
 	pool_prime_page(pp, cp, ph);
 	pp->pr_npagealloc++;
 	KASSERT(pp->pr_flags & PR_GROWING);
-	pp->pr_flags &= ~PR_GROWING;
+	pp->pr_flags &= ~(PR_GROWING|PR_GROWINGNOWAIT);
 	/*
 	 * If anyone was waiting for pool_grow, notify them that we
 	 * may have just done it.
@@ -1102,7 +1114,7 @@ pool_grow(struct pool *pp, int flags)
 	return 0;
 out:
 	KASSERT(pp->pr_flags & PR_GROWING);
-	pp->pr_flags &= ~PR_GROWING;
+	pp->pr_flags &= ~(PR_GROWING|PR_GROWINGNOWAIT);
 	mutex_enter(&pp->pr_lock);
 	return ENOMEM;
 }
Index: sys/sys/pool.h
===================================================================
RCS file: /cvsroot/src/sys/sys/pool.h,v
retrieving revision 1.81
diff -p -u -r1.81 pool.h
--- sys/sys/pool.h	2 Dec 2017 08:15:43 -0000	1.81
+++ sys/sys/pool.h	5 Dec 2017 19:54:03 -0000
@@ -148,6 +148,7 @@ struct pool {
 #define PR_NOALIGN	0x800	/* don't assume backend alignment */
 #define	PR_LARGECACHE	0x1000	/* use large cache groups */
 #define	PR_GROWING	0x2000	/* pool_grow in progress */
+#define	PR_GROWINGNOWAIT 0x4000	/* pool_grow in progress by PR_NOWAIT alloc */
 
 	/*
 	 * `pr_lock' protects the pool's data structures when removing