diff --git a/man/man5/zfs-module-parameters.5 b/man/man5/zfs-module-parameters.5
index 932342cfda21..bb54b77fcbbf 100644
--- a/man/man5/zfs-module-parameters.5
+++ b/man/man5/zfs-module-parameters.5
@@ -1049,6 +1049,26 @@ See the section "ZFS I/O SCHEDULER".
 Default value: \fB1\fR.
 .RE
 
+.sp
+.ne 2
+.na
+\fBzfs_vdev_parallel_open_enabled\fR (bool)
+.ad
+.RS 12n
+Accelerates vdev open from pool import or reopen from reload from cache by
+allow child vdevs to be opened in parallel.
+.sp
+This almost always deadlocks in unsupported stacked ZFS configurations where a
+zvol from one pool is the vdev for another pool via another type of block
+device. Some logic exists in the kernel module to disable this in the direct
+case when there is nothing in-between, but it is impossible to detect the
+indirect case where another block device exists inbetween. Disabling this will
+often make stacked ZFS configurations work, but they continue to be an
+unsupported configuration because it is subjected to regression testing.
+.sp
+Use \fB1\fR for yes (default) and \fB0\fR for no.
+.RE
+
 .sp
 .ne 2
 .na
diff --git a/module/zfs/vdev.c b/module/zfs/vdev.c
index 5ff5cf3b1271..16bf7aae066e 100644
--- a/module/zfs/vdev.c
+++ b/module/zfs/vdev.c
@@ -51,6 +51,11 @@
  */
 int metaslabs_per_vdev = 200;
 
+/*
+ * Allow system administrator to disable parallel open optimization so that
+ * unsupported ZFS on something else on zvol is semi-safe.
+ */
+int zfs_vdev_parallel_open_enabled = 1;
 /*
  * Virtual device management.
  */
@@ -1136,7 +1141,7 @@ vdev_uses_zvols(vdev_t *vd)
 	int c;
 
 #ifdef _KERNEL
-	if (zvol_is_zvol(vd->vdev_path))
+	if (zfs_vdev_parallel_open_enabled == 0 || zvol_is_zvol(vd->vdev_path))
 		return (B_TRUE);
 #endif
 
@@ -3642,6 +3647,10 @@ EXPORT_SYMBOL(vdev_online);
 EXPORT_SYMBOL(vdev_offline);
 EXPORT_SYMBOL(vdev_clear);
 
+module_param(zfs_vdev_parallel_open_enabled, int, 0644);
+MODULE_PARM_DESC(zfs_vdev_parallel_open_enabled,
+	"Open vdev children in parallel during import.");
+
 module_param(metaslabs_per_vdev, int, 0644);
 MODULE_PARM_DESC(metaslabs_per_vdev,
 	"Divide added vdev into approximately (but no more than) this number "