diff --git a/lib/libzfs/libzfs_mount.c b/lib/libzfs/libzfs_mount.c
index 649c232aa3e5..d62801cfdaca 100644
--- a/lib/libzfs/libzfs_mount.c
+++ b/lib/libzfs/libzfs_mount.c
@@ -1302,12 +1302,14 @@ mountpoint_cmp(const void *arga, const void *argb)
 }
 
 /*
- * Return true if path2 is a child of path1.
+ * Return true if path2 is a child of path1 or path2 equals path1 or
+ * path1 is "/" (path2 is always a child of "/").
  */
 static boolean_t
 libzfs_path_contains(const char *path1, const char *path2)
 {
-	return (strstr(path2, path1) == path2 && path2[strlen(path1)] == '/');
+	return (strcmp(path1, path2) == 0 || strcmp(path1, "/") == 0 ||
+	    (strstr(path2, path1) == path2 && path2[strlen(path1)] == '/'));
 }
 
 /*
diff --git a/tests/runfiles/linux.run b/tests/runfiles/linux.run
index 1e2a719b2d0a..9d133632102e 100644
--- a/tests/runfiles/linux.run
+++ b/tests/runfiles/linux.run
@@ -182,7 +182,8 @@ tests = ['zfs_mount_001_pos', 'zfs_mount_002_pos', 'zfs_mount_003_pos',
     'zfs_mount_007_pos', 'zfs_mount_008_pos', 'zfs_mount_009_neg',
     'zfs_mount_010_neg', 'zfs_mount_011_neg', 'zfs_mount_012_neg',
     'zfs_mount_all_001_pos', 'zfs_mount_encrypted', 'zfs_mount_remount',
-    'zfs_multi_mount', 'zfs_mount_all_fail', 'zfs_mount_all_mountpoints']
+    'zfs_multi_mount', 'zfs_mount_all_fail', 'zfs_mount_all_mountpoints',
+    'zfs_mount_test_race']
 tags = ['functional', 'cli_root', 'zfs_mount']
 
 [tests/functional/cli_root/zfs_program]
diff --git a/tests/zfs-tests/tests/functional/cli_root/zfs_mount/Makefile.am b/tests/zfs-tests/tests/functional/cli_root/zfs_mount/Makefile.am
index b2de98934b74..c208a1c378dc 100644
--- a/tests/zfs-tests/tests/functional/cli_root/zfs_mount/Makefile.am
+++ b/tests/zfs-tests/tests/functional/cli_root/zfs_mount/Makefile.am
@@ -19,6 +19,7 @@ dist_pkgdata_SCRIPTS = \
 	zfs_mount_all_mountpoints.ksh \
 	zfs_mount_encrypted.ksh \
 	zfs_mount_remount.ksh \
+	zfs_mount_test_race.sh \
 	zfs_multi_mount.ksh
 
 dist_pkgdata_DATA = \
diff --git a/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_test_race.sh b/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_test_race.sh
new file mode 100755
index 000000000000..404770b2727f
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/cli_root/zfs_mount/zfs_mount_test_race.sh
@@ -0,0 +1,116 @@
+#!/bin/ksh
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2019 by Tomohiro Kusumi. All rights reserved.
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/cli_root/zfs_mount/zfs_mount.cfg
+
+#
+# DESCRIPTION:
+# Verify parallel mount ordering is consistent.
+#
+# There was a bug in initial thread dispatching algorithm which put threads
+# under race condition which resulted in undefined mount order.  The purpose
+# of this test is to verify `zfs unmount -a` succeeds (not `zfs mount -a`
+# succeeds, it always does) after `zfs mount -a`, which could fail if threads
+# race.  See github.com/zfsonlinux/zfs/issues/{8450,8833,8878} for details.
+#
+# STRATEGY:
+# 1. Create pools and filesystems.
+# 2. Set same mount point for >1 datasets.
+# 3. Unmount all datasets.
+# 4. Mount all datasets.
+# 5. Unmount all datasets (verify this succeeds).
+#
+
+verify_runnable "both"
+
+TMPDIR=${TMPDIR:-$TEST_BASE_DIR}
+MNTPT=$TMPDIR/zfs_mount_test_race_mntpt
+DISK1="$TMPDIR/zfs_mount_test_race_disk1"
+DISK2="$TMPDIR/zfs_mount_test_race_disk2"
+
+TESTPOOL1=zfs_mount_test_race_tp1
+TESTPOOL2=zfs_mount_test_race_tp2
+
+export __ZFS_POOL_RESTRICT="$TESTPOOL1 $TESTPOOL2"
+log_must zfs $unmountall
+unset __ZFS_POOL_RESTRICT
+
+function cleanup
+{
+	zpool destroy $TESTPOOL1
+	zpool destroy $TESTPOOL2
+	rm -rf $MNTPT
+	rm -rf /$TESTPOOL1
+	rm -rf /$TESTPOOL2
+	rm -f $DISK1
+	rm -f $DISK2
+	export __ZFS_POOL_RESTRICT="$TESTPOOL1 $TESTPOOL2"
+	log_must zfs $mountall
+	unset __ZFS_POOL_RESTRICT
+}
+log_onexit cleanup
+
+log_note "Verify parallel mount ordering is consistent"
+
+log_must truncate -s $MINVDEVSIZE $DISK1
+log_must truncate -s $MINVDEVSIZE $DISK2
+
+log_must zpool create -f $TESTPOOL1 $DISK1
+log_must zpool create -f $TESTPOOL2 $DISK2
+
+log_must zfs create $TESTPOOL1/$TESTFS1
+log_must zfs create $TESTPOOL2/$TESTFS2
+
+log_must zfs set mountpoint=none $TESTPOOL1
+log_must zfs set mountpoint=$MNTPT $TESTPOOL1/$TESTFS1
+
+# Note that unmount can fail (due to race condition on `zfs mount -a`) with or
+# without `canmount=off`.  The race has nothing to do with canmount property,
+# but turn it off for convenience of mount layout used in this test case.
+log_must zfs set canmount=off $TESTPOOL2
+log_must zfs set mountpoint=$MNTPT $TESTPOOL2
+
+# At this point, layout of datasets in two pools will look like below.
+# Previously, on next `zfs mount -a`, pthreads assigned to TESTFS1 and TESTFS2
+# could race, and TESTFS2 usually (actually always) won in ZoL.  Note that the
+# problem is how two or more threads could initially be assigned to the same
+# top level directory, not this specific layout.  This layout is just an example
+# that can reproduce race, and is also the layout reported in #8833.
+#
+# NAME                  MOUNTED  MOUNTPOINT
+# ----------------------------------------------
+# /$TESTPOOL1           no       none
+# /$TESTPOOL1/$TESTFS1  yes      $MNTPT
+# /$TESTPOOL2           no       $MNTPT
+# /$TESTPOOL2/$TESTFS2  yes      $MNTPT/$TESTFS2
+
+# Apparently two datasets must be mounted.
+log_must ismounted $TESTPOOL1/$TESTFS1
+log_must ismounted $TESTPOOL2/$TESTFS2
+# This unmount always succeeds, because potential race hasn't happened yet.
+log_must zfs unmount -a
+# This mount always succeeds, whether threads are under race condition or not.
+log_must zfs mount -a
+
+# Verify datasets are mounted (TESTFS2 fails if the race broke mount order).
+log_must ismounted $TESTPOOL1/$TESTFS1
+log_must ismounted $TESTPOOL2/$TESTFS2
+# Verify unmount succeeds (fails if the race broke mount order).
+log_must zfs unmount -a
+
+log_pass "Verify parallel mount ordering is consistent passed"