Fixes for spurious failures of resilver_restart_001 test

The resilver restart test was reported as failing about 2% of the
time. Two issues were found:
- The event log wasn't large enough, so resilver events were missing
- One 'zpool sync' wasn't enough for resilver to start after zinject

Signed-off-by: John Poduska <jpoduska@datto.com>
Closes #9677

tests/zfs-tests/tests/functional/resilver/resilver_restart_001.ksh

@@ -47,12 +47,13 @@ function cleanup
 {
 	echo $ORIG_RESILVER_MIN_TIME > $ZFS_PARAMS/zfs_resilver_min_time_ms
 	echo $ORIG_SCAN_SUSPEND_PROGRESS > $ZFS_PARAMS/zfs_scan_suspend_progress
+	echo $ORIG_ZFS_ZEVENT_LEN_MAX > $ZFS_PARAMS/zfs_zevent_len_max
 	log_must zinject -c all
 	destroy_pool $TESTPOOL
 	rm -f ${VDEV_FILES[@]} $SPARE_VDEV_FILE
 }
 
-# Count resilver events in zpool and number of deferred rsilvers on vdevs
+# count resilver events in zpool and number of deferred rsilvers on vdevs
 function verify_restarts # <msg> <cnt> <defer>
 {
 	msg=$1
@@ -88,6 +89,7 @@ log_assert "Check for unnecessary resilver restarts"
 ZFS_PARAMS=/sys/module/zfs/parameters
 ORIG_RESILVER_MIN_TIME=$(cat $ZFS_PARAMS/zfs_resilver_min_time_ms)
 ORIG_SCAN_SUSPEND_PROGRESS=$(cat $ZFS_PARAMS/zfs_scan_suspend_progress)
+ORIG_ZFS_ZEVENT_LEN_MAX=$(cat $ZFS_PARAMS/zfs_zevent_len_max)
 
 set -A RESTARTS -- '1' '2' '2' '2'
 set -A VDEVS -- '' '' '' ''
@@ -98,12 +100,15 @@ VDEV_REPLACE="${VDEV_FILES[1]} $SPARE_VDEV_FILE"
 
 log_onexit cleanup
 
+# ensure that enough events will be saved
+echo 512 > $ZFS_PARAMS/zfs_zevent_len_max
+
 log_must truncate -s $VDEV_FILE_SIZE ${VDEV_FILES[@]} $SPARE_VDEV_FILE
 
 log_must zpool create -f -o feature@resilver_defer=disabled $TESTPOOL \
     raidz ${VDEV_FILES[@]}
 
-# Create 4 filesystems
+# create 4 filesystems
 for fs in fs{0..3}
 do
 	log_must zfs create -o primarycache=none -o recordsize=1k $TESTPOOL/$fs
@@ -118,7 +123,7 @@ do
 done
 wait
 
-# Test without and with deferred resilve feature enabled
+# test without and with deferred resilve feature enabled
 for test in "without" "with"
 do
 	log_note "Testing $test deferred resilvers"
@@ -177,6 +182,7 @@ do
 
 	# wait for a few txg's to see if a resilver happens
 	log_must zpool sync $TESTPOOL
+	log_must zpool sync $TESTPOOL
 
 	# there should now be 2 resilver starts
 	verify_restarts ' after resilver' "${RESTARTS[3]}" "${VDEVS[3]}"