Wait for resilver after online

This test performs a rapid offline/online cycle of each of several
mirror vdevs.  It can run so quickly that there isn't sufficient pool
redundancy to perform an offline.  The solution is to wait until the
pool is resilvered following the online operation.

Also, add a pool sync before the offline operation to help reduce
spurious errors.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Tim Chase <[email protected]>
Issue openzfs#6900

tests/zfs-tests/tests/functional/cli_root/zpool_online/zpool_online_001_pos.ksh

@@ -71,10 +71,13 @@ if [[ -z $DISKLIST ]]; then
 fi
 
 typeset -i i=0
+typeset -i j=0
 
 for disk in $DISKLIST; do
 	i=0
 	while [[ $i -lt ${#args[*]} ]]; do
+
+		log_must sync_pool $TESTPOOL
 		log_must zpool offline $TESTPOOL $disk
 		check_state $TESTPOOL $disk "offline"
 		if [[ $? != 0 ]]; then
@@ -87,6 +90,14 @@ for disk in $DISKLIST; do
 			log_fail "$disk of $TESTPOOL did not match online state"
 		fi
 
+		while [[ $j -lt 20 ]]; do
+			is_pool_resilvered $TESTPOOL && break
+			sleep 0.5
+			(( j = j + 1 ))
+		done
+		is_pool_resilvered $TESTPOOL || \
+		    log_file "Pool didn't resilver after online"
+
 		(( i = i + 1 ))
 	done
 done