md: 'sync_action' in sysfs returns wrong value for readonly arrays

When an array is started read-only, MD_RECOVERY_NEEDED can be set but no
recovery will be running.  This causes 'sync_action' to report the wrong
value.

We could remove the test for MD_RECOVERY_NEEDED, but doing so would leave a
small gap after requesting a sync action, where 'sync_action' would still
report the old value.

So make sure that for a read-only array, 'sync_action' always returns 'idle'.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/md/md.c

@@ -2714,7 +2714,7 @@ action_show(mddev_t *mddev, char *page)
 {
 	char *type = "idle";
 	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||
-	    test_bit(MD_RECOVERY_NEEDED, &mddev->recovery)) {
+	    (!mddev->ro && test_bit(MD_RECOVERY_NEEDED, &mddev->recovery))) {
 		if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
 			type = "reshape";
 		else if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {