Three more md fixes for 4.1

The main issue fixed here is a rare race which can result in two reshape
 threads running at once, which doesn't end well.
 Also a minor issue with a write to a sysfs file returning the wrong value.
 Backports to 4.0-stable are indicated.
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Merge tag 'md/4.1-rc7-fixes' of git://neil.brown.name/md

Pull three more md fixes from Neil Brown:
 "Hasn't been a good cycle for md has it :-(

  The main issue fixed here is a rare race which can result in two
  reshape threads running at once, which doesn't end well.

  Also a minor issue with a write to a sysfs file returning the wrong
  value.  Backports to 4.0-stable are indicated"

* tag 'md/4.1-rc7-fixes' of git://neil.brown.name/md:
  md: make sure MD_RECOVERY_DONE is clear before starting recovery/resync
  md: Close race when setting 'action' to 'idle'.
  md: don't return 0 from array_state_store

drivers/md/md.c

@@ -3834,7 +3834,7 @@ array_state_store(struct mddev *mddev, const char *buf, size_t len)
 				err = -EBUSY;
 		}
 		spin_unlock(&mddev->lock);
-		return err;
+		return err ?: len;
 	}
 	err = mddev_lock(mddev);
 	if (err)
@@ -4217,13 +4217,14 @@ action_store(struct mddev *mddev, const char *page, size_t len)
 			set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
 		else
 			clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
-		flush_workqueue(md_misc_wq);
-		if (mddev->sync_thread) {
-			set_bit(MD_RECOVERY_INTR, &mddev->recovery);
-			if (mddev_lock(mddev) == 0) {
+		if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) &&
+		    mddev_lock(mddev) == 0) {
+			flush_workqueue(md_misc_wq);
+			if (mddev->sync_thread) {
+				set_bit(MD_RECOVERY_INTR, &mddev->recovery);
 				md_reap_sync_thread(mddev);
-				mddev_unlock(mddev);
 			}
+			mddev_unlock(mddev);
 		}
 	} else if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||
 		   test_bit(MD_RECOVERY_NEEDED, &mddev->recovery))
@@ -8261,6 +8262,7 @@ void md_reap_sync_thread(struct mddev *mddev)
 	if (mddev_is_clustered(mddev))
 		md_cluster_ops->metadata_update_finish(mddev);
 	clear_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
+	clear_bit(MD_RECOVERY_DONE, &mddev->recovery);
 	clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
 	clear_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
 	clear_bit(MD_RECOVERY_REQUESTED, &mddev->recovery);

drivers/md/raid10.c

@@ -4156,6 +4156,7 @@ static int raid10_start_reshape(struct mddev *mddev)
 
 	clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
 	clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
+	clear_bit(MD_RECOVERY_DONE, &mddev->recovery);
 	set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
 	set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
 

drivers/md/raid5.c

@@ -7354,6 +7354,7 @@ static int raid5_start_reshape(struct mddev *mddev)
 
 	clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
 	clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
+	clear_bit(MD_RECOVERY_DONE, &mddev->recovery);
 	set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
 	set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
 	mddev->sync_thread = md_register_thread(md_do_sync, mddev,