md: level_store: group all important changes into one place.

Gather all the changes that can happen atomically and might
be relevant to other code into one place.  This will
make it easier to refine the locking.

Note that this puts quite a few things between mddev_detach()
and ->free().  Enabling this was the point of some recent patches.

Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/md.c

@@ -3280,9 +3280,9 @@ level_store(struct mddev *mddev, const char *buf, size_t len)
 {
 	char clevel[16];
 	ssize_t rv = len;
-	struct md_personality *pers;
+	struct md_personality *pers, *oldpers;
 	long level;
-	void *priv;
+	void *priv, *oldpriv;
 	struct md_rdev *rdev;
 
 	if (mddev->pers == NULL) {
@@ -3374,25 +3374,19 @@ level_store(struct mddev *mddev, const char *buf, size_t len)
 	/* Looks like we have a winner */
 	mddev_suspend(mddev);
 	mddev_detach(mddev);
-	mddev->pers->free(mddev, mddev->private);
+	oldpers = mddev->pers;
+	oldpriv = mddev->private;
+	mddev->pers = pers;
+	mddev->private = priv;
+	strlcpy(mddev->clevel, pers->name, sizeof(mddev->clevel));
+	mddev->level = mddev->new_level;
+	mddev->layout = mddev->new_layout;
+	mddev->chunk_sectors = mddev->new_chunk_sectors;
+	mddev->delta_disks = 0;
+	mddev->reshape_backwards = 0;
+	mddev->degraded = 0;
 
-	if (mddev->pers->sync_request == NULL &&
-	    pers->sync_request != NULL) {
-		/* need to add the md_redundancy_group */
-		if (sysfs_create_group(&mddev->kobj, &md_redundancy_group))
-			printk(KERN_WARNING
-			       "md: cannot register extra attributes for %s\n",
-			       mdname(mddev));
-		mddev->sysfs_action = sysfs_get_dirent(mddev->kobj.sd, "sync_action");
-	}
-	if (mddev->pers->sync_request != NULL &&
-	    pers->sync_request == NULL) {
-		/* need to remove the md_redundancy_group */
-		if (mddev->to_remove == NULL)
-			mddev->to_remove = &md_redundancy_group;
-	}
-
-	if (mddev->pers->sync_request == NULL &&
+	if (oldpers->sync_request == NULL &&
 	    mddev->external) {
 		/* We are converting from a no-redundancy array
 		 * to a redundancy array and metadata is managed
@@ -3406,6 +3400,24 @@ level_store(struct mddev *mddev, const char *buf, size_t len)
 		mddev->safemode = 0;
 	}
 
+	oldpers->free(mddev, oldpriv);
+
+	if (oldpers->sync_request == NULL &&
+	    pers->sync_request != NULL) {
+		/* need to add the md_redundancy_group */
+		if (sysfs_create_group(&mddev->kobj, &md_redundancy_group))
+			printk(KERN_WARNING
+			       "md: cannot register extra attributes for %s\n",
+			       mdname(mddev));
+		mddev->sysfs_action = sysfs_get_dirent(mddev->kobj.sd, "sync_action");
+	}
+	if (oldpers->sync_request != NULL &&
+	    pers->sync_request == NULL) {
+		/* need to remove the md_redundancy_group */
+		if (mddev->to_remove == NULL)
+			mddev->to_remove = &md_redundancy_group;
+	}
+
 	rdev_for_each(rdev, mddev) {
 		if (rdev->raid_disk < 0)
 			continue;
@@ -3431,17 +3443,7 @@ level_store(struct mddev *mddev, const char *buf, size_t len)
 		}
 	}
 
-	module_put(mddev->pers->owner);
-	mddev->pers = pers;
-	mddev->private = priv;
-	strlcpy(mddev->clevel, pers->name, sizeof(mddev->clevel));
-	mddev->level = mddev->new_level;
-	mddev->layout = mddev->new_layout;
-	mddev->chunk_sectors = mddev->new_chunk_sectors;
-	mddev->delta_disks = 0;
-	mddev->reshape_backwards = 0;
-	mddev->degraded = 0;
-	if (mddev->pers->sync_request == NULL) {
+	if (pers->sync_request == NULL) {
 		/* this is now an array without redundancy, so
 		 * it must always be in_sync
 		 */