btrfs: return error if we're unable to read device stats

I noticed when fixing device stats for seed devices that we simply threw
away the return value from btrfs_search_slot().  This is because we may
not have stat items, but we could very well get an error, and thus miss
reporting the error up the chain.

Fix this by returning ret if it's an actual error, and then stop trying
to init the rest of the devices stats and return the error up the chain.

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -7223,8 +7223,8 @@ static void btrfs_set_dev_stats_value(struct extent_buffer *eb,
 			    sizeof(val));
 }
 
-static void btrfs_device_init_dev_stats(struct btrfs_device *device,
-					struct btrfs_path *path)
+static int btrfs_device_init_dev_stats(struct btrfs_device *device,
+				       struct btrfs_path *path)
 {
 	struct btrfs_dev_stats_item *ptr;
 	struct extent_buffer *eb;
@@ -7241,7 +7241,7 @@ static void btrfs_device_init_dev_stats(struct btrfs_device *device,
 			btrfs_dev_stat_set(device, i, 0);
 		device->dev_stats_valid = 1;
 		btrfs_release_path(path);
-		return;
+		return ret < 0 ? ret : 0;
 	}
 	slot = path->slots[0];
 	eb = path->nodes[0];
@@ -7260,29 +7260,39 @@ static void btrfs_device_init_dev_stats(struct btrfs_device *device,
 	device->dev_stats_valid = 1;
 	btrfs_dev_stat_print_on_load(device);
 	btrfs_release_path(path);
+
+	return 0;
 }
 
 int btrfs_init_dev_stats(struct btrfs_fs_info *fs_info)
 {
 	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices, *seed_devs;
 	struct btrfs_device *device;
 	struct btrfs_path *path = NULL;
+	int ret = 0;
 
 	path = btrfs_alloc_path();
 	if (!path)
 		return -ENOMEM;
 
 	mutex_lock(&fs_devices->device_list_mutex);
-	list_for_each_entry(device, &fs_devices->devices, dev_list)
-		btrfs_device_init_dev_stats(device, path);
+	list_for_each_entry(device, &fs_devices->devices, dev_list) {
+		ret = btrfs_device_init_dev_stats(device, path);
+		if (ret)
+			goto out;
+	}
 	list_for_each_entry(seed_devs, &fs_devices->seed_list, seed_list) {
-		list_for_each_entry(device, &seed_devs->devices, dev_list)
-			btrfs_device_init_dev_stats(device, path);
+		list_for_each_entry(device, &seed_devs->devices, dev_list) {
+			ret = btrfs_device_init_dev_stats(device, path);
+			if (ret)
+				goto out;
+		}
 	}
+out:
 	mutex_unlock(&fs_devices->device_list_mutex);
 
 	btrfs_free_path(path);
-	return 0;
+	return ret;
 }
 
 static int update_dev_stat_item(struct btrfs_trans_handle *trans,