btrfs: hold a ref on the root in btrfs_ioctl_send

We lookup all the clone roots and the parent root for send, so we need
to hold refs on all of these roots while we're processing them.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/send.c

@@ -7201,10 +7201,16 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
 				ret = PTR_ERR(clone_root);
 				goto out;
 			}
+			if (!btrfs_grab_fs_root(clone_root)) {
+				srcu_read_unlock(&fs_info->subvol_srcu, index);
+				ret = -ENOENT;
+				goto out;
+			}
 			spin_lock(&clone_root->root_item_lock);
 			if (!btrfs_root_readonly(clone_root) ||
 			    btrfs_root_dead(clone_root)) {
 				spin_unlock(&clone_root->root_item_lock);
+				btrfs_put_fs_root(clone_root);
 				srcu_read_unlock(&fs_info->subvol_srcu, index);
 				ret = -EPERM;
 				goto out;
@@ -7212,6 +7218,7 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
 			if (clone_root->dedupe_in_progress) {
 				dedupe_in_progress_warn(clone_root);
 				spin_unlock(&clone_root->root_item_lock);
+				btrfs_put_fs_root(clone_root);
 				srcu_read_unlock(&fs_info->subvol_srcu, index);
 				ret = -EAGAIN;
 				goto out;
@@ -7240,6 +7247,12 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
 			ret = PTR_ERR(sctx->parent_root);
 			goto out;
 		}
+		if (!btrfs_grab_fs_root(sctx->parent_root)) {
+			srcu_read_unlock(&fs_info->subvol_srcu, index);
+			ret = -ENOENT;
+			sctx->parent_root = ERR_PTR(ret);
+			goto out;
+		}
 
 		spin_lock(&sctx->parent_root->root_item_lock);
 		sctx->parent_root->send_in_progress++;
@@ -7267,7 +7280,8 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
 	 * is behind the current send position. This is checked while searching
 	 * for possible clone sources.
 	 */
-	sctx->clone_roots[sctx->clone_roots_cnt++].root = sctx->send_root;
+	sctx->clone_roots[sctx->clone_roots_cnt++].root =
+		btrfs_grab_fs_root(sctx->send_root);
 
 	/* We do a bsearch later */
 	sort(sctx->clone_roots, sctx->clone_roots_cnt,
@@ -7352,18 +7366,24 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
 	}
 
 	if (sort_clone_roots) {
-		for (i = 0; i < sctx->clone_roots_cnt; i++)
+		for (i = 0; i < sctx->clone_roots_cnt; i++) {
 			btrfs_root_dec_send_in_progress(
 					sctx->clone_roots[i].root);
+			btrfs_put_fs_root(sctx->clone_roots[i].root);
+		}
 	} else {
-		for (i = 0; sctx && i < clone_sources_to_rollback; i++)
+		for (i = 0; sctx && i < clone_sources_to_rollback; i++) {
 			btrfs_root_dec_send_in_progress(
 					sctx->clone_roots[i].root);
+			btrfs_put_fs_root(sctx->clone_roots[i].root);
+		}
 
 		btrfs_root_dec_send_in_progress(send_root);
 	}
-	if (sctx && !IS_ERR_OR_NULL(sctx->parent_root))
+	if (sctx && !IS_ERR_OR_NULL(sctx->parent_root)) {
 		btrfs_root_dec_send_in_progress(sctx->parent_root);
+		btrfs_put_fs_root(sctx->parent_root);
+	}
 
 	kvfree(clone_sources_tmp);