3 files changed, 53 insertions, 2 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index e6f899dc5e47..f4a439e1a43f 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -756,6 +756,12 @@ struct btrfs_dir_item {
 
 #define BTRFS_ROOT_SUBVOL_RDONLY	(1ULL << 0)
 
+/*
+ * Internal in-memory flag that a subvolume has been marked for deletion but
+ * still visible as a directory
+ */
+#define BTRFS_ROOT_SUBVOL_DEAD		(1ULL << 48)
+
 struct btrfs_root_item {
 	struct btrfs_inode_item inode;
 	__le64 generation;
@@ -2791,6 +2797,11 @@ static inline bool btrfs_root_readonly(struct btrfs_root *root)
 	return (root->root_item.flags & cpu_to_le64(BTRFS_ROOT_SUBVOL_RDONLY)) != 0;
 }
 
+static inline bool btrfs_root_dead(struct btrfs_root *root)
+{
+	return (root->root_item.flags & cpu_to_le64(BTRFS_ROOT_SUBVOL_DEAD)) != 0;
+}
+
 /* struct btrfs_root_backup */
 BTRFS_SETGET_STACK_FUNCS(backup_tree_root, struct btrfs_root_backup,
 		   tree_root, 64);
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 2db12fc3f748..2db3fe12f50d 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2219,6 +2219,7 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
 	struct btrfs_ioctl_vol_args *vol_args;
 	struct btrfs_trans_handle *trans;
 	struct btrfs_block_rsv block_rsv;
+	u64 root_flags;
 	u64 qgroup_reserved;
 	int namelen;
 	int ret;
@@ -2240,6 +2241,7 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
 	if (err)
 		goto out;
 
+
 	err = mutex_lock_killable_nested(&dir->i_mutex, I_MUTEX_PARENT);
 	if (err == -EINTR)
 		goto out_drop_write;
@@ -2301,6 +2303,27 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
 	}
 
 	mutex_lock(&inode->i_mutex);
+
+	/*
+	 * Don't allow to delete a subvolume with send in progress. This is
+	 * inside the i_mutex so the error handling that has to drop the bit
+	 * again is not run concurrently.
+	 */
+	spin_lock(&dest->root_item_lock);
+	root_flags = btrfs_root_flags(&root->root_item);
+	if (root->send_in_progress == 0) {
+		btrfs_set_root_flags(&root->root_item,
+				root_flags | BTRFS_ROOT_SUBVOL_DEAD);
+		spin_unlock(&dest->root_item_lock);
+	} else {
+		spin_unlock(&dest->root_item_lock);
+		btrfs_warn(root->fs_info,
+			"Attempt to delete subvolume %llu during send",
+			root->root_key.objectid);
+		err = -EPERM;
+		goto out_dput;
+	}
+
 	err = d_invalidate(dentry);
 	if (err)
 		goto out_unlock;
@@ -2389,6 +2412,13 @@ out_release:
 out_up_write:
 	up_write(&root->fs_info->subvol_sem);
 out_unlock:
+	if (err) {
+		spin_lock(&dest->root_item_lock);
+		root_flags = btrfs_root_flags(&root->root_item);
+		btrfs_set_root_flags(&root->root_item,
+				root_flags & ~BTRFS_ROOT_SUBVOL_DEAD);
+		spin_unlock(&dest->root_item_lock);
+	}
 	mutex_unlock(&inode->i_mutex);
 	if (!err) {
 		shrink_dcache_sb(root->fs_info->sb);
diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 484aacac2c89..c76400dda4df 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -5518,7 +5518,7 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_)
 
 	/*
 	 * The subvolume must remain read-only during send, protect against
-	 * making it RW.
+	 * making it RW. This also protects against deletion.
 	 */
 	spin_lock(&send_root->root_item_lock);
 	send_root->send_in_progress++;
@@ -5578,6 +5578,15 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_)
 	}
 
 	sctx->send_root = send_root;
+	/*
+	 * Unlikely but possible, if the subvolume is marked for deletion but
+	 * is slow to remove the directory entry, send can still be started
+	 */
+	if (btrfs_root_dead(sctx->send_root)) {
+		ret = -EPERM;
+		goto out;
+	}
+
 	sctx->clone_roots_cnt = arg->clone_sources_count;
 
 	sctx->send_max_size = BTRFS_SEND_BUF_SIZE;
@@ -5667,7 +5676,8 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_)
 
 		spin_lock(&sctx->parent_root->root_item_lock);
 		sctx->parent_root->send_in_progress++;
-		if (!btrfs_root_readonly(sctx->parent_root)) {
+		if (!btrfs_root_readonly(sctx->parent_root) ||
+				btrfs_root_dead(sctx->parent_root)) {
 			spin_unlock(&sctx->parent_root->root_item_lock);
 			srcu_read_unlock(&fs_info->subvol_srcu, index);
 			ret = -EPERM;