Btrfs: fix send attempting to rmdir non-empty directories

The incremental send algorithm assumed that it was possible to issue
a directory remove (rmdir) if the the inode number it was currently
processing was greater than (or equal) to any inode that referenced
the directory's inode. This wasn't a valid assumption because any such
inode might be a child directory that is pending a move/rename operation,
because it was moved into a directory that has a higher inode number and
was moved/renamed too - in other words, the case the following commit
addressed:

    9f03740a
    (Btrfs: fix infinite path build loops in incremental send)

This made an incremental send issue an rmdir operation before the
target directory was actually empty, which made btrfs receive fail.
Therefore it needs to wait for all pending child directory inodes to
be moved/renamed before sending an rmdir operation.

Simple steps to reproduce this issue:

    $ mkfs.btrfs -f /dev/sdb3
    $ mount /dev/sdb3 /mnt/btrfs
    $ mkdir -p /mnt/btrfs/a/b/c/x
    $ mkdir /mnt/btrfs/a/b/y
    $ btrfs subvolume snapshot -r /mnt/btrfs /mnt/btrfs/snap1
    $ btrfs send /mnt/btrfs/snap1 -f /tmp/base.send
    $ mv /mnt/btrfs/a/b/y /mnt/btrfs/a/b/YY
    $ mv /mnt/btrfs/a/b/c/x /mnt/btrfs/a/b/YY
    $ rmdir /mnt/btrfs/a/b/c
    $ btrfs subvolume snapshot -r /mnt/btrfs /mnt/btrfs/snap2
    $ btrfs send -p /mnt/btrfs/snap1 /mnt/btrfs/snap2 -f /tmp/incremental.send

    $ umount /mnt/btrfs
    $ mkfs.btrfs -f /dev/sdb3
    $ mount /dev/sdb3 /mnt/btrfs
    $ btrfs receive /mnt/btrfs -f /tmp/base.send
    $ btrfs receive /mnt/btrfs -f /tmp/incremental.send

The second btrfs receive command failed with:

    ERROR: rmdir o259-6-0 failed. Directory not empty

A test case for xfstests follows.
Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>

fs/btrfs/send.c

@@ -178,6 +178,47 @@ struct send_ctx {
 	 * own move/rename can be performed.
 	 */
 	struct rb_root waiting_dir_moves;
+
+	/*
+	 * A directory that is going to be rm'ed might have a child directory
+	 * which is in the pending directory moves index above. In this case,
+	 * the directory can only be removed after the move/rename of its child
+	 * is performed. Example:
+	 *
+	 * Parent snapshot:
+	 *
+	 * .                        (ino 256)
+	 * |-- a/                   (ino 257)
+	 *     |-- b/               (ino 258)
+	 *         |-- c/           (ino 259)
+	 *         |   |-- x/       (ino 260)
+	 *         |
+	 *         |-- y/           (ino 261)
+	 *
+	 * Send snapshot:
+	 *
+	 * .                        (ino 256)
+	 * |-- a/                   (ino 257)
+	 *     |-- b/               (ino 258)
+	 *         |-- YY/          (ino 261)
+	 *              |-- x/      (ino 260)
+	 *
+	 * Sequence of steps that lead to the send snapshot:
+	 * rm -f /a/b/c/foo.txt
+	 * mv /a/b/y /a/b/YY
+	 * mv /a/b/c/x /a/b/YY
+	 * rmdir /a/b/c
+	 *
+	 * When the child is processed, its move/rename is delayed until its
+	 * parent is processed (as explained above), but all other operations
+	 * like update utimes, chown, chgrp, etc, are performed and the paths
+	 * that it uses for those operations must use the orphanized name of
+	 * its parent (the directory we're going to rm later), so we need to
+	 * memorize that name.
+	 *
+	 * Indexed by the inode number of the directory to be deleted.
+	 */
+	struct rb_root orphan_dirs;
 };
 
 struct pending_dir_move {
@@ -192,6 +233,18 @@ struct pending_dir_move {
 struct waiting_dir_move {
 	struct rb_node node;
 	u64 ino;
+	/*
+	 * There might be some directory that could not be removed because it
+	 * was waiting for this directory inode to be moved first. Therefore
+	 * after this directory is moved, we can try to rmdir the ino rmdir_ino.
+	 */
+	u64 rmdir_ino;
+};
+
+struct orphan_dir_info {
+	struct rb_node node;
+	u64 ino;
+	u64 gen;
 };
 
 struct name_cache_entry {
@@ -217,6 +270,11 @@ struct name_cache_entry {
 
 static int is_waiting_for_move(struct send_ctx *sctx, u64 ino);
 
+static struct waiting_dir_move *
+get_waiting_dir_move(struct send_ctx *sctx, u64 ino);
+
+static int is_waiting_for_rm(struct send_ctx *sctx, u64 dir_ino);
+
 static int need_send_hole(struct send_ctx *sctx)
 {
 	return (sctx->parent_root && !sctx->cur_inode_new &&
@@ -2113,6 +2171,14 @@ static int get_cur_path(struct send_ctx *sctx, u64 ino, u64 gen,
 	while (!stop && ino != BTRFS_FIRST_FREE_OBJECTID) {
 		fs_path_reset(name);
 
+		if (is_waiting_for_rm(sctx, ino)) {
+			ret = gen_unique_name(sctx, ino, gen, name);
+			if (ret < 0)
+				goto out;
+			ret = fs_path_add_path(dest, name);
+			break;
+		}
+
 		ret = __get_cur_name_and_parent(sctx, ino, gen, skip_name_cache,
 				&parent_inode, &parent_gen, name);
 		if (ret < 0)
@@ -2641,12 +2707,78 @@ static int orphanize_inode(struct send_ctx *sctx, u64 ino, u64 gen,
 	return ret;
 }
 
+static struct orphan_dir_info *
+add_orphan_dir_info(struct send_ctx *sctx, u64 dir_ino)
+{
+	struct rb_node **p = &sctx->orphan_dirs.rb_node;
+	struct rb_node *parent = NULL;
+	struct orphan_dir_info *entry, *odi;
+
+	odi = kmalloc(sizeof(*odi), GFP_NOFS);
+	if (!odi)
+		return ERR_PTR(-ENOMEM);
+	odi->ino = dir_ino;
+	odi->gen = 0;
+
+	while (*p) {
+		parent = *p;
+		entry = rb_entry(parent, struct orphan_dir_info, node);
+		if (dir_ino < entry->ino) {
+			p = &(*p)->rb_left;
+		} else if (dir_ino > entry->ino) {
+			p = &(*p)->rb_right;
+		} else {
+			kfree(odi);
+			return entry;
+		}
+	}
+
+	rb_link_node(&odi->node, parent, p);
+	rb_insert_color(&odi->node, &sctx->orphan_dirs);
+	return odi;
+}
+
+static struct orphan_dir_info *
+get_orphan_dir_info(struct send_ctx *sctx, u64 dir_ino)
+{
+	struct rb_node *n = sctx->orphan_dirs.rb_node;
+	struct orphan_dir_info *entry;
+
+	while (n) {
+		entry = rb_entry(n, struct orphan_dir_info, node);
+		if (dir_ino < entry->ino)
+			n = n->rb_left;
+		else if (dir_ino > entry->ino)
+			n = n->rb_right;
+		else
+			return entry;
+	}
+	return NULL;
+}
+
+static int is_waiting_for_rm(struct send_ctx *sctx, u64 dir_ino)
+{
+	struct orphan_dir_info *odi = get_orphan_dir_info(sctx, dir_ino);
+
+	return odi != NULL;
+}
+
+static void free_orphan_dir_info(struct send_ctx *sctx,
+				 struct orphan_dir_info *odi)
+{
+	if (!odi)
+		return;
+	rb_erase(&odi->node, &sctx->orphan_dirs);
+	kfree(odi);
+}
+
 /*
  * Returns 1 if a directory can be removed at this point in time.
  * We check this by iterating all dir items and checking if the inode behind
  * the dir item was already processed.
  */
-static int can_rmdir(struct send_ctx *sctx, u64 dir, u64 send_progress)
+static int can_rmdir(struct send_ctx *sctx, u64 dir, u64 dir_gen,
+		     u64 send_progress)
 {
 	int ret = 0;
 	struct btrfs_root *root = sctx->parent_root;
@@ -2674,6 +2806,8 @@ static int can_rmdir(struct send_ctx *sctx, u64 dir, u64 send_progress)
 		goto out;
 
 	while (1) {
+		struct waiting_dir_move *dm;
+
 		if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
 			ret = btrfs_next_leaf(root, path);
 			if (ret < 0)
@@ -2692,6 +2826,21 @@ static int can_rmdir(struct send_ctx *sctx, u64 dir, u64 send_progress)
 				struct btrfs_dir_item);
 		btrfs_dir_item_key_to_cpu(path->nodes[0], di, &loc);
 
+		dm = get_waiting_dir_move(sctx, loc.objectid);
+		if (dm) {
+			struct orphan_dir_info *odi;
+
+			odi = add_orphan_dir_info(sctx, dir);
+			if (IS_ERR(odi)) {
+				ret = PTR_ERR(odi);
+				goto out;
+			}
+			odi->gen = dir_gen;
+			dm->rmdir_ino = dir;
+			ret = 0;
+			goto out;
+		}
+
 		if (loc.objectid > send_progress) {
 			ret = 0;
 			goto out;
@@ -2709,19 +2858,9 @@ static int can_rmdir(struct send_ctx *sctx, u64 dir, u64 send_progress)
 
 static int is_waiting_for_move(struct send_ctx *sctx, u64 ino)
 {
-	struct rb_node *n = sctx->waiting_dir_moves.rb_node;
-	struct waiting_dir_move *entry;
+	struct waiting_dir_move *entry = get_waiting_dir_move(sctx, ino);
 
-	while (n) {
-		entry = rb_entry(n, struct waiting_dir_move, node);
-		if (ino < entry->ino)
-			n = n->rb_left;
-		else if (ino > entry->ino)
-			n = n->rb_right;
-		else
-			return 1;
-	}
-	return 0;
+	return entry != NULL;
 }
 
 static int add_waiting_dir_move(struct send_ctx *sctx, u64 ino)
@@ -2734,6 +2873,7 @@ static int add_waiting_dir_move(struct send_ctx *sctx, u64 ino)
 	if (!dm)
 		return -ENOMEM;
 	dm->ino = ino;
+	dm->rmdir_ino = 0;
 
 	while (*p) {
 		parent = *p;
@@ -2753,24 +2893,31 @@ static int add_waiting_dir_move(struct send_ctx *sctx, u64 ino)
 	return 0;
 }
 
-static int del_waiting_dir_move(struct send_ctx *sctx, u64 ino)
+static struct waiting_dir_move *
+get_waiting_dir_move(struct send_ctx *sctx, u64 ino)
 {
 	struct rb_node *n = sctx->waiting_dir_moves.rb_node;
 	struct waiting_dir_move *entry;
 
 	while (n) {
 		entry = rb_entry(n, struct waiting_dir_move, node);
-		if (ino < entry->ino) {
+		if (ino < entry->ino)
 			n = n->rb_left;
-		} else if (ino > entry->ino) {
+		else if (ino > entry->ino)
 			n = n->rb_right;
-		} else {
-			rb_erase(&entry->node, &sctx->waiting_dir_moves);
-			kfree(entry);
-			return 0;
-		}
+		else
+			return entry;
 	}
-	return -ENOENT;
+	return NULL;
+}
+
+static void free_waiting_dir_move(struct send_ctx *sctx,
+				  struct waiting_dir_move *dm)
+{
+	if (!dm)
+		return;
+	rb_erase(&dm->node, &sctx->waiting_dir_moves);
+	kfree(dm);
 }
 
 static int add_pending_dir_move(struct send_ctx *sctx, u64 parent_ino)
@@ -2861,6 +3008,8 @@ static int apply_dir_move(struct send_ctx *sctx, struct pending_dir_move *pm)
 	u64 orig_progress = sctx->send_progress;
 	struct recorded_ref *cur;
 	u64 parent_ino, parent_gen;
+	struct waiting_dir_move *dm = NULL;
+	u64 rmdir_ino = 0;
 	int ret;
 
 	name = fs_path_alloc();
@@ -2870,8 +3019,10 @@ static int apply_dir_move(struct send_ctx *sctx, struct pending_dir_move *pm)
 		goto out;
 	}
 
-	ret = del_waiting_dir_move(sctx, pm->ino);
-	ASSERT(ret == 0);
+	dm = get_waiting_dir_move(sctx, pm->ino);
+	ASSERT(dm);
+	rmdir_ino = dm->rmdir_ino;
+	free_waiting_dir_move(sctx, dm);
 
 	ret = get_first_ref(sctx->parent_root, pm->ino,
 			    &parent_ino, &parent_gen, name);
@@ -2914,6 +3065,35 @@ static int apply_dir_move(struct send_ctx *sctx, struct pending_dir_move *pm)
 	if (ret < 0)
 		goto out;
 
+	if (rmdir_ino) {
+		struct orphan_dir_info *odi;
+
+		odi = get_orphan_dir_info(sctx, rmdir_ino);
+		if (!odi) {
+			/* already deleted */
+			goto finish;
+		}
+		ret = can_rmdir(sctx, rmdir_ino, odi->gen, sctx->cur_ino + 1);
+		if (ret < 0)
+			goto out;
+		if (!ret)
+			goto finish;
+
+		name = fs_path_alloc();
+		if (!name) {
+			ret = -ENOMEM;
+			goto out;
+		}
+		ret = get_cur_path(sctx, rmdir_ino, odi->gen, name);
+		if (ret < 0)
+			goto out;
+		ret = send_rmdir(sctx, name);
+		if (ret < 0)
+			goto out;
+		free_orphan_dir_info(sctx, odi);
+	}
+
+finish:
 	ret = send_utimes(sctx, pm->ino, pm->gen);
 	if (ret < 0)
 		goto out;
@@ -2923,6 +3103,8 @@ static int apply_dir_move(struct send_ctx *sctx, struct pending_dir_move *pm)
 	 * and old parent(s).
 	 */
 	list_for_each_entry(cur, &pm->update_refs, list) {
+		if (cur->dir == rmdir_ino)
+			continue;
 		ret = send_utimes(sctx, cur->dir, cur->dir_gen);
 		if (ret < 0)
 			goto out;
@@ -3259,7 +3441,8 @@ verbose_printk("btrfs: process_recorded_refs %llu\n", sctx->cur_ino);
 		 * later, we do this check again and rmdir it then if possible.
 		 * See the use of check_dirs for more details.
 		 */
-		ret = can_rmdir(sctx, sctx->cur_ino, sctx->cur_ino);
+		ret = can_rmdir(sctx, sctx->cur_ino, sctx->cur_inode_gen,
+				sctx->cur_ino);
 		if (ret < 0)
 			goto out;
 		if (ret) {
@@ -3352,7 +3535,8 @@ verbose_printk("btrfs: process_recorded_refs %llu\n", sctx->cur_ino);
 				goto out;
 		} else if (ret == inode_state_did_delete &&
 			   cur->dir != last_dir_ino_rm) {
-			ret = can_rmdir(sctx, cur->dir, sctx->cur_ino);
+			ret = can_rmdir(sctx, cur->dir, cur->dir_gen,
+					sctx->cur_ino);
 			if (ret < 0)
 				goto out;
 			if (ret) {
@@ -5389,6 +5573,7 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_)
 
 	sctx->pending_dir_moves = RB_ROOT;
 	sctx->waiting_dir_moves = RB_ROOT;
+	sctx->orphan_dirs = RB_ROOT;
 
 	sctx->clone_roots = vzalloc(sizeof(struct clone_root) *
 			(arg->clone_sources_count + 1));
@@ -5526,6 +5711,16 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_)
 		kfree(dm);
 	}
 
+	WARN_ON(sctx && !ret && !RB_EMPTY_ROOT(&sctx->orphan_dirs));
+	while (sctx && !RB_EMPTY_ROOT(&sctx->orphan_dirs)) {
+		struct rb_node *n;
+		struct orphan_dir_info *odi;
+
+		n = rb_first(&sctx->orphan_dirs);
+		odi = rb_entry(n, struct orphan_dir_info, node);
+		free_orphan_dir_info(sctx, odi);
+	}
+
 	if (sort_clone_roots) {
 		for (i = 0; i < sctx->clone_roots_cnt; i++)
 			btrfs_root_dec_send_in_progress(