Btrfs: incremental send, check if orphanized dir inode needs delayed rename

If a directory inode is orphanized, because some inode previously
processed has a new name that collides with the old name of the current
inode, we need to check if it needs its rename operation delayed too,
as its ancestor-descendent relationship with some other inode might
have been reversed between the parent and send snapshots and therefore
its rename operation needs to happen after that other inode is renamed.

For example, for the following reproducer where this is needed (provided
by Robbie Ko):

  $ mkfs.btrfs -f /dev/sdb
  $ mount /dev/sdb /mnt
  $ mkfs.btrfs -f /dev/sdc
  $ mount /dev/sdc /mnt2

  $ mkdir -p /mnt/data/n1/n2
  $ mkdir /mnt/data/n4
  $ mkdir -p /mnt/data/t6/t7
  $ mkdir /mnt/data/t5
  $ mkdir /mnt/data/t7
  $ mkdir /mnt/data/n4/t2
  $ mkdir /mnt/data/t4
  $ mkdir /mnt/data/t3
  $ mv /mnt/data/t7 /mnt/data/n4/t2
  $ mv /mnt/data/t4 /mnt/data/n4/t2/t7
  $ mv /mnt/data/t5 /mnt/data/n4/t2/t7/t4
  $ mv /mnt/data/t6 /mnt/data/n4/t2/t7/t4/t5
  $ mv /mnt/data/n1/n2 /mnt/data/n4/t2/t7/t4/t5/t6
  $ mv /mnt/data/n1 /mnt/data/n4/t2/t7/t4/t5/t6
  $ mv /mnt/data/n4/t2/t7/t4/t5/t6/t7 /mnt/data/n4/t2/t7/t4/t5/t6/n2
  $ mv /mnt/data/t3 /mnt/data/n4/t2/t7/t4/t5/t6/n2/t7

  $ btrfs subvolume snapshot -r /mnt /mnt/snap1

  $ mv /mnt/data/n4/t2/t7/t4/t5/t6/n1 /mnt/data/n4
  $ mv /mnt/data/n4/t2 /mnt/data/n4/n1
  $ mv /mnt/data/n4/n1/t2/t7/t4/t5/t6/n2 /mnt/data/n4/n1/t2
  $ mv /mnt/data/n4/n1/t2/n2/t7/t3 /mnt/data/n4/n1/t2
  $ mv /mnt/data/n4/n1/t2/t7/t4/t5/t6 /mnt/data/n4/n1/t2
  $ mv /mnt/data/n4/n1/t2/t7/t4 /mnt/data/n4/n1/t2/t6
  $ mv /mnt/data/n4/n1/t2/t7 /mnt/data/n4/n1/t2/t3
  $ mv /mnt/data/n4/n1/t2/n2/t7 /mnt/data/n4/n1/t2

  $ btrfs subvolume snapshot -r /mnt /mnt/snap2

  $ btrfs send /mnt/snap1 | btrfs receive /mnt2
  $ btrfs send -p /mnt/snap1 /mnt/snap2 | btrfs receive /mnt2
  ERROR: send ioctl failed with -12: Cannot allocate memory

Where the parent snapshot directory hierarchy is the following:

  .                                                        (ino 256)
  |-- data/                                                (ino 257)
        |-- n4/                                            (ino 260)
             |-- t2/                                       (ino 265)
                  |-- t7/                                  (ino 264)
                       |-- t4/                             (ino 266)
                            |-- t5/                        (ino 263)
                                 |-- t6/                   (ino 261)
                                      |-- n1/              (ino 258)
                                      |-- n2/              (ino 259)
                                           |-- t7/         (ino 262)
                                                |-- t3/    (ino 267)

And the send snapshot's directory hierarchy is the following:

  .                                                        (ino 256)
  |-- data/                                                (ino 257)
        |-- n4/                                            (ino 260)
             |-- n1/                                       (ino 258)
                  |-- t2/                                  (ino 265)
                       |-- n2/                             (ino 259)
                       |-- t3/                             (ino 267)
                       |    |-- t7                         (ino 264)
                       |
                       |-- t6/                             (ino 261)
                       |    |-- t4/                        (ino 266)
                       |         |-- t5/                   (ino 263)
                       |
                       |-- t7/                             (ino 262)

While processing inode 262 we orphanize inode 264 and later attempt
to rename inode 264 to its new name/location, which resulted in building
an incorrect destination path string for the rename operation with the
value "data/n4/t2/t7/t4/t5/t6/n2/t7/t3/t7". This rename operation must
have been done only after inode 267 is processed and renamed, as the
ancestor-descendent relationship between inodes 264 and 267 was reversed
between both snapshots, because otherwise it results in an infinite loop
when building the path string for inode 264 when we are processing an
inode with a number larger than 264. That loop is the following:

  start inode 264, send progress of 265 for example
  parent of 264 -> 267
  parent of 267 -> 262
  parent of 262 -> 259
  parent of 259 -> 261
  parent of 261 -> 263
  parent of 263 -> 266
  parent of 266 -> 264
    |--> back to first iteration while current path string length
         is <= PATH_MAX, and fail with -ENOMEM otherwise

So fix this by making the check if we need to delay a directory rename
regardless of the current inode having been orphanized or not.

A test case for fstests follows soon.

Thanks to Robbie Ko for providing a reproducer for this problem.
Reported-by: NRobbie Ko <robbieko@synology.com>
Signed-off-by: NFilipe Manana <fdmanana@suse.com>

fs/btrfs/send.c

@@ -243,6 +243,7 @@ struct waiting_dir_move {
 	 * after this directory is moved, we can try to rmdir the ino rmdir_ino.
 	 */
 	u64 rmdir_ino;
+	bool orphanized;
 };
 
 struct orphan_dir_info {
@@ -1900,8 +1901,13 @@ static int did_overwrite_ref(struct send_ctx *sctx,
 		goto out;
 	}
 
-	/* we know that it is or will be overwritten. check this now */
-	if (ow_inode < sctx->send_progress)
+	/*
+	 * We know that it is or will be overwritten. Check this now.
+	 * The current inode being processed might have been the one that caused
+	 * inode 'ino' to be orphanized, therefore ow_inode can actually be the
+	 * same as sctx->send_progress.
+	 */
+	if (ow_inode <= sctx->send_progress)
 		ret = 1;
 	else
 		ret = 0;
@@ -2223,6 +2229,8 @@ static int get_cur_path(struct send_ctx *sctx, u64 ino, u64 gen,
 	fs_path_reset(dest);
 
 	while (!stop && ino != BTRFS_FIRST_FREE_OBJECTID) {
+		struct waiting_dir_move *wdm;
+
 		fs_path_reset(name);
 
 		if (is_waiting_for_rm(sctx, ino)) {
@@ -2233,7 +2241,11 @@ static int get_cur_path(struct send_ctx *sctx, u64 ino, u64 gen,
 			break;
 		}
 
-		if (is_waiting_for_move(sctx, ino)) {
+		wdm = get_waiting_dir_move(sctx, ino);
+		if (wdm && wdm->orphanized) {
+			ret = gen_unique_name(sctx, ino, gen, name);
+			stop = 1;
+		} else if (wdm) {
 			ret = get_first_ref(sctx->parent_root, ino,
 					    &parent_inode, &parent_gen, name);
 		} else {
@@ -2923,7 +2935,7 @@ static int is_waiting_for_move(struct send_ctx *sctx, u64 ino)
 	return entry != NULL;
 }
 
-static int add_waiting_dir_move(struct send_ctx *sctx, u64 ino)
+static int add_waiting_dir_move(struct send_ctx *sctx, u64 ino, bool orphanized)
 {
 	struct rb_node **p = &sctx->waiting_dir_moves.rb_node;
 	struct rb_node *parent = NULL;
@@ -2934,6 +2946,7 @@ static int add_waiting_dir_move(struct send_ctx *sctx, u64 ino)
 		return -ENOMEM;
 	dm->ino = ino;
 	dm->rmdir_ino = 0;
+	dm->orphanized = orphanized;
 
 	while (*p) {
 		parent = *p;
@@ -3030,7 +3043,7 @@ static int add_pending_dir_move(struct send_ctx *sctx,
 			goto out;
 	}
 
-	ret = add_waiting_dir_move(sctx, pm->ino);
+	ret = add_waiting_dir_move(sctx, pm->ino, is_orphan);
 	if (ret)
 		goto out;
 
@@ -3385,7 +3398,8 @@ static int is_ancestor(struct btrfs_root *root,
 }
 
 static int wait_for_parent_move(struct send_ctx *sctx,
-				struct recorded_ref *parent_ref)
+				struct recorded_ref *parent_ref,
+				const bool is_orphan)
 {
 	int ret = 0;
 	u64 ino = parent_ref->dir;
@@ -3464,7 +3478,7 @@ static int wait_for_parent_move(struct send_ctx *sctx,
 					   ino,
 					   &sctx->new_refs,
 					   &sctx->deleted_refs,
-					   false);
+					   is_orphan);
 		if (!ret)
 			ret = 1;
 	}
@@ -3633,6 +3647,17 @@ verbose_printk("btrfs: process_recorded_refs %llu\n", sctx->cur_ino);
 			}
 		}
 
+		if (S_ISDIR(sctx->cur_inode_mode) && sctx->parent_root &&
+		    can_rename) {
+			ret = wait_for_parent_move(sctx, cur, is_orphan);
+			if (ret < 0)
+				goto out;
+			if (ret == 1) {
+				can_rename = false;
+				*pending_move = 1;
+			}
+		}
+
 		/*
 		 * link/move the ref to the new place. If we have an orphan
 		 * inode, move it and update valid_path. If not, link or move
@@ -3653,18 +3678,11 @@ verbose_printk("btrfs: process_recorded_refs %llu\n", sctx->cur_ino);
 				 * dirs, we always have one new and one deleted
 				 * ref. The deleted ref is ignored later.
 				 */
-				ret = wait_for_parent_move(sctx, cur);
-				if (ret < 0)
-					goto out;
-				if (ret) {
-					*pending_move = 1;
-				} else {
-					ret = send_rename(sctx, valid_path,
-							  cur->full_path);
-					if (!ret)
-						ret = fs_path_copy(valid_path,
-							       cur->full_path);
-				}
+				ret = send_rename(sctx, valid_path,
+						  cur->full_path);
+				if (!ret)
+					ret = fs_path_copy(valid_path,
+							   cur->full_path);
 				if (ret < 0)
 					goto out;
 			} else {