This commit enables the delayed refs infrastructures. This entails doing
the following:

1. Replacing existing calls of btrfs_extent_post_op (which is the
equivalent of delayed refs) with the proper btrfs_run_delayed_refs.
As well as eliminating open-coded calls to finish_current_insert and
del_pending_extents which execute the delayed ops.

2. Wiring up the addition of delayed refs when freeing extents
(btrfs_free_extent) and when adding new extents (alloc_tree_block).

3. Adding calls to btrfs_run_delayed refs in the transaction commit
path alongside comments why every call is needed, since it's not always
obvious (those call sites were derived empirically by running and
debugging existing tests)

4. Correctly flagging the transaction in which we are reinitialising
the extent tree.

Signed-off-by: Nikolay Borisov <redacted>
---
 check/main.c  |   3 +-
 extent-tree.c | 166 ++++++++++++++++++++++++++++++----------------------------
 transaction.c |  24 +++++++++
 3 files changed, 111 insertions(+), 82 deletions(-)

diff --git a/check/main.c b/check/main.c
index b84903acdb25..7c9689f29fd3 100644
--- a/check/main.c
+++ b/check/main.c

@@ -8634,7 +8634,7 @@ static int reinit_extent_tree(struct btrfs_trans_handle *trans,
 			fprintf(stderr, "Error adding block group\n");
 			return ret;
 		}
-		btrfs_extent_post_op(trans);
+		btrfs_run_delayed_refs(trans, -1);
 	}
 
 	ret = reset_balance(trans, fs_info);

@@ -9682,6 +9682,7 @@ int cmd_check(int argc, char **argv)
 			goto close_out;
 		}
 
+		trans->reinit_extent_tree = true;
 		if (init_extent_tree) {
 			printf("Creating a new extent tree\n");
 			ret = reinit_extent_tree(trans, info,

diff --git a/extent-tree.c b/extent-tree.c
index 3208ed11cb91..9d085158f2d8 100644
--- a/extent-tree.c
+++ b/extent-tree.c

@@ -1418,8 +1418,6 @@ int btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
 		err = ret;
 out:
 	btrfs_free_path(path);
-	finish_current_insert(trans);
-	del_pending_extents(trans);
 	BUG_ON(err);
 	return err;
 }

@@ -1602,8 +1600,6 @@ int btrfs_set_block_flags(struct btrfs_trans_handle *trans, u64 bytenr,
 	btrfs_set_extent_flags(l, item, flags);
 out:
 	btrfs_free_path(path);
-	finish_current_insert(trans);
-	del_pending_extents(trans);
 	return ret;
 }
 

@@ -1701,7 +1697,6 @@ static int write_one_cache_group(struct btrfs_trans_handle *trans,
 				 struct btrfs_block_group_cache *cache)
 {
 	int ret;
-	int pending_ret;
 	struct btrfs_root *extent_root = trans->fs_info->extent_root;
 	unsigned long bi;
 	struct extent_buffer *leaf;

@@ -1717,12 +1712,8 @@ static int write_one_cache_group(struct btrfs_trans_handle *trans,
 	btrfs_mark_buffer_dirty(leaf);
 	btrfs_release_path(path);
 fail:
-	finish_current_insert(trans);
-	pending_ret = del_pending_extents(trans);
 	if (ret)
 		return ret;
-	if (pending_ret)
-		return pending_ret;
 	return 0;
 
 }

@@ -2050,6 +2041,7 @@ static int finish_current_insert(struct btrfs_trans_handle *trans)
 	int skinny_metadata =
 		btrfs_fs_incompat(extent_root->fs_info, SKINNY_METADATA);
 
+
 	while(1) {
 		ret = find_first_extent_bit(&info->extent_ins, 0, &start,
 					    &end, EXTENT_LOCKED);

@@ -2081,6 +2073,8 @@ static int finish_current_insert(struct btrfs_trans_handle *trans)
 			BUG_ON(1);
 		}
 
+
+		printf("shouldn't be executed\n");
 		clear_extent_bits(&info->extent_ins, start, end, EXTENT_LOCKED);
 		kfree(extent_op);
 	}

@@ -2380,7 +2374,6 @@ static int __free_extent(struct btrfs_trans_handle *trans,
 	}
 fail:
 	btrfs_free_path(path);
-	finish_current_insert(trans);
 	return ret;
 }
 

@@ -2463,33 +2456,30 @@ int btrfs_free_extent(struct btrfs_trans_handle *trans,
 		      u64 bytenr, u64 num_bytes, u64 parent,
 		      u64 root_objectid, u64 owner, u64 offset)
 {
-	struct btrfs_root *extent_root = root->fs_info->extent_root;
-	int pending_ret;
 	int ret;
 
 	WARN_ON(num_bytes < root->fs_info->sectorsize);
-	if (root == extent_root) {
-		struct pending_extent_op *extent_op;
-
-		extent_op = kmalloc(sizeof(*extent_op), GFP_NOFS);
-		BUG_ON(!extent_op);
-
-		extent_op->type = PENDING_EXTENT_DELETE;
-		extent_op->bytenr = bytenr;
-		extent_op->num_bytes = num_bytes;
-		extent_op->level = (int)owner;
-
-		set_extent_bits(&root->fs_info->pending_del,
-				bytenr, bytenr + num_bytes - 1,
-				EXTENT_LOCKED);
-		set_state_private(&root->fs_info->pending_del,
-				  bytenr, (unsigned long)extent_op);
-		return 0;
+	/*
+	 * tree log blocks never actually go into the extent allocation
+	 * tree, just update pinning info and exit early.
+	 */
+	if (root_objectid == BTRFS_TREE_LOG_OBJECTID) {
+		printf("PINNING EXTENTS IN LOG TREE\n");
+		WARN_ON(owner >= BTRFS_FIRST_FREE_OBJECTID);
+		btrfs_pin_extent(trans->fs_info, bytenr, num_bytes);
+		ret = 0;
+	} else if (owner < BTRFS_FIRST_FREE_OBJECTID) {
+		BUG_ON(offset);
+		ret = btrfs_add_delayed_tree_ref(trans->fs_info, trans,
+						 bytenr, num_bytes, parent,
+						 root_objectid, (int)owner,
+						 BTRFS_DROP_DELAYED_REF,
+						 NULL, NULL, NULL);
+	} else {
+		ret = __free_extent(trans, bytenr, num_bytes, parent,
+				    root_objectid, owner, offset, 1);
 	}
-	ret = __free_extent(trans, root, bytenr, num_bytes, parent,
-			    root_objectid, owner, offset, 1);
-	pending_ret = del_pending_extents(trans);
-	return ret ? ret : pending_ret;
+	return ret;
 }
 
 static u64 stripe_align(struct btrfs_root *root, u64 val)

@@ -2695,6 +2685,8 @@ static int alloc_reserved_tree_block2(struct btrfs_trans_handle *trans,
 	struct btrfs_delayed_tree_ref *ref = btrfs_delayed_node_to_tree_ref(node);
 	struct btrfs_key ins;
 	bool skinny_metadata = btrfs_fs_incompat(trans->fs_info, SKINNY_METADATA);
+	int ret;
+	u64 start, end;
 
 	ins.objectid = node->bytenr;
 	if (skinny_metadata) {

@@ -2705,10 +2697,25 @@ static int alloc_reserved_tree_block2(struct btrfs_trans_handle *trans,
 		ins.type = BTRFS_EXTENT_ITEM_KEY;
 	}
 
-	return alloc_reserved_tree_block(trans, ref->root, trans->transid,
-					 extent_op->flags_to_set,
-					 &extent_op->key, ref->level, &ins);
+	if (ref->root == BTRFS_EXTENT_TREE_OBJECTID) {
+		ret = find_first_extent_bit(&trans->fs_info->extent_ins,
+					    node->bytenr, &start, &end,
+					    EXTENT_LOCKED);
+		ASSERT(!ret);
+		ASSERT(start == node->bytenr);
+		ASSERT(end == node->bytenr + node->num_bytes - 1);
+	}
+
+	ret = alloc_reserved_tree_block(trans, ref->root, trans->transid,
+					extent_op->flags_to_set,
+					&extent_op->key, ref->level, &ins);
 
+	if (ref->root == BTRFS_EXTENT_TREE_OBJECTID) {
+		clear_extent_bits(&trans->fs_info->extent_ins, start, end,
+				  EXTENT_LOCKED);
+	}
+
+	return ret;
 }
 
 static int alloc_reserved_tree_block(struct btrfs_trans_handle *trans,

@@ -2773,39 +2780,50 @@ static int alloc_tree_block(struct btrfs_trans_handle *trans,
 			    u64 search_end, struct btrfs_key *ins)
 {
 	int ret;
+	u64 extent_size;
+	struct btrfs_delayed_extent_op *extent_op;
+	bool skinny_metadata = btrfs_fs_incompat(root->fs_info,
+						 SKINNY_METADATA);
+
+	extent_op = btrfs_alloc_delayed_extent_op();
+	if (!extent_op)
+		return -ENOMEM;
+
 	ret = btrfs_reserve_extent(trans, root, num_bytes, empty_size,
 				   hint_byte, search_end, ins, 0);
 	BUG_ON(ret);
 
+	if (key)
+		memcpy(&extent_op->key, key, sizeof(extent_op->key));
+	else
+		memset(&extent_op->key, 0, sizeof(extent_op->key));
+	extent_op->flags_to_set = flags;
+	extent_op->update_key = skinny_metadata ? false : true;
+	extent_op->update_flags = true;
+	extent_op->is_data = false;
+	extent_op->level = level;
+
+	extent_size = ins->offset;
+
+	if (btrfs_fs_incompat(root->fs_info, SKINNY_METADATA)) {
+		ins->offset = level;
+		ins->type = BTRFS_METADATA_ITEM_KEY;
+	}
+
+	/* Ensure this reserved extent is not found by the allocator */
 	if (root_objectid == BTRFS_EXTENT_TREE_OBJECTID) {
-		struct pending_extent_op *extent_op;
-
-		extent_op = kmalloc(sizeof(*extent_op), GFP_NOFS);
-		BUG_ON(!extent_op);
-
-		extent_op->type = PENDING_EXTENT_INSERT;
-		extent_op->bytenr = ins->objectid;
-		extent_op->num_bytes = ins->offset;
-		extent_op->level = level;
-		extent_op->flags = flags;
-		memcpy(&extent_op->key, key, sizeof(*key));
-
-		set_extent_bits(&root->fs_info->extent_ins, ins->objectid,
-				ins->objectid + ins->offset - 1,
-				EXTENT_LOCKED);
-		set_state_private(&root->fs_info->extent_ins,
-				  ins->objectid, (unsigned long)extent_op);
-	} else {
-		if (btrfs_fs_incompat(root->fs_info, SKINNY_METADATA)) {
-			ins->offset = level;
-			ins->type = BTRFS_METADATA_ITEM_KEY;
-		}
-		ret = alloc_reserved_tree_block(trans, root, root_objectid,
-						generation, flags,
-						key, level, ins);
-		finish_current_insert(trans);
-		del_pending_extents(trans);
+		ret = set_extent_bits(&trans->fs_info->extent_ins,
+				      ins->objectid,
+				      ins->objectid + extent_size - 1,
+				      EXTENT_LOCKED);
+
+		BUG_ON(ret);
 	}
+
+	ret = btrfs_add_delayed_tree_ref(root->fs_info, trans, ins->objectid,
+					 extent_size, 0, root_objectid,
+					 level, BTRFS_ADD_DELAYED_EXTENT,
+					 extent_op, NULL, NULL);
 	return ret;
 }
 

@@ -3330,11 +3348,6 @@ int btrfs_make_block_group(struct btrfs_trans_handle *trans,
 				sizeof(cache->item));
 	BUG_ON(ret);
 
-	ret = finish_current_insert(trans);
-	BUG_ON(ret);
-	ret = del_pending_extents(trans);
-	BUG_ON(ret);
-
 	return 0;
 }
 

@@ -3430,10 +3443,6 @@ int btrfs_make_block_groups(struct btrfs_trans_handle *trans,
 					sizeof(cache->item));
 		BUG_ON(ret);
 
-		finish_current_insert(trans);
-		ret = del_pending_extents(trans);
-		BUG_ON(ret);
-
 		cur_start = cache->key.objectid + cache->key.offset;
 	}
 	return 0;

@@ -3815,14 +3824,9 @@ int btrfs_fix_block_accounting(struct btrfs_trans_handle *trans)
 	struct btrfs_fs_info *fs_info = trans->fs_info;
 	struct btrfs_root *root = fs_info->extent_root;
 
-	while(extent_root_pending_ops(fs_info)) {
-		ret = finish_current_insert(trans);
-		if (ret)
-			return ret;
-		ret = del_pending_extents(trans);
-		if (ret)
-			return ret;
-	}
+	ret = btrfs_run_delayed_refs(trans, -1);
+	if (ret)
+		return ret;
 
 	while(1) {
 		cache = btrfs_lookup_first_block_group(fs_info, start);

@@ -4027,7 +4031,7 @@ static int __btrfs_record_file_extent(struct btrfs_trans_handle *trans,
 		} else if (ret != -EEXIST) {
 			goto fail;
 		}
-		btrfs_extent_post_op(trans);
+		btrfs_run_delayed_refs(trans, -1);
 		extent_bytenr = disk_bytenr;
 		extent_num_bytes = num_bytes;
 		extent_offset = 0;

diff --git a/transaction.c b/transaction.c
index ecafbb156610..b2d613ee88d0 100644
--- a/transaction.c
+++ b/transaction.c

@@ -98,6 +98,17 @@ int commit_tree_roots(struct btrfs_trans_handle *trans,
 	if (ret)
 		return ret;
 
+	/*
+	 * If the above CoW is the first one to dirty the current tree_root,
+	 * delayed refs for it won't be run until after this function has
+	 * finished executing, meaning we won't process the extent tree root,
+	 * which will have been added to ->dirty_cowonly_roots.  So run
+	 * delayed refs here as well.
+	 */
+	ret = btrfs_run_delayed_refs(trans, -1);
+	if (ret)
+		return ret;
+
 	while(!list_empty(&fs_info->dirty_cowonly_roots)) {
 		next = fs_info->dirty_cowonly_roots.next;
 		list_del_init(next);

@@ -147,6 +158,12 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 
 	if (trans->fs_info->transaction_aborted)
 		return -EROFS;
+	/*
+	 * Flush all accumulated delayed refs so that root-tree updates are
+	 * consistent
+	 */
+	ret = btrfs_run_delayed_refs(trans, -1);
+	BUG_ON(ret);
 
 	if (root->commit_root == root->node)
 		goto commit_tree;

@@ -164,9 +181,16 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 	ret = btrfs_update_root(trans, root->fs_info->tree_root,
 				&root->root_key, &root->root_item);
 	BUG_ON(ret);
+
 commit_tree:
 	ret = commit_tree_roots(trans, fs_info);
 	BUG_ON(ret);
+	/*
+	 * Ensure that all comitted roots are properly accounted in the
+	 * extent tree
+	 */
+	ret = btrfs_run_delayed_refs(trans, -1);
+	BUG_ON(ret);