Btrfs: add a extent ref verify tool

We were having corruption issues that were tied back to problems with
the extent tree.  In order to track them down I built this tool to try
and find the culprit, which was pretty successful.  If you compile with
this tool on it will live verify every ref update that the fs makes and
make sure it is consistent and valid.  I've run this through with
xfstests and haven't gotten any false positives.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update error messages, add fixup from Dan Carpenter to handle errors
  of read_tree_block ]
Signed-off-by: David Sterba <dsterba@suse.com>

7 files changed, 1138 insertions, 0 deletions

diff --git a/fs/btrfs/Kconfig b/fs/btrfs/Kconfig
index a26c63b4ad68..2e558227931a 100644
--- a/fs/btrfs/Kconfig
+++ b/fs/btrfs/Kconfig
@@ -91,3 +91,14 @@ config BTRFS_ASSERT
 	  any of the assertions trip.  This is meant for btrfs developers only.
 
 	  If unsure, say N.
+
+config BTRFS_FS_REF_VERIFY
+	bool "Btrfs with the ref verify tool compiled in"
+	depends on BTRFS_FS
+	default n
+	help
+	  Enable run-time extent reference verification instrumentation.  This
+	  is meant to be used by btrfs developers for tracking down extent
+	  reference problems or verifying they didn't break something.
+
+	  If unsure, say N.
diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
index 88255e133ade..9216ff22d741 100644
--- a/fs/btrfs/Makefile
+++ b/fs/btrfs/Makefile
@@ -13,6 +13,7 @@ btrfs-y += super.o ctree.o extent-tree.o print-tree.o root-tree.o dir-item.o \
 
 btrfs-$(CONFIG_BTRFS_FS_POSIX_ACL) += acl.o
 btrfs-$(CONFIG_BTRFS_FS_CHECK_INTEGRITY) += check-integrity.o
+btrfs-$(CONFIG_BTRFS_FS_REF_VERIFY) += ref-verify.o
 
 btrfs-$(CONFIG_BTRFS_FS_RUN_SANITY_TESTS) += tests/free-space-tests.o \
 	tests/extent-buffer-tests.o tests/btrfs-tests.o \
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 2fcc3c30d471..e2afe524e25e 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1097,6 +1097,11 @@ struct btrfs_fs_info {
 	u32 nodesize;
 	u32 sectorsize;
 	u32 stripesize;
+
+#ifdef CONFIG_BTRFS_FS_REF_VERIFY
+	spinlock_t ref_verify_lock;
+	struct rb_root block_tree;
+#endif
 };
 
 static inline struct btrfs_fs_info *btrfs_sb(struct super_block *sb)
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index f3e6e8fa19b0..f971d5680e6f 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -51,6 +51,7 @@
 #include "qgroup.h"
 #include "compression.h"
 #include "tree-checker.h"
+#include "ref-verify.h"
 
 #ifdef CONFIG_X86
 #include <asm/cpufeature.h>
@@ -2509,6 +2510,7 @@ int open_ctree(struct super_block *sb,
 	/* readahead state */
 	INIT_RADIX_TREE(&fs_info->reada_tree, GFP_NOFS & ~__GFP_DIRECT_RECLAIM);
 	spin_lock_init(&fs_info->reada_lock);
+	btrfs_init_ref_verify(fs_info);
 
 	fs_info->thread_pool_size = min_t(unsigned long,
 					  num_online_cpus() + 2, 8);
@@ -2920,6 +2922,9 @@ retry_root_backup:
 	if (ret)
 		goto fail_trans_kthread;
 
+	if (btrfs_build_ref_tree(fs_info))
+		btrfs_err(fs_info, "couldn't build ref tree");
+
 	/* do not make disk changes in broken FS or nologreplay is given */
 	if (btrfs_super_log_root(disk_super) != 0 &&
 	    !btrfs_test_opt(fs_info, NOLOGREPLAY)) {
@@ -3785,6 +3790,7 @@ void close_ctree(struct btrfs_fs_info *fs_info)
 	cleanup_srcu_struct(&fs_info->subvol_srcu);
 
 	btrfs_free_stripe_hash_table(fs_info);
+	btrfs_free_ref_cache(fs_info);
 
 	__btrfs_free_block_rsv(root->orphan_block_rsv);
 	root->orphan_block_rsv = NULL;
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index a9787c3c0f7e..52d246994341 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -38,6 +38,7 @@
 #include "math.h"
 #include "sysfs.h"
 #include "qgroup.h"
+#include "ref-verify.h"
 
 #undef SCRAMBLE_DELAYED_REFS
 
@@ -2188,6 +2189,9 @@ int btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
 	BUG_ON(owner < BTRFS_FIRST_FREE_OBJECTID &&
 	       root_objectid == BTRFS_TREE_LOG_OBJECTID);
 
+	btrfs_ref_tree_mod(root, bytenr, num_bytes, parent, root_objectid,
+			   owner, offset, BTRFS_ADD_DELAYED_REF);
+
 	if (owner < BTRFS_FIRST_FREE_OBJECTID) {
 		ret = btrfs_add_delayed_tree_ref(fs_info, trans, bytenr,
 						 num_bytes, parent,
@@ -7280,6 +7284,10 @@ void btrfs_free_tree_block(struct btrfs_trans_handle *trans,
 	if (root->root_key.objectid != BTRFS_TREE_LOG_OBJECTID) {
 		int old_ref_mod, new_ref_mod;
 
+		btrfs_ref_tree_mod(root, buf->start, buf->len, parent,
+				   root->root_key.objectid,
+				   btrfs_header_level(buf), 0,
+				   BTRFS_DROP_DELAYED_REF);
 		ret = btrfs_add_delayed_tree_ref(fs_info, trans, buf->start,
 						 buf->len, parent,
 						 root->root_key.objectid,
@@ -7343,6 +7351,11 @@ int btrfs_free_extent(struct btrfs_trans_handle *trans,
 	if (btrfs_is_testing(fs_info))
 		return 0;
 
+	if (root_objectid != BTRFS_TREE_LOG_OBJECTID)
+		btrfs_ref_tree_mod(root, bytenr, num_bytes, parent,
+				   root_objectid, owner, offset,
+				   BTRFS_DROP_DELAYED_REF);
+
 	/*
 	 * tree log blocks never actually go into the extent allocation
 	 * tree, just update pinning info and exit early.
@@ -8318,6 +8331,10 @@ int btrfs_alloc_reserved_file_extent(struct btrfs_trans_handle *trans,
 
 	BUG_ON(root->root_key.objectid == BTRFS_TREE_LOG_OBJECTID);
 
+	btrfs_ref_tree_mod(root, ins->objectid, ins->offset, 0,
+			   root->root_key.objectid, owner, offset,
+			   BTRFS_ADD_DELAYED_EXTENT);
+
 	ret = btrfs_add_delayed_data_ref(fs_info, trans, ins->objectid,
 					 ins->offset, 0,
 					 root->root_key.objectid, owner,
@@ -8542,6 +8559,9 @@ struct extent_buffer *btrfs_alloc_tree_block(struct btrfs_trans_handle *trans,
 		extent_op->is_data = false;
 		extent_op->level = level;
 
+		btrfs_ref_tree_mod(root, ins.objectid, ins.offset, parent,
+				   root_objectid, level, 0,
+				   BTRFS_ADD_DELAYED_EXTENT);
 		ret = btrfs_add_delayed_tree_ref(fs_info, trans, ins.objectid,
 						 ins.offset, parent,
 						 root_objectid, level,
@@ -10391,6 +10411,8 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
 	 * remove it.
 	 */
 	free_excluded_extents(fs_info, block_group);
+	btrfs_free_ref_tree_range(fs_info, block_group->key.objectid,
+				  block_group->key.offset);
 
 	memcpy(&key, &block_group->key, sizeof(key));
 	index = get_block_group_index(block_group);
diff --git a/fs/btrfs/ref-verify.c b/fs/btrfs/ref-verify.c
new file mode 100644
index 000000000000..34878699d363
--- /dev/null
+++ b/fs/btrfs/ref-verify.c
@@ -0,0 +1,1031 @@
+/*
+ * Copyright (C) 2014 Facebook.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+#include <linux/sched.h>
+#include <linux/stacktrace.h>
+#include "ctree.h"
+#include "disk-io.h"
+#include "locking.h"
+#include "delayed-ref.h"
+#include "ref-verify.h"
+
+/*
+ * Used to keep track the roots and number of refs each root has for a given
+ * bytenr.  This just tracks the number of direct references, no shared
+ * references.
+ */
+struct root_entry {
+	u64 root_objectid;
+	u64 num_refs;
+	struct rb_node node;
+};
+
+/*
+ * These are meant to represent what should exist in the extent tree, these can
+ * be used to verify the extent tree is consistent as these should all match
+ * what the extent tree says.
+ */
+struct ref_entry {
+	u64 root_objectid;
+	u64 parent;
+	u64 owner;
+	u64 offset;
+	u64 num_refs;
+	struct rb_node node;
+};
+
+#define MAX_TRACE	16
+
+/*
+ * Whenever we add/remove a reference we record the action.  The action maps
+ * back to the delayed ref action.  We hold the ref we are changing in the
+ * action so we can account for the history properly, and we record the root we
+ * were called with since it could be different from ref_root.  We also store
+ * stack traces because thats how I roll.
+ */
+struct ref_action {
+	int action;
+	u64 root;
+	struct ref_entry ref;
+	struct list_head list;
+	unsigned long trace[MAX_TRACE];
+	unsigned int trace_len;
+};
+
+/*
+ * One of these for every block we reference, it holds the roots and references
+ * to it as well as all of the ref actions that have occured to it.  We never
+ * free it until we unmount the file system in order to make sure re-allocations
+ * are happening properly.
+ */
+struct block_entry {
+	u64 bytenr;
+	u64 len;
+	u64 num_refs;
+	int metadata;
+	int from_disk;
+	struct rb_root roots;
+	struct rb_root refs;
+	struct rb_node node;
+	struct list_head actions;
+};
+
+static struct block_entry *insert_block_entry(struct rb_root *root,
+					      struct block_entry *be)
+{
+	struct rb_node **p = &root->rb_node;
+	struct rb_node *parent_node = NULL;
+	struct block_entry *entry;
+
+	while (*p) {
+		parent_node = *p;
+		entry = rb_entry(parent_node, struct block_entry, node);
+		if (entry->bytenr > be->bytenr)
+			p = &(*p)->rb_left;
+		else if (entry->bytenr < be->bytenr)
+			p = &(*p)->rb_right;
+		else
+			return entry;
+	}
+
+	rb_link_node(&be->node, parent_node, p);
+	rb_insert_color(&be->node, root);
+	return NULL;
+}
+
+static struct block_entry *lookup_block_entry(struct rb_root *root, u64 bytenr)
+{
+	struct rb_node *n;
+	struct block_entry *entry = NULL;
+
+	n = root->rb_node;
+	while (n) {
+		entry = rb_entry(n, struct block_entry, node);
+		if (entry->bytenr < bytenr)
+			n = n->rb_right;
+		else if (entry->bytenr > bytenr)
+			n = n->rb_left;
+		else
+			return entry;
+	}
+	return NULL;
+}
+
+static struct root_entry *insert_root_entry(struct rb_root *root,
+					    struct root_entry *re)
+{
+	struct rb_node **p = &root->rb_node;
+	struct rb_node *parent_node = NULL;
+	struct root_entry *entry;
+
+	while (*p) {
+		parent_node = *p;
+		entry = rb_entry(parent_node, struct root_entry, node);
+		if (entry->root_objectid > re->root_objectid)
+			p = &(*p)->rb_left;
+		else if (entry->root_objectid < re->root_objectid)
+			p = &(*p)->rb_right;
+		else
+			return entry;
+	}
+
+	rb_link_node(&re->node, parent_node, p);
+	rb_insert_color(&re->node, root);
+	return NULL;
+
+}
+
+static int comp_refs(struct ref_entry *ref1, struct ref_entry *ref2)
+{
+	if (ref1->root_objectid < ref2->root_objectid)
+		return -1;
+	if (ref1->root_objectid > ref2->root_objectid)
+		return 1;
+	if (ref1->parent < ref2->parent)
+		return -1;
+	if (ref1->parent > ref2->parent)
+		return 1;
+	if (ref1->owner < ref2->owner)
+		return -1;
+	if (ref1->owner > ref2->owner)
+		return 1;
+	if (ref1->offset < ref2->offset)
+		return -1;
+	if (ref1->offset > ref2->offset)
+		return 1;
+	return 0;
+}
+
+static struct ref_entry *insert_ref_entry(struct rb_root *root,
+					  struct ref_entry *ref)
+{
+	struct rb_node **p = &root->rb_node;
+	struct rb_node *parent_node = NULL;
+	struct ref_entry *entry;
+	int cmp;
+
+	while (*p) {
+		parent_node = *p;
+		entry = rb_entry(parent_node, struct ref_entry, node);
+		cmp = comp_refs(entry, ref);
+		if (cmp > 0)
+			p = &(*p)->rb_left;
+		else if (cmp < 0)
+			p = &(*p)->rb_right;
+		else
+			return entry;
+	}
+
+	rb_link_node(&ref->node, parent_node, p);
+	rb_insert_color(&ref->node, root);
+	return NULL;
+
+}
+
+static struct root_entry *lookup_root_entry(struct rb_root *root, u64 objectid)
+{
+	struct rb_node *n;
+	struct root_entry *entry = NULL;
+
+	n = root->rb_node;
+	while (n) {
+		entry = rb_entry(n, struct root_entry, node);
+		if (entry->root_objectid < objectid)
+			n = n->rb_right;
+		else if (entry->root_objectid > objectid)
+			n = n->rb_left;
+		else
+			return entry;
+	}
+	return NULL;
+}
+
+#ifdef CONFIG_STACKTRACE
+static void __save_stack_trace(struct ref_action *ra)
+{
+	struct stack_trace stack_trace;
+
+	stack_trace.max_entries = MAX_TRACE;
+	stack_trace.nr_entries = 0;
+	stack_trace.entries = ra->trace;
+	stack_trace.skip = 2;
+	save_stack_trace(&stack_trace);
+	ra->trace_len = stack_trace.nr_entries;
+}
+
+static void __print_stack_trace(struct btrfs_fs_info *fs_info,
+				struct ref_action *ra)
+{
+	struct stack_trace trace;
+
+	if (ra->trace_len == 0) {
+		btrfs_err(fs_info, "  ref-verify: no stacktrace");
+		return;
+	}
+	trace.nr_entries = ra->trace_len;
+	trace.entries = ra->trace;
+	print_stack_trace(&trace, 2);
+}
+#else
+static void inline __save_stack_trace(struct ref_action *ra)
+{
+}
+
+static void inline __print_stack_trace(struct btrfs_fs_info *fs_info,
+				       struct ref_action *ra)
+{
+	btrfs_err(fs_info, "  ref-verify: no stacktrace support");
+}
+#endif
+
+static void free_block_entry(struct block_entry *be)
+{
+	struct root_entry *re;
+	struct ref_entry *ref;
+	struct ref_action *ra;
+	struct rb_node *n;
+
+	while ((n = rb_first(&be->roots))) {
+		re = rb_entry(n, struct root_entry, node);
+		rb_erase(&re->node, &be->roots);
+		kfree(re);
+	}
+
+	while((n = rb_first(&be->refs))) {
+		ref = rb_entry(n, struct ref_entry, node);
+		rb_erase(&ref->node, &be->refs);
+		kfree(ref);
+	}
+
+	while (!list_empty(&be->actions)) {
+		ra = list_first_entry(&be->actions, struct ref_action,
+				      list);
+		list_del(&ra->list);
+		kfree(ra);
+	}
+	kfree(be);
+}
+
+static struct block_entry *add_block_entry(struct btrfs_fs_info *fs_info,
+					   u64 bytenr, u64 len,
+					   u64 root_objectid)
+{
+	struct block_entry *be = NULL, *exist;
+	struct root_entry *re = NULL;
+
+	re = kzalloc(sizeof(struct root_entry), GFP_KERNEL);
+	be = kzalloc(sizeof(struct block_entry), GFP_KERNEL);
+	if (!be || !re) {
+		kfree(re);
+		kfree(be);
+		return ERR_PTR(-ENOMEM);
+	}
+	be->bytenr = bytenr;
+	be->len = len;
+
+	re->root_objectid = root_objectid;
+	re->num_refs = 0;
+
+	spin_lock(&fs_info->ref_verify_lock);
+	exist = insert_block_entry(&fs_info->block_tree, be);
+	if (exist) {
+		if (root_objectid) {
+			struct root_entry *exist_re;
+
+			exist_re = insert_root_entry(&exist->roots, re);
+			if (exist_re)
+				kfree(re);
+		}
+		kfree(be);
+		return exist;
+	}
+
+	be->num_refs = 0;
+	be->metadata = 0;
+	be->from_disk = 0;
+	be->roots = RB_ROOT;
+	be->refs = RB_ROOT;
+	INIT_LIST_HEAD(&be->actions);
+	if (root_objectid)
+		insert_root_entry(&be->roots, re);
+	else
+		kfree(re);
+	return be;
+}
+
+static int add_tree_block(struct btrfs_fs_info *fs_info, u64 ref_root,
+			  u64 parent, u64 bytenr, int level)
+{
+	struct block_entry *be;
+	struct root_entry *re;
+	struct ref_entry *ref = NULL, *exist;
+
+	ref = kmalloc(sizeof(struct ref_entry), GFP_KERNEL);
+	if (!ref)
+		return -ENOMEM;
+
+	if (parent)
+		ref->root_objectid = 0;
+	else
+		ref->root_objectid = ref_root;
+	ref->parent = parent;
+	ref->owner = level;
+	ref->offset = 0;
+	ref->num_refs = 1;
+
+	be = add_block_entry(fs_info, bytenr, fs_info->nodesize, ref_root);
+	if (IS_ERR(be)) {
+		kfree(ref);
+		return PTR_ERR(be);
+	}
+	be->num_refs++;
+	be->from_disk = 1;
+	be->metadata = 1;
+
+	if (!parent) {
+		ASSERT(ref_root);
+		re = lookup_root_entry(&be->roots, ref_root);
+		ASSERT(re);
+		re->num_refs++;
+	}
+	exist = insert_ref_entry(&be->refs, ref);
+	if (exist) {
+		exist->num_refs++;
+		kfree(ref);
+	}
+	spin_unlock(&fs_info->ref_verify_lock);
+
+	return 0;
+}
+
+static int add_shared_data_ref(struct btrfs_fs_info *fs_info,
+			       u64 parent, u32 num_refs, u64 bytenr,
+			       u64 num_bytes)
+{
+	struct block_entry *be;
+	struct ref_entry *ref;
+
+	ref = kzalloc(sizeof(struct ref_entry), GFP_KERNEL);
+	if (!ref)
+		return -ENOMEM;
+	be = add_block_entry(fs_info, bytenr, num_bytes, 0);
+	if (IS_ERR(be)) {
+		kfree(ref);
+		return PTR_ERR(be);
+	}
+	be->num_refs += num_refs;
+
+	ref->parent = parent;
+	ref->num_refs = num_refs;
+	if (insert_ref_entry(&be->refs, ref)) {
+		spin_unlock(&fs_info->ref_verify_lock);
+		btrfs_err(fs_info, "existing shared ref when reading from disk?");
+		kfree(ref);
+		return -EINVAL;
+	}
+	spin_unlock(&fs_info->ref_verify_lock);
+	return 0;
+}
+
+static int add_extent_data_ref(struct btrfs_fs_info *fs_info,
+			       struct extent_buffer *leaf,
+			       struct btrfs_extent_data_ref *dref,
+			       u64 bytenr, u64 num_bytes)
+{
+	struct block_entry *be;
+	struct ref_entry *ref;
+	struct root_entry *re;
+	u64 ref_root = btrfs_extent_data_ref_root(leaf, dref);
+	u64 owner = btrfs_extent_data_ref_objectid(leaf, dref);
+	u64 offset = btrfs_extent_data_ref_offset(leaf, dref);
+	u32 num_refs = btrfs_extent_data_ref_count(leaf, dref);
+
+	ref = kzalloc(sizeof(struct ref_entry), GFP_KERNEL);
+	if (!ref)
+		return -ENOMEM;
+	be = add_block_entry(fs_info, bytenr, num_bytes, ref_root);
+	if (IS_ERR(be)) {
+		kfree(ref);
+		return PTR_ERR(be);
+	}
+	be->num_refs += num_refs;
+
+	ref->parent = 0;
+	ref->owner = owner;
+	ref->root_objectid = ref_root;
+	ref->offset = offset;
+	ref->num_refs = num_refs;
+	if (insert_ref_entry(&be->refs, ref)) {
+		spin_unlock(&fs_info->ref_verify_lock);
+		btrfs_err(fs_info, "existing ref when reading from disk?");
+		kfree(ref);
+		return -EINVAL;
+	}
+
+	re = lookup_root_entry(&be->roots, ref_root);
+	if (!re) {
+		spin_unlock(&fs_info->ref_verify_lock);
+		btrfs_err(fs_info, "missing root in new block entry?");
+		return -EINVAL;
+	}
+	re->num_refs += num_refs;
+	spin_unlock(&fs_info->ref_verify_lock);
+	return 0;
+}
+
+static int process_extent_item(struct btrfs_fs_info *fs_info,
+			       struct btrfs_path *path, struct btrfs_key *key,
+			       int slot, int *tree_block_level)
+{
+	struct btrfs_extent_item *ei;
+	struct btrfs_extent_inline_ref *iref;
+	struct btrfs_extent_data_ref *dref;
+	struct btrfs_shared_data_ref *sref;
+	struct extent_buffer *leaf = path->nodes[0];
+	u32 item_size = btrfs_item_size_nr(leaf, slot);
+	unsigned long end, ptr;
+	u64 offset, flags, count;
+	int type, ret;
+
+	ei = btrfs_item_ptr(leaf, slot, struct btrfs_extent_item);
+	flags = btrfs_extent_flags(leaf, ei);
+
+	if ((key->type == BTRFS_EXTENT_ITEM_KEY) &&
+	    flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
+		struct btrfs_tree_block_info *info;
+
+		info = (struct btrfs_tree_block_info *)(ei + 1);
+		*tree_block_level = btrfs_tree_block_level(leaf, info);
+		iref = (struct btrfs_extent_inline_ref *)(info + 1);
+	} else {
+		if (key->type == BTRFS_METADATA_ITEM_KEY)
+			*tree_block_level = key->offset;
+		iref = (struct btrfs_extent_inline_ref *)(ei + 1);
+	}
+
+	ptr = (unsigned long)iref;
+	end = (unsigned long)ei + item_size;
+	while (ptr < end) {
+		iref = (struct btrfs_extent_inline_ref *)ptr;
+		type = btrfs_extent_inline_ref_type(leaf, iref);
+		offset = btrfs_extent_inline_ref_offset(leaf, iref);
+		switch (type) {
+		case BTRFS_TREE_BLOCK_REF_KEY:
+			ret = add_tree_block(fs_info, offset, 0, key->objectid,
+					     *tree_block_level);
+			break;
+		case BTRFS_SHARED_BLOCK_REF_KEY:
+			ret = add_tree_block(fs_info, 0, offset, key->objectid,
+					     *tree_block_level);
+			break;
+		case BTRFS_EXTENT_DATA_REF_KEY:
+			dref = (struct btrfs_extent_data_ref *)(&iref->offset);
+			ret = add_extent_data_ref(fs_info, leaf, dref,
+						  key->objectid, key->offset);
+			break;
+		case BTRFS_SHARED_DATA_REF_KEY:
+			sref = (struct btrfs_shared_data_ref *)(iref + 1);
+			count = btrfs_shared_data_ref_count(leaf, sref);
+			ret = add_shared_data_ref(fs_info, offset, count,
+						  key->objectid, key->offset);
+			break;
+		default:
+			btrfs_err(fs_info, "invalid key type in iref");
+			ret = -EINVAL;
+			break;
+		}
+		if (ret)
+			break;
+		ptr += btrfs_extent_inline_ref_size(type);
+	}
+	return ret;
+}
+
+static int process_leaf(struct btrfs_root *root,
+			struct btrfs_path *path, u64 *bytenr, u64 *num_bytes)
+{
+	struct btrfs_fs_info *fs_info = root->fs_info;
+	struct extent_buffer *leaf = path->nodes[0];
+	struct btrfs_extent_data_ref *dref;
+	struct btrfs_shared_data_ref *sref;
+	u32 count;
+	int i = 0, tree_block_level = 0, ret;
+	struct btrfs_key key;
+	int nritems = btrfs_header_nritems(leaf);
+
+	for (i = 0; i < nritems; i++) {
+		btrfs_item_key_to_cpu(leaf, &key, i);
+		switch (key.type) {
+		case BTRFS_EXTENT_ITEM_KEY:
+			*num_bytes = key.offset;
+		case BTRFS_METADATA_ITEM_KEY:
+			*bytenr = key.objectid;
+			ret = process_extent_item(fs_info, path, &key, i,
+						  &tree_block_level);
+			break;
+		case BTRFS_TREE_BLOCK_REF_KEY:
+			ret = add_tree_block(fs_info, key.offset, 0,
+					     key.objectid, tree_block_level);
+			break;
+		case BTRFS_SHARED_BLOCK_REF_KEY:
+			ret = add_tree_block(fs_info, 0, key.offset,
+					     key.objectid, tree_block_level);
+			break;
+		case BTRFS_EXTENT_DATA_REF_KEY:
+			dref = btrfs_item_ptr(leaf, i,
+					      struct btrfs_extent_data_ref);
+			ret = add_extent_data_ref(fs_info, leaf, dref, *bytenr,
+						  *num_bytes);
+			break;
+		case BTRFS_SHARED_DATA_REF_KEY:
+			sref = btrfs_item_ptr(leaf, i,
+					      struct btrfs_shared_data_ref);
+			count = btrfs_shared_data_ref_count(leaf, sref);
+			ret = add_shared_data_ref(fs_info, key.offset, count,
+						  *bytenr, *num_bytes);
+			break;
+		default:
+			break;
+		}
+		if (ret)
+			break;
+	}
+	return ret;
+}
+
+/* Walk down to the leaf from the given level */
+static int walk_down_tree(struct btrfs_root *root, struct btrfs_path *path,
+			  int level, u64 *bytenr, u64 *num_bytes)
+{
+	struct btrfs_fs_info *fs_info = root->fs_info;
+	struct extent_buffer *eb;
+	u64 block_bytenr, gen;
+	int ret = 0;
+
+	while (level >= 0) {
+		if (level) {
+			block_bytenr = btrfs_node_blockptr(path->nodes[level],
+							   path->slots[level]);
+			gen = btrfs_node_ptr_generation(path->nodes[level],
+							path->slots[level]);
+			eb = read_tree_block(fs_info, block_bytenr, gen);
+			if (IS_ERR(eb))
+				return PTR_ERR(eb);
+			if (!extent_buffer_uptodate(eb)) {
+				free_extent_buffer(eb);
+				return -EIO;
+			}
+			btrfs_tree_read_lock(eb);
+			btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
+			path->nodes[level-1] = eb;
+			path->slots[level-1] = 0;
+			path->locks[level-1] = BTRFS_READ_LOCK_BLOCKING;
+		} else {
+			ret = process_leaf(root, path, bytenr, num_bytes);
+			if (ret)
+				break;
+		}
+		level--;
+	}
+	return ret;
+}
+
+/* Walk up to the next node that needs to be processed */
+static int walk_up_tree(struct btrfs_root *root, struct btrfs_path *path,
+			int *level)
+{
+	int l;
+
+	for (l = 0; l < BTRFS_MAX_LEVEL; l++) {
+		if (!path->nodes[l])
+			continue;
+		if (l) {
+			path->slots[l]++;
+			if (path->slots[l] <
+			    btrfs_header_nritems(path->nodes[l])) {
+				*level = l;
+				return 0;
+			}
+		}
+		btrfs_tree_unlock_rw(path->nodes[l], path->locks[l]);
+		free_extent_buffer(path->nodes[l]);
+		path->nodes[l] = NULL;
+		path->slots[l] = 0;
+		path->locks[l] = 0;
+	}
+
+	return 1;
+}
+
+static void dump_ref_action(struct btrfs_fs_info *fs_info,
+			    struct ref_action *ra)
+{
+	btrfs_err(fs_info,
+"  Ref action %d, root %llu, ref_root %llu, parent %llu, owner %llu, offset %llu, num_refs %llu",
+		  ra->action, ra->root, ra->ref.root_objectid, ra->ref.parent,
+		  ra->ref.owner, ra->ref.offset, ra->ref.num_refs);
+	__print_stack_trace(fs_info, ra);
+}
+
+/*
+ * Dumps all the information from the block entry to printk, it's going to be
+ * awesome.
+ */
+static void dump_block_entry(struct btrfs_fs_info *fs_info,
+			     struct block_entry *be)
+{
+	struct ref_entry *ref;
+	struct root_entry *re;
+	struct ref_action *ra;
+	struct rb_node *n;
+
+	btrfs_err(fs_info,
+"dumping block entry [%llu %llu], num_refs %llu, metadata %d, from disk %d",
+		  be->bytenr, be->len, be->num_refs, be->metadata,
+		  be->from_disk);
+
+	for (n = rb_first(&be->refs); n; n = rb_next(n)) {
+		ref = rb_entry(n, struct ref_entry, node);
+		btrfs_err(fs_info,
+"  ref root %llu, parent %llu, owner %llu, offset %llu, num_refs %llu",
+			  ref->root_objectid, ref->parent, ref->owner,
+			  ref->offset, ref->num_refs);
+	}
+
+	for (n = rb_first(&be->roots); n; n = rb_next(n)) {
+		re = rb_entry(n, struct root_entry, node);
+		btrfs_err(fs_info, "  root entry %llu, num_refs %llu",
+			  re->root_objectid, re->num_refs);
+	}
+
+	list_for_each_entry(ra, &be->actions, list)
+		dump_ref_action(fs_info, ra);
+}
+
+/*
+ * btrfs_ref_tree_mod: called when we modify a ref for a bytenr
+ * @root: the root we are making this modification from.
+ * @bytenr: the bytenr we are modifying.
+ * @num_bytes: number of bytes.
+ * @parent: the parent bytenr.
+ * @ref_root: the original root owner of the bytenr.
+ * @owner: level in the case of metadata, inode in the case of data.
+ * @offset: 0 for metadata, file offset for data.
+ * @action: the action that we are doing, this is the same as the delayed ref
+ *	action.
+ *
+ * This will add an action item to the given bytenr and do sanity checks to make
+ * sure we haven't messed something up.  If we are making a new allocation and
+ * this block entry has history we will delete all previous actions as long as
+ * our sanity checks pass as they are no longer needed.
+ */
+int btrfs_ref_tree_mod(struct btrfs_root *root, u64 bytenr, u64 num_bytes,
+		       u64 parent, u64 ref_root, u64 owner, u64 offset,
+		       int action)
+{
+	struct btrfs_fs_info *fs_info = root->fs_info;
+	struct ref_entry *ref = NULL, *exist;
+	struct ref_action *ra = NULL;
+	struct block_entry *be = NULL;
+	struct root_entry *re = NULL;
+	int ret = 0;
+	bool metadata = owner < BTRFS_FIRST_FREE_OBJECTID;
+
+	if (!btrfs_test_opt(root->fs_info, REF_VERIFY))
+		return 0;
+
+	ref = kzalloc(sizeof(struct ref_entry), GFP_NOFS);
+	ra = kmalloc(sizeof(struct ref_action), GFP_NOFS);
+	if (!ra || !ref) {
+		kfree(ref);
+		kfree(ra);
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	if (parent) {
+		ref->parent = parent;
+	} else {
+		ref->root_objectid = ref_root;
+		ref->owner = owner;
+		ref->offset = offset;
+	}
+	ref->num_refs = (action == BTRFS_DROP_DELAYED_REF) ? -1 : 1;
+
+	memcpy(&ra->ref, ref, sizeof(struct ref_entry));
+	/*
+	 * Save the extra info from the delayed ref in the ref action to make it
+	 * easier to figure out what is happening.  The real ref's we add to the
+	 * ref tree need to reflect what we save on disk so it matches any
+	 * on-disk refs we pre-loaded.
+	 */
+	ra->ref.owner = owner;
+	ra->ref.offset = offset;
+	ra->ref.root_objectid = ref_root;
+	__save_stack_trace(ra);
+
+	INIT_LIST_HEAD(&ra->list);
+	ra->action = action;
+	ra->root = root->objectid;
+
+	/*
+	 * This is an allocation, preallocate the block_entry in case we haven't
+	 * used it before.
+	 */
+	ret = -EINVAL;
+	if (action == BTRFS_ADD_DELAYED_EXTENT) {
+		/*
+		 * For subvol_create we'll just pass in whatever the parent root
+		 * is and the new root objectid, so let's not treat the passed
+		 * in root as if it really has a ref for this bytenr.
+		 */
+		be = add_block_entry(root->fs_info, bytenr, num_bytes, ref_root);
+		if (IS_ERR(be)) {
+			kfree(ra);
+			ret = PTR_ERR(be);
+			goto out;
+		}
+		be->num_refs++;
+		if (metadata)
+			be->metadata = 1;
+
+		if (be->num_refs != 1) {
+			btrfs_err(fs_info,
+			"re-allocated a block that still has references to it!");
+			dump_block_entry(fs_info, be);
+			dump_ref_action(fs_info, ra);
+			goto out_unlock;
+		}
+
+		while (!list_empty(&be->actions)) {
+			struct ref_action *tmp;
+
+			tmp = list_first_entry(&be->actions, struct ref_action,
+					       list);
+			list_del(&tmp->list);
+			kfree(tmp);
+		}
+	} else {
+		struct root_entry *tmp;
+
+		if (!parent) {
+			re = kmalloc(sizeof(struct root_entry), GFP_NOFS);
+			if (!re) {
+				kfree(ref);
+				kfree(ra);
+				ret = -ENOMEM;
+				goto out;
+			}
+			/*
+			 * This is the root that is modifying us, so it's the
+			 * one we want to lookup below when we modify the
+			 * re->num_refs.
+			 */
+			ref_root = root->objectid;
+			re->root_objectid = root->objectid;
+			re->num_refs = 0;
+		}
+
+		spin_lock(&root->fs_info->ref_verify_lock);
+		be = lookup_block_entry(&root->fs_info->block_tree, bytenr);
+		if (!be) {
+			btrfs_err(fs_info,
+"trying to do action %d to bytenr %llu num_bytes %llu but there is no existing entry!",
+				  action, (unsigned long long)bytenr,
+				  (unsigned long long)num_bytes);
+			dump_ref_action(fs_info, ra);
+			kfree(ref);
+			kfree(ra);
+			goto out_unlock;
+		}
+
+		if (!parent) {
+			tmp = insert_root_entry(&be->roots, re);
+			if (tmp) {
+				kfree(re);
+				re = tmp;
+			}
+		}
+	}
+
+	exist = insert_ref_entry(&be->refs, ref);
+	if (exist) {
+		if (action == BTRFS_DROP_DELAYED_REF) {
+			if (exist->num_refs == 0) {
+				btrfs_err(fs_info,
+"dropping a ref for a existing root that doesn't have a ref on the block");
+				dump_block_entry(fs_info, be);
+				dump_ref_action(fs_info, ra);
+				kfree(ra);
+				goto out_unlock;
+			}
+			exist->num_refs--;
+			if (exist->num_refs == 0) {
+				rb_erase(&exist->node, &be->refs);
+				kfree(exist);
+			}
+		} else if (!be->metadata) {
+			exist->num_refs++;
+		} else {
+			btrfs_err(fs_info,
+"attempting to add another ref for an existing ref on a tree block");
+			dump_block_entry(fs_info, be);
+			dump_ref_action(fs_info, ra);
+			kfree(ra);
+			goto out_unlock;
+		}
+		kfree(ref);
+	} else {
+		if (action == BTRFS_DROP_DELAYED_REF) {
+			btrfs_err(fs_info,
+"dropping a ref for a root that doesn't have a ref on the block");
+			dump_block_entry(fs_info, be);
+			dump_ref_action(fs_info, ra);
+			kfree(ra);
+			goto out_unlock;
+		}
+	}
+
+	if (!parent && !re) {
+		re = lookup_root_entry(&be->roots, ref_root);
+		if (!re) {
+			/*
+			 * This shouldn't happen because we will add our re
+			 * above when we lookup the be with !parent, but just in
+			 * case catch this case so we don't panic because I
+			 * didn't thik of some other corner case.
+			 */
+			btrfs_err(fs_info, "failed to find root %llu for %llu",
+				  root->objectid, be->bytenr);
+			dump_block_entry(fs_info, be);
+			dump_ref_action(fs_info, ra);
+			kfree(ra);
+			goto out_unlock;
+		}
+	}
+	if (action == BTRFS_DROP_DELAYED_REF) {
+		if (re)
+			re->num_refs--;
+		be->num_refs--;
+	} else if (action == BTRFS_ADD_DELAYED_REF) {
+		be->num_refs++;
+		if (re)
+			re->num_refs++;
+	}
+	list_add_tail(&ra->list, &be->actions);
+	ret = 0;
+out_unlock:
+	spin_unlock(&root->fs_info->ref_verify_lock);
+out:
+	if (ret)
+		btrfs_clear_opt(fs_info->mount_opt, REF_VERIFY);
+	return ret;
+}
+
+/* Free up the ref cache */
+void btrfs_free_ref_cache(struct btrfs_fs_info *fs_info)
+{
+	struct block_entry *be;
+	struct rb_node *n;
+
+	if (!btrfs_test_opt(fs_info, REF_VERIFY))
+		return;
+
+	spin_lock(&fs_info->ref_verify_lock);
+	while ((n = rb_first(&fs_info->block_tree))) {
+		be = rb_entry(n, struct block_entry, node);
+		rb_erase(&be->node, &fs_info->block_tree);
+		free_block_entry(be);
+		cond_resched_lock(&fs_info->ref_verify_lock);
+	}
+	spin_unlock(&fs_info->ref_verify_lock);
+}
+
+void btrfs_free_ref_tree_range(struct btrfs_fs_info *fs_info, u64 start,
+			       u64 len)
+{
+	struct block_entry *be = NULL, *entry;
+	struct rb_node *n;
+
+	if (!btrfs_test_opt(fs_info, REF_VERIFY))
+		return;
+
+	spin_lock(&fs_info->ref_verify_lock);
+	n = fs_info->block_tree.rb_node;
+	while (n) {
+		entry = rb_entry(n, struct block_entry, node);
+		if (entry->bytenr < start) {
+			n = n->rb_right;
+		} else if (entry->bytenr > start) {
+			n = n->rb_left;
+		} else {
+			be = entry;
+			break;
+		}
+		/* We want to get as close to start as possible */
+		if (be == NULL ||
+		    (entry->bytenr < start && be->bytenr > start) ||
+		    (entry->bytenr < start && entry->bytenr > be->bytenr))
+			be = entry;
+	}
+
+	/*
+	 * Could have an empty block group, maybe have something to check for
+	 * this case to verify we were actually empty?
+	 */
+	if (!be) {
+		spin_unlock(&fs_info->ref_verify_lock);
+		return;
+	}
+
+	n = &be->node;
+	while (n) {
+		be = rb_entry(n, struct block_entry, node);
+		n = rb_next(n);
+		if (be->bytenr < start && be->bytenr + be->len > start) {
+			btrfs_err(fs_info,
+				"block entry overlaps a block group [%llu,%llu]!",
+				start, len);
+			dump_block_entry(fs_info, be);
+			continue;
+		}
+		if (be->bytenr < start)
+			continue;
+		if (be->bytenr >= start + len)
+			break;
+		if (be->bytenr + be->len > start + len) {
+			btrfs_err(fs_info,
+				"block entry overlaps a block group [%llu,%llu]!",
+				start, len);
+			dump_block_entry(fs_info, be);
+		}
+		rb_erase(&be->node, &fs_info->block_tree);
+		free_block_entry(be);
+	}
+	spin_unlock(&fs_info->ref_verify_lock);
+}
+
+/* Walk down all roots and build the ref tree, meant to be called at mount */
+int btrfs_build_ref_tree(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_path *path;
+	struct btrfs_root *root;
+	struct extent_buffer *eb;
+	u64 bytenr = 0, num_bytes = 0;
+	int ret, level;
+
+	if (!btrfs_test_opt(fs_info, REF_VERIFY))
+		return 0;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	eb = btrfs_read_lock_root_node(fs_info->extent_root);
+	btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
+	level = btrfs_header_level(eb);
+	path->nodes[level] = eb;
+	path->slots[level] = 0;
+	path->locks[level] = BTRFS_READ_LOCK_BLOCKING;
+
+	while (1) {
+		/*
+		 * We have to keep track of the bytenr/num_bytes we last hit
+		 * because we could have run out of space for an inline ref, and
+		 * would have had to added a ref key item which may appear on a
+		 * different leaf from the original extent item.
+		 */
+		ret = walk_down_tree(fs_info->extent_root, path, level,
+				     &bytenr, &num_bytes);
+		if (ret)
+			break;
+		ret = walk_up_tree(root, path, &level);
+		if (ret < 0)
+			break;
+		if (ret > 0) {
+			ret = 0;
+			break;
+		}
+	}
+	if (ret) {
+		btrfs_clear_opt(fs_info->mount_opt, REF_VERIFY);
+		btrfs_free_ref_cache(fs_info);
+	}
+	btrfs_free_path(path);
+	return ret;
+}
diff --git a/fs/btrfs/ref-verify.h b/fs/btrfs/ref-verify.h
new file mode 100644
index 000000000000..3bf02ce0e1e2
--- /dev/null
+++ b/fs/btrfs/ref-verify.h
@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2014 Facebook.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+#ifndef __REF_VERIFY__
+#define __REF_VERIFY__
+
+#ifdef CONFIG_BTRFS_FS_REF_VERIFY
+int btrfs_build_ref_tree(struct btrfs_fs_info *fs_info);
+void btrfs_free_ref_cache(struct btrfs_fs_info *fs_info);
+int btrfs_ref_tree_mod(struct btrfs_root *root, u64 bytenr, u64 num_bytes,
+		       u64 parent, u64 ref_root, u64 owner, u64 offset,
+		       int action);
+void btrfs_free_ref_tree_range(struct btrfs_fs_info *fs_info, u64 start,
+			       u64 len);
+
+static inline void btrfs_init_ref_verify(struct btrfs_fs_info *fs_info)
+{
+	spin_lock_init(&fs_info->ref_verify_lock);
+	fs_info->block_tree = RB_ROOT;
+}
+#else
+static inline int btrfs_build_ref_tree(struct btrfs_fs_info *fs_info)
+{
+	return 0;
+}
+
+static inline void btrfs_free_ref_cache(struct btrfs_fs_info *fs_info)
+{
+}
+
+static inline int btrfs_ref_tree_mod(struct btrfs_root *root, u64 bytenr,
+				     u64 num_bytes, u64 parent, u64 ref_root,
+				     u64 owner, u64 offset, int action)
+{
+	return 0;
+}
+
+static inline void btrfs_free_ref_tree_range(struct btrfs_fs_info *fs_info,
+					     u64 start, u64 len)
+{
+}
+
+static inline void btrfs_init_ref_verify(struct btrfs_fs_info *fs_info)
+{
+}
+
+#endif /* CONFIG_BTRFS_FS_REF_VERIFY */
+#endif /* _REF_VERIFY__ */