diff --git a/fs/btrfs/Kconfig b/fs/btrfs/Kconfig
index 5f583c8..4b3ac45 100644
--- a/fs/btrfs/Kconfig
+++ b/fs/btrfs/Kconfig
@@ -53,3 +53,14 @@ config BTRFS_FS_CHECK_INTEGRITY
 	  In most cases, unless you are a btrfs developer who needs
 	  to verify the integrity of (super)-block write requests
 	  during the run of a regression test, say N
+
+config BTRFS_FS_RUN_SANITY_TESTS
+	bool "Btrfs will run sanity tests upon loading"
+	depends on BTRFS_FS
+	help
+	  This will run some basic sanity tests on the free space cache
+	  code to make sure it is acting as it should.  These are mostly
+	  regression tests and are only really interesting to btrfs devlopers.
+
+	  If unsure, say N.
+
diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 1f84fc0..fcde73d 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -2967,3 +2967,522 @@ int btrfs_write_out_ino_cache(struct btrfs_root *root,
 	iput(inode);
 	return ret;
 }
+
+#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
+static struct btrfs_block_group_cache *init_test_block_group(void)
+{
+	struct btrfs_block_group_cache *cache;
+
+	cache = kzalloc(sizeof(*cache), GFP_NOFS);
+	if (!cache)
+		return NULL;
+	cache->free_space_ctl = kzalloc(sizeof(*cache->free_space_ctl),
+					GFP_NOFS);
+	if (!cache->free_space_ctl) {
+		kfree(cache);
+		return NULL;
+	}
+
+	cache->key.objectid = 0;
+	cache->key.offset = 1024 * 1024 * 1024;
+	cache->key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
+	cache->sectorsize = 4096;
+
+	spin_lock_init(&cache->lock);
+	INIT_LIST_HEAD(&cache->list);
+	INIT_LIST_HEAD(&cache->cluster_list);
+	INIT_LIST_HEAD(&cache->new_bg_list);
+
+	btrfs_init_free_space_ctl(cache);
+
+	return cache;
+}
+
+/*
+ * Checks to see if the given range is in the free space cache.  This is really
+ * just used to check the absence of space, so if there is free space in the
+ * range at all we will return 1.
+ */
+static int check_exists(struct btrfs_block_group_cache *cache, u64 offset,
+			u64 bytes)
+{
+	struct btrfs_free_space_ctl *ctl = cache->free_space_ctl;
+	struct btrfs_free_space *info;
+	int ret = 0;
+
+	spin_lock(&ctl->tree_lock);
+	info = tree_search_offset(ctl, offset, 0, 0);
+	if (!info) {
+		info = tree_search_offset(ctl, offset_to_bitmap(ctl, offset),
+					  1, 0);
+		if (!info)
+			goto out;
+	}
+
+have_info:
+	if (info->bitmap) {
+		u64 bit_off, bit_bytes;
+		struct rb_node *n;
+		struct btrfs_free_space *tmp;
+
+		bit_off = offset;
+		bit_bytes = ctl->unit;
+		ret = search_bitmap(ctl, info, &bit_off, &bit_bytes);
+		if (!ret) {
+			if (bit_off == offset) {
+				ret = 1;
+				goto out;
+			} else if (bit_off > offset &&
+				   offset + bytes > bit_off) {
+				ret = 1;
+				goto out;
+			}
+		}
+
+		n = rb_prev(&info->offset_index);
+		while (n) {
+			tmp = rb_entry(n, struct btrfs_free_space,
+				       offset_index);
+			if (tmp->offset + tmp->bytes < offset)
+				break;
+			if (offset + bytes < tmp->offset) {
+				n = rb_prev(&info->offset_index);
+				continue;
+			}
+			info = tmp;
+			goto have_info;
+		}
+
+		n = rb_next(&info->offset_index);
+		while (n) {
+			tmp = rb_entry(n, struct btrfs_free_space,
+				       offset_index);
+			if (offset + bytes < tmp->offset)
+				break;
+			if (tmp->offset + tmp->bytes < offset) {
+				n = rb_next(&info->offset_index);
+				continue;
+			}
+			info = tmp;
+			goto have_info;
+		}
+
+		goto out;
+	}
+
+	if (info->offset == offset) {
+		ret = 1;
+		goto out;
+	}
+
+	if (offset > info->offset && offset < info->offset + info->bytes)
+		ret = 1;
+out:
+	spin_unlock(&ctl->tree_lock);
+	return ret;
+}
+
+/*
+ * Use this if you need to make a bitmap or extent entry specifically, it
+ * doesn't do any of the merging that add_free_space does, this acts a lot like
+ * how the free space cache loading stuff works, so you can get really weird
+ * configurations.
+ */
+static int add_free_space_entry(struct btrfs_block_group_cache *cache,
+				u64 offset, u64 bytes, bool bitmap)
+{
+	struct btrfs_free_space_ctl *ctl = cache->free_space_ctl;
+	struct btrfs_free_space *info = NULL, *bitmap_info;
+	void *map = NULL;
+	u64 bytes_added;
+	int ret;
+
+again:
+	if (!info) {
+		info = kmem_cache_zalloc(btrfs_free_space_cachep, GFP_NOFS);
+		if (!info)
+			return -ENOMEM;
+	}
+
+	if (!bitmap) {
+		spin_lock(&ctl->tree_lock);
+		info->offset = offset;
+		info->bytes = bytes;
+		ret = link_free_space(ctl, info);
+		spin_unlock(&ctl->tree_lock);
+		if (ret)
+			kmem_cache_free(btrfs_free_space_cachep, info);
+		return ret;
+	}
+
+	if (!map) {
+		map = kzalloc(PAGE_CACHE_SIZE, GFP_NOFS);
+		if (!map) {
+			kmem_cache_free(btrfs_free_space_cachep, info);
+			return -ENOMEM;
+		}
+	}
+
+	spin_lock(&ctl->tree_lock);
+	bitmap_info = tree_search_offset(ctl, offset_to_bitmap(ctl, offset),
+					 1, 0);
+	if (!bitmap_info) {
+		info->bitmap = map;
+		map = NULL;
+		add_new_bitmap(ctl, info, offset);
+		bitmap_info = info;
+	}
+
+	bytes_added = add_bytes_to_bitmap(ctl, bitmap_info, offset, bytes);
+	bytes -= bytes_added;
+	offset += bytes_added;
+	spin_unlock(&ctl->tree_lock);
+
+	if (bytes)
+		goto again;
+
+	if (map)
+		kfree(map);
+	return 0;
+}
+
+/*
+ * This test just does basic sanity checking, making sure we can add an exten
+ * entry and remove space from either end and the middle, and make sure we can
+ * remove space that covers adjacent extent entries.
+ */
+static int test_extents(struct btrfs_block_group_cache *cache)
+{
+	int ret = 0;
+
+	printk(KERN_ERR "Running extent only tests\n");
+
+	/* First just make sure we can remove an entire entry */
+	ret = btrfs_add_free_space(cache, 0, 4 * 1024 * 1024);
+	if (ret) {
+		printk(KERN_ERR "Error adding initial extents %d\n", ret);
+		return ret;
+	}
+
+	ret = btrfs_remove_free_space(cache, 0, 4 * 1024 * 1024);
+	if (ret) {
+		printk(KERN_ERR "Error removing extent %d\n", ret);
+		return ret;
+	}
+
+	if (check_exists(cache, 0, 4 * 1024 * 1024)) {
+		printk(KERN_ERR "Full remove left some lingering space\n");
+		return -1;
+	}
+
+	/* Ok edge and middle cases now */
+	ret = btrfs_add_free_space(cache, 0, 4 * 1024 * 1024);
+	if (ret) {
+		printk(KERN_ERR "Error adding half extent %d\n", ret);
+		return ret;
+	}
+
+	ret = btrfs_remove_free_space(cache, 3 * 1024 * 1024, 1 * 1024 * 1024);
+	if (ret) {
+		printk(KERN_ERR "Error removing tail end %d\n", ret);
+		return ret;
+	}
+
+	ret = btrfs_remove_free_space(cache, 0, 1 * 1024 * 1024);
+	if (ret) {
+		printk(KERN_ERR "Error removing front end %d\n", ret);
+		return ret;
+	}
+
+	ret = btrfs_remove_free_space(cache, 2 * 1024 * 1024, 4096);
+	if (ret) {
+		printk(KERN_ERR "Error removing middle peice %d\n", ret);
+		return ret;
+	}
+
+	if (check_exists(cache, 0, 1 * 1024 * 1024)) {
+		printk(KERN_ERR "Still have space at the front\n");
+		return -1;
+	}
+
+	if (check_exists(cache, 2 * 1024 * 1024, 4096)) {
+		printk(KERN_ERR "Still have space in the middle\n");
+		return -1;
+	}
+
+	if (check_exists(cache, 3 * 1024 * 1024, 1 * 1024 * 1024)) {
+		printk(KERN_ERR "Still have space at the end\n");
+		return -1;
+	}
+
+	/* Cleanup */
+	__btrfs_remove_free_space_cache(cache->free_space_ctl);
+
+	return 0;
+}
+
+static int test_bitmaps(struct btrfs_block_group_cache *cache)
+{
+	u64 next_bitmap_offset;
+	int ret;
+
+	printk(KERN_ERR "Running bitmap only tests\n");
+
+	ret = add_free_space_entry(cache, 0, 4 * 1024 * 1024, 1);
+	if (ret) {
+		printk(KERN_ERR "Couldn't create a bitmap entry %d\n", ret);
+		return ret;
+	}
+
+	ret = btrfs_remove_free_space(cache, 0, 4 * 1024 * 1024);
+	if (ret) {
+		printk(KERN_ERR "Error removing bitmap full range %d\n", ret);
+		return ret;
+	}
+
+	if (check_exists(cache, 0, 4 * 1024 * 1024)) {
+		printk(KERN_ERR "Left some space in bitmap\n");
+		return -1;
+	}
+
+	ret = add_free_space_entry(cache, 0, 4 * 1024 * 1024, 1);
+	if (ret) {
+		printk(KERN_ERR "Couldn't add to our bitmap entry %d\n", ret);
+		return ret;
+	}
+
+	ret = btrfs_remove_free_space(cache, 1 * 1024 * 1024, 2 * 1024 * 1024);
+	if (ret) {
+		printk(KERN_ERR "Couldn't remove middle chunk %d\n", ret);
+		return ret;
+	}
+
+	/*
+	 * The first bitmap we have starts at offset 0 so the next one is just
+	 * at the end of the first bitmap.
+	 */
+	next_bitmap_offset = (u64)(BITS_PER_BITMAP * 4096);
+
+	/* Test a bit straddling two bitmaps */
+	ret = add_free_space_entry(cache, next_bitmap_offset -
+				   (2 * 1024 * 1024), 4 * 1024 * 1024, 1);
+	if (ret) {
+		printk(KERN_ERR "Couldn't add space that straddles two bitmaps"
+		       " %d\n", ret);
+		return ret;
+	}
+
+	ret = btrfs_remove_free_space(cache, next_bitmap_offset -
+				      (1 * 1024 * 1024), 2 * 1024 * 1024);
+	if (ret) {
+		printk(KERN_ERR "Couldn't remove overlapping space %d\n", ret);
+		return ret;
+	}
+
+	if (check_exists(cache, next_bitmap_offset - (1 * 1024 * 1024),
+			 2 * 1024 * 1024)) {
+		printk(KERN_ERR "Left some space when removing overlapping\n");
+		return -1;
+	}
+
+	__btrfs_remove_free_space_cache(cache->free_space_ctl);
+
+	return 0;
+}
+
+/* This is the high grade jackassery */
+static int test_bitmaps_and_extents(struct btrfs_block_group_cache *cache)
+{
+	u64 bitmap_offset = (u64)(BITS_PER_BITMAP * 4096);
+	int ret;
+
+	printk(KERN_ERR "Running bitmap and extent tests\n");
+
+	/*
+	 * First let's do something simple, an extent at the same offset as the
+	 * bitmap, but the free space completely in the extent and then
+	 * completely in the bitmap.
+	 */
+	ret = add_free_space_entry(cache, 4 * 1024 * 1024, 1 * 1024 * 1024, 1);
+	if (ret) {
+		printk(KERN_ERR "Couldn't create bitmap entry %d\n", ret);
+		return ret;
+	}
+
+	ret = add_free_space_entry(cache, 0, 1 * 1024 * 1024, 0);
+	if (ret) {
+		printk(KERN_ERR "Couldn't add extent entry %d\n", ret);
+		return ret;
+	}
+
+	ret = btrfs_remove_free_space(cache, 0, 1 * 1024 * 1024);
+	if (ret) {
+		printk(KERN_ERR "Couldn't remove extent entry %d\n", ret);
+		return ret;
+	}
+
+	if (check_exists(cache, 0, 1 * 1024 * 1024)) {
+		printk(KERN_ERR "Left remnants after our remove\n");
+		return -1;
+	}
+
+	/* Now to add back the extent entry and remove from the bitmap */
+	ret = add_free_space_entry(cache, 0, 1 * 1024 * 1024, 0);
+	if (ret) {
+		printk(KERN_ERR "Couldn't re-add extent entry %d\n", ret);
+		return ret;
+	}
+
+	ret = btrfs_remove_free_space(cache, 4 * 1024 * 1024, 1 * 1024 * 1024);
+	if (ret) {
+		printk(KERN_ERR "Couldn't remove from bitmap %d\n", ret);
+		return ret;
+	}
+
+	if (check_exists(cache, 4 * 1024 * 1024, 1 * 1024 * 1024)) {
+		printk(KERN_ERR "Left remnants in the bitmap\n");
+		return -1;
+	}
+
+	/*
+	 * Ok so a little more evil, extent entry and bitmap at the same offset,
+	 * removing an overlapping chunk.
+	 */
+	ret = add_free_space_entry(cache, 1 * 1024 * 1024, 4 * 1024 * 1024, 1);
+	if (ret) {
+		printk(KERN_ERR "Couldn't add to a bitmap %d\n", ret);
+		return ret;
+	}
+
+	ret = btrfs_remove_free_space(cache, 512 * 1024, 3 * 1024 * 1024);
+	if (ret) {
+		printk(KERN_ERR "Couldn't remove overlapping space %d\n", ret);
+		return ret;
+	}
+
+	if (check_exists(cache, 512 * 1024, 3 * 1024 * 1024)) {
+		printk(KERN_ERR "Left over peices after removing "
+		       "overlapping\n");
+		return -1;
+	}
+
+	__btrfs_remove_free_space_cache(cache->free_space_ctl);
+
+	/* Now with the extent entry offset into the bitmap */
+	ret = add_free_space_entry(cache, 4 * 1024 * 1024, 4 * 1024 * 1024, 1);
+	if (ret) {
+		printk(KERN_ERR "Couldn't add space to the bitmap %d\n", ret);
+		return ret;
+	}
+
+	ret = add_free_space_entry(cache, 2 * 1024 * 1024, 2 * 1024 * 1024, 0);
+	if (ret) {
+		printk(KERN_ERR "Couldn't add extent to the cache %d\n", ret);
+		return ret;
+	}
+
+	ret = btrfs_remove_free_space(cache, 3 * 1024 * 1024, 4 * 1024 * 1024);
+	if (ret) {
+		printk(KERN_ERR "Problem removing overlapping space %d\n", ret);
+		return ret;
+	}
+
+	if (check_exists(cache, 3 * 1024 * 1024, 4 * 1024 * 1024)) {
+		printk(KERN_ERR "Left something behind when removing space");
+		return -1;
+	}
+
+	/*
+	 * This has blown up in the past, the extent entry starts before the
+	 * bitmap entry, but we're trying to remove an offset that falls
+	 * completely within the bitmap range and is in both the extent entry
+	 * and the bitmap entry, looks like this
+	 *
+	 *   [ extent ]
+	 *      [ bitmap ]
+	 *        [ del ]
+	 */
+	__btrfs_remove_free_space_cache(cache->free_space_ctl);
+	ret = add_free_space_entry(cache, bitmap_offset + 4 * 1024 * 1024,
+				   4 * 1024 * 1024, 1);
+	if (ret) {
+		printk(KERN_ERR "Couldn't add bitmap %d\n", ret);
+		return ret;
+	}
+
+	ret = add_free_space_entry(cache, bitmap_offset - 1 * 1024 * 1024,
+				   5 * 1024 * 1024, 0);
+	if (ret) {
+		printk(KERN_ERR "Couldn't add extent entry %d\n", ret);
+		return ret;
+	}
+
+	ret = btrfs_remove_free_space(cache, bitmap_offset + 1 * 1024 * 1024,
+				      5 * 1024 * 1024);
+	if (ret) {
+		printk(KERN_ERR "Failed to free our space %d\n", ret);
+		return ret;
+	}
+
+	if (check_exists(cache, bitmap_offset + 1 * 1024 * 1024,
+			 5 * 1024 * 1024)) {
+		printk(KERN_ERR "Left stuff over\n");
+		return -1;
+	}
+
+	__btrfs_remove_free_space_cache(cache->free_space_ctl);
+
+	/*
+	 * This blew up before, we have part of the free space in a bitmap and
+	 * then the entirety of the rest of the space in an extent.  This used
+	 * to return -EAGAIN back from btrfs_remove_extent, make sure this
+	 * doesn't happen.
+	 */
+	ret = add_free_space_entry(cache, 1 * 1024 * 1024, 2 * 1024 * 1024, 1);
+	if (ret) {
+		printk(KERN_ERR "Couldn't add bitmap entry %d\n", ret);
+		return ret;
+	}
+
+	ret = add_free_space_entry(cache, 3 * 1024 * 1024, 1 * 1024 * 1024, 0);
+	if (ret) {
+		printk(KERN_ERR "Couldn't add extent entry %d\n", ret);
+		return ret;
+	}
+
+	ret = btrfs_remove_free_space(cache, 1 * 1024 * 1024, 3 * 1024 * 1024);
+	if (ret) {
+		printk(KERN_ERR "Error removing bitmap and extent "
+		       "overlapping %d\n", ret);
+		return ret;
+	}
+
+	__btrfs_remove_free_space_cache(cache->free_space_ctl);
+	return 0;
+}
+
+void btrfs_test_free_space_cache()
+{
+	struct btrfs_block_group_cache *cache;
+
+	printk(KERN_ERR "Running btrfs free space cache tests\n");
+
+	cache = init_test_block_group();
+	if (!cache) {
+		printk(KERN_ERR "Couldn't run the tests\n");
+		return;
+	}
+
+	if (test_extents(cache))
+		goto out;
+	if (test_bitmaps(cache))
+		goto out;
+	if (test_bitmaps_and_extents(cache))
+		goto out;
+out:
+	__btrfs_remove_free_space_cache(cache->free_space_ctl);
+	kfree(cache->free_space_ctl);
+	kfree(cache);
+	printk(KERN_ERR "Free space cache tests finished\n");
+}
+#endif /* CONFIG_BTRFS_FS_RUN_SANITY_TESTS */
diff --git a/fs/btrfs/free-space-cache.h b/fs/btrfs/free-space-cache.h
index 8f2613f..4dc17d8 100644
--- a/fs/btrfs/free-space-cache.h
+++ b/fs/btrfs/free-space-cache.h
@@ -110,4 +110,9 @@ int btrfs_return_cluster_to_free_space(
 			       struct btrfs_free_cluster *cluster);
 int btrfs_trim_block_group(struct btrfs_block_group_cache *block_group,
 			   u64 *trimmed, u64 start, u64 end, u64 minlen);
+
+#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
+void btrfs_test_free_space_cache(void);
+#endif
+
 #endif
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 68a29a1..096316f 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -56,6 +56,7 @@
 #include "compression.h"
 #include "rcu-string.h"
 #include "dev-replace.h"
+#include "free-space-cache.h"
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/btrfs.h>
@@ -1738,6 +1739,10 @@ static int __init init_btrfs_fs(void)
 
 	btrfs_init_lockdep();
 
+#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
+	btrfs_test_free_space_cache();
+#endif
+
 	printk(KERN_INFO "%s loaded\n", BTRFS_BUILD_VERSION);
 	return 0;
 
