Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 4545 insertions, 0 deletions

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
new file mode 100644
index 0000000000..5a97db9888
--- /dev/null
+++ b/fs/btrfs/block-group.c
@@ -0,0 +1,4545 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/sizes.h>
+#include <linux/list_sort.h>
+#include "misc.h"
+#include "ctree.h"
+#include "block-group.h"
+#include "space-info.h"
+#include "disk-io.h"
+#include "free-space-cache.h"
+#include "free-space-tree.h"
+#include "volumes.h"
+#include "transaction.h"
+#include "ref-verify.h"
+#include "sysfs.h"
+#include "tree-log.h"
+#include "delalloc-space.h"
+#include "discard.h"
+#include "raid56.h"
+#include "zoned.h"
+#include "fs.h"
+#include "accessors.h"
+#include "extent-tree.h"
+
+#ifdef CONFIG_BTRFS_DEBUG
+int btrfs_should_fragment_free_space(struct btrfs_block_group *block_group)
+{
+	struct btrfs_fs_info *fs_info = block_group->fs_info;
+
+	return (btrfs_test_opt(fs_info, FRAGMENT_METADATA) &&
+		block_group->flags & BTRFS_BLOCK_GROUP_METADATA) ||
+	       (btrfs_test_opt(fs_info, FRAGMENT_DATA) &&
+		block_group->flags &  BTRFS_BLOCK_GROUP_DATA);
+}
+#endif
+
+/*
+ * Return target flags in extended format or 0 if restripe for this chunk_type
+ * is not in progress
+ *
+ * Should be called with balance_lock held
+ */
+static u64 get_restripe_target(struct btrfs_fs_info *fs_info, u64 flags)
+{
+	struct btrfs_balance_control *bctl = fs_info->balance_ctl;
+	u64 target = 0;
+
+	if (!bctl)
+		return 0;
+
+	if (flags & BTRFS_BLOCK_GROUP_DATA &&
+	    bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT) {
+		target = BTRFS_BLOCK_GROUP_DATA | bctl->data.target;
+	} else if (flags & BTRFS_BLOCK_GROUP_SYSTEM &&
+		   bctl->sys.flags & BTRFS_BALANCE_ARGS_CONVERT) {
+		target = BTRFS_BLOCK_GROUP_SYSTEM | bctl->sys.target;
+	} else if (flags & BTRFS_BLOCK_GROUP_METADATA &&
+		   bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT) {
+		target = BTRFS_BLOCK_GROUP_METADATA | bctl->meta.target;
+	}
+
+	return target;
+}
+
+/*
+ * @flags: available profiles in extended format (see ctree.h)
+ *
+ * Return reduced profile in chunk format.  If profile changing is in progress
+ * (either running or paused) picks the target profile (if it's already
+ * available), otherwise falls back to plain reducing.
+ */
+static u64 btrfs_reduce_alloc_profile(struct btrfs_fs_info *fs_info, u64 flags)
+{
+	u64 num_devices = fs_info->fs_devices->rw_devices;
+	u64 target;
+	u64 raid_type;
+	u64 allowed = 0;
+
+	/*
+	 * See if restripe for this chunk_type is in progress, if so try to
+	 * reduce to the target profile
+	 */
+	spin_lock(&fs_info->balance_lock);
+	target = get_restripe_target(fs_info, flags);
+	if (target) {
+		spin_unlock(&fs_info->balance_lock);
+		return extended_to_chunk(target);
+	}
+	spin_unlock(&fs_info->balance_lock);
+
+	/* First, mask out the RAID levels which aren't possible */
+	for (raid_type = 0; raid_type < BTRFS_NR_RAID_TYPES; raid_type++) {
+		if (num_devices >= btrfs_raid_array[raid_type].devs_min)
+			allowed |= btrfs_raid_array[raid_type].bg_flag;
+	}
+	allowed &= flags;
+
+	/* Select the highest-redundancy RAID level. */
+	if (allowed & BTRFS_BLOCK_GROUP_RAID1C4)
+		allowed = BTRFS_BLOCK_GROUP_RAID1C4;
+	else if (allowed & BTRFS_BLOCK_GROUP_RAID6)
+		allowed = BTRFS_BLOCK_GROUP_RAID6;
+	else if (allowed & BTRFS_BLOCK_GROUP_RAID1C3)
+		allowed = BTRFS_BLOCK_GROUP_RAID1C3;
+	else if (allowed & BTRFS_BLOCK_GROUP_RAID5)
+		allowed = BTRFS_BLOCK_GROUP_RAID5;
+	else if (allowed & BTRFS_BLOCK_GROUP_RAID10)
+		allowed = BTRFS_BLOCK_GROUP_RAID10;
+	else if (allowed & BTRFS_BLOCK_GROUP_RAID1)
+		allowed = BTRFS_BLOCK_GROUP_RAID1;
+	else if (allowed & BTRFS_BLOCK_GROUP_DUP)
+		allowed = BTRFS_BLOCK_GROUP_DUP;
+	else if (allowed & BTRFS_BLOCK_GROUP_RAID0)
+		allowed = BTRFS_BLOCK_GROUP_RAID0;
+
+	flags &= ~BTRFS_BLOCK_GROUP_PROFILE_MASK;
+
+	return extended_to_chunk(flags | allowed);
+}
+
+u64 btrfs_get_alloc_profile(struct btrfs_fs_info *fs_info, u64 orig_flags)
+{
+	unsigned seq;
+	u64 flags;
+
+	do {
+		flags = orig_flags;
+		seq = read_seqbegin(&fs_info->profiles_lock);
+
+		if (flags & BTRFS_BLOCK_GROUP_DATA)
+			flags |= fs_info->avail_data_alloc_bits;
+		else if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
+			flags |= fs_info->avail_system_alloc_bits;
+		else if (flags & BTRFS_BLOCK_GROUP_METADATA)
+			flags |= fs_info->avail_metadata_alloc_bits;
+	} while (read_seqretry(&fs_info->profiles_lock, seq));
+
+	return btrfs_reduce_alloc_profile(fs_info, flags);
+}
+
+void btrfs_get_block_group(struct btrfs_block_group *cache)
+{
+	refcount_inc(&cache->refs);
+}
+
+void btrfs_put_block_group(struct btrfs_block_group *cache)
+{
+	if (refcount_dec_and_test(&cache->refs)) {
+		WARN_ON(cache->pinned > 0);
+		/*
+		 * If there was a failure to cleanup a log tree, very likely due
+		 * to an IO failure on a writeback attempt of one or more of its
+		 * extent buffers, we could not do proper (and cheap) unaccounting
+		 * of their reserved space, so don't warn on reserved > 0 in that
+		 * case.
+		 */
+		if (!(cache->flags & BTRFS_BLOCK_GROUP_METADATA) ||
+		    !BTRFS_FS_LOG_CLEANUP_ERROR(cache->fs_info))
+			WARN_ON(cache->reserved > 0);
+
+		/*
+		 * A block_group shouldn't be on the discard_list anymore.
+		 * Remove the block_group from the discard_list to prevent us
+		 * from causing a panic due to NULL pointer dereference.
+		 */
+		if (WARN_ON(!list_empty(&cache->discard_list)))
+			btrfs_discard_cancel_work(&cache->fs_info->discard_ctl,
+						  cache);
+
+		kfree(cache->free_space_ctl);
+		kfree(cache->physical_map);
+		kfree(cache);
+	}
+}
+
+/*
+ * This adds the block group to the fs_info rb tree for the block group cache
+ */
+static int btrfs_add_block_group_cache(struct btrfs_fs_info *info,
+				       struct btrfs_block_group *block_group)
+{
+	struct rb_node **p;
+	struct rb_node *parent = NULL;
+	struct btrfs_block_group *cache;
+	bool leftmost = true;
+
+	ASSERT(block_group->length != 0);
+
+	write_lock(&info->block_group_cache_lock);
+	p = &info->block_group_cache_tree.rb_root.rb_node;
+
+	while (*p) {
+		parent = *p;
+		cache = rb_entry(parent, struct btrfs_block_group, cache_node);
+		if (block_group->start < cache->start) {
+			p = &(*p)->rb_left;
+		} else if (block_group->start > cache->start) {
+			p = &(*p)->rb_right;
+			leftmost = false;
+		} else {
+			write_unlock(&info->block_group_cache_lock);
+			return -EEXIST;
+		}
+	}
+
+	rb_link_node(&block_group->cache_node, parent, p);
+	rb_insert_color_cached(&block_group->cache_node,
+			       &info->block_group_cache_tree, leftmost);
+
+	write_unlock(&info->block_group_cache_lock);
+
+	return 0;
+}
+
+/*
+ * This will return the block group at or after bytenr if contains is 0, else
+ * it will return the block group that contains the bytenr
+ */
+static struct btrfs_block_group *block_group_cache_tree_search(
+		struct btrfs_fs_info *info, u64 bytenr, int contains)
+{
+	struct btrfs_block_group *cache, *ret = NULL;
+	struct rb_node *n;
+	u64 end, start;
+
+	read_lock(&info->block_group_cache_lock);
+	n = info->block_group_cache_tree.rb_root.rb_node;
+
+	while (n) {
+		cache = rb_entry(n, struct btrfs_block_group, cache_node);
+		end = cache->start + cache->length - 1;
+		start = cache->start;
+
+		if (bytenr < start) {
+			if (!contains && (!ret || start < ret->start))
+				ret = cache;
+			n = n->rb_left;
+		} else if (bytenr > start) {
+			if (contains && bytenr <= end) {
+				ret = cache;
+				break;
+			}
+			n = n->rb_right;
+		} else {
+			ret = cache;
+			break;
+		}
+	}
+	if (ret)
+		btrfs_get_block_group(ret);
+	read_unlock(&info->block_group_cache_lock);
+
+	return ret;
+}
+
+/*
+ * Return the block group that starts at or after bytenr
+ */
+struct btrfs_block_group *btrfs_lookup_first_block_group(
+		struct btrfs_fs_info *info, u64 bytenr)
+{
+	return block_group_cache_tree_search(info, bytenr, 0);
+}
+
+/*
+ * Return the block group that contains the given bytenr
+ */
+struct btrfs_block_group *btrfs_lookup_block_group(
+		struct btrfs_fs_info *info, u64 bytenr)
+{
+	return block_group_cache_tree_search(info, bytenr, 1);
+}
+
+struct btrfs_block_group *btrfs_next_block_group(
+		struct btrfs_block_group *cache)
+{
+	struct btrfs_fs_info *fs_info = cache->fs_info;
+	struct rb_node *node;
+
+	read_lock(&fs_info->block_group_cache_lock);
+
+	/* If our block group was removed, we need a full search. */
+	if (RB_EMPTY_NODE(&cache->cache_node)) {
+		const u64 next_bytenr = cache->start + cache->length;
+
+		read_unlock(&fs_info->block_group_cache_lock);
+		btrfs_put_block_group(cache);
+		return btrfs_lookup_first_block_group(fs_info, next_bytenr);
+	}
+	node = rb_next(&cache->cache_node);
+	btrfs_put_block_group(cache);
+	if (node) {
+		cache = rb_entry(node, struct btrfs_block_group, cache_node);
+		btrfs_get_block_group(cache);
+	} else
+		cache = NULL;
+	read_unlock(&fs_info->block_group_cache_lock);
+	return cache;
+}
+
+/*
+ * Check if we can do a NOCOW write for a given extent.
+ *
+ * @fs_info:       The filesystem information object.
+ * @bytenr:        Logical start address of the extent.
+ *
+ * Check if we can do a NOCOW write for the given extent, and increments the
+ * number of NOCOW writers in the block group that contains the extent, as long
+ * as the block group exists and it's currently not in read-only mode.
+ *
+ * Returns: A non-NULL block group pointer if we can do a NOCOW write, the caller
+ *          is responsible for calling btrfs_dec_nocow_writers() later.
+ *
+ *          Or NULL if we can not do a NOCOW write
+ */
+struct btrfs_block_group *btrfs_inc_nocow_writers(struct btrfs_fs_info *fs_info,
+						  u64 bytenr)
+{
+	struct btrfs_block_group *bg;
+	bool can_nocow = true;
+
+	bg = btrfs_lookup_block_group(fs_info, bytenr);
+	if (!bg)
+		return NULL;
+
+	spin_lock(&bg->lock);
+	if (bg->ro)
+		can_nocow = false;
+	else
+		atomic_inc(&bg->nocow_writers);
+	spin_unlock(&bg->lock);
+
+	if (!can_nocow) {
+		btrfs_put_block_group(bg);
+		return NULL;
+	}
+
+	/* No put on block group, done by btrfs_dec_nocow_writers(). */
+	return bg;
+}
+
+/*
+ * Decrement the number of NOCOW writers in a block group.
+ *
+ * This is meant to be called after a previous call to btrfs_inc_nocow_writers(),
+ * and on the block group returned by that call. Typically this is called after
+ * creating an ordered extent for a NOCOW write, to prevent races with scrub and
+ * relocation.
+ *
+ * After this call, the caller should not use the block group anymore. It it wants
+ * to use it, then it should get a reference on it before calling this function.
+ */
+void btrfs_dec_nocow_writers(struct btrfs_block_group *bg)
+{
+	if (atomic_dec_and_test(&bg->nocow_writers))
+		wake_up_var(&bg->nocow_writers);
+
+	/* For the lookup done by a previous call to btrfs_inc_nocow_writers(). */
+	btrfs_put_block_group(bg);
+}
+
+void btrfs_wait_nocow_writers(struct btrfs_block_group *bg)
+{
+	wait_var_event(&bg->nocow_writers, !atomic_read(&bg->nocow_writers));
+}
+
+void btrfs_dec_block_group_reservations(struct btrfs_fs_info *fs_info,
+					const u64 start)
+{
+	struct btrfs_block_group *bg;
+
+	bg = btrfs_lookup_block_group(fs_info, start);
+	ASSERT(bg);
+	if (atomic_dec_and_test(&bg->reservations))
+		wake_up_var(&bg->reservations);
+	btrfs_put_block_group(bg);
+}
+
+void btrfs_wait_block_group_reservations(struct btrfs_block_group *bg)
+{
+	struct btrfs_space_info *space_info = bg->space_info;
+
+	ASSERT(bg->ro);
+
+	if (!(bg->flags & BTRFS_BLOCK_GROUP_DATA))
+		return;
+
+	/*
+	 * Our block group is read only but before we set it to read only,
+	 * some task might have had allocated an extent from it already, but it
+	 * has not yet created a respective ordered extent (and added it to a
+	 * root's list of ordered extents).
+	 * Therefore wait for any task currently allocating extents, since the
+	 * block group's reservations counter is incremented while a read lock
+	 * on the groups' semaphore is held and decremented after releasing
+	 * the read access on that semaphore and creating the ordered extent.
+	 */
+	down_write(&space_info->groups_sem);
+	up_write(&space_info->groups_sem);
+
+	wait_var_event(&bg->reservations, !atomic_read(&bg->reservations));
+}
+
+struct btrfs_caching_control *btrfs_get_caching_control(
+		struct btrfs_block_group *cache)
+{
+	struct btrfs_caching_control *ctl;
+
+	spin_lock(&cache->lock);
+	if (!cache->caching_ctl) {
+		spin_unlock(&cache->lock);
+		return NULL;
+	}
+
+	ctl = cache->caching_ctl;
+	refcount_inc(&ctl->count);
+	spin_unlock(&cache->lock);
+	return ctl;
+}
+
+void btrfs_put_caching_control(struct btrfs_caching_control *ctl)
+{
+	if (refcount_dec_and_test(&ctl->count))
+		kfree(ctl);
+}
+
+/*
+ * When we wait for progress in the block group caching, its because our
+ * allocation attempt failed at least once.  So, we must sleep and let some
+ * progress happen before we try again.
+ *
+ * This function will sleep at least once waiting for new free space to show
+ * up, and then it will check the block group free space numbers for our min
+ * num_bytes.  Another option is to have it go ahead and look in the rbtree for
+ * a free extent of a given size, but this is a good start.
+ *
+ * Callers of this must check if cache->cached == BTRFS_CACHE_ERROR before using
+ * any of the information in this block group.
+ */
+void btrfs_wait_block_group_cache_progress(struct btrfs_block_group *cache,
+					   u64 num_bytes)
+{
+	struct btrfs_caching_control *caching_ctl;
+	int progress;
+
+	caching_ctl = btrfs_get_caching_control(cache);
+	if (!caching_ctl)
+		return;
+
+	/*
+	 * We've already failed to allocate from this block group, so even if
+	 * there's enough space in the block group it isn't contiguous enough to
+	 * allow for an allocation, so wait for at least the next wakeup tick,
+	 * or for the thing to be done.
+	 */
+	progress = atomic_read(&caching_ctl->progress);
+
+	wait_event(caching_ctl->wait, btrfs_block_group_done(cache) ||
+		   (progress != atomic_read(&caching_ctl->progress) &&
+		    (cache->free_space_ctl->free_space >= num_bytes)));
+
+	btrfs_put_caching_control(caching_ctl);
+}
+
+static int btrfs_caching_ctl_wait_done(struct btrfs_block_group *cache,
+				       struct btrfs_caching_control *caching_ctl)
+{
+	wait_event(caching_ctl->wait, btrfs_block_group_done(cache));
+	return cache->cached == BTRFS_CACHE_ERROR ? -EIO : 0;
+}
+
+static int btrfs_wait_block_group_cache_done(struct btrfs_block_group *cache)
+{
+	struct btrfs_caching_control *caching_ctl;
+	int ret;
+
+	caching_ctl = btrfs_get_caching_control(cache);
+	if (!caching_ctl)
+		return (cache->cached == BTRFS_CACHE_ERROR) ? -EIO : 0;
+	ret = btrfs_caching_ctl_wait_done(cache, caching_ctl);
+	btrfs_put_caching_control(caching_ctl);
+	return ret;
+}
+
+#ifdef CONFIG_BTRFS_DEBUG
+static void fragment_free_space(struct btrfs_block_group *block_group)
+{
+	struct btrfs_fs_info *fs_info = block_group->fs_info;
+	u64 start = block_group->start;
+	u64 len = block_group->length;
+	u64 chunk = block_group->flags & BTRFS_BLOCK_GROUP_METADATA ?
+		fs_info->nodesize : fs_info->sectorsize;
+	u64 step = chunk << 1;
+
+	while (len > chunk) {
+		btrfs_remove_free_space(block_group, start, chunk);
+		start += step;
+		if (len < step)
+			len = 0;
+		else
+			len -= step;
+	}
+}
+#endif
+
+/*
+ * Add a free space range to the in memory free space cache of a block group.
+ * This checks if the range contains super block locations and any such
+ * locations are not added to the free space cache.
+ *
+ * @block_group:      The target block group.
+ * @start:            Start offset of the range.
+ * @end:              End offset of the range (exclusive).
+ * @total_added_ret:  Optional pointer to return the total amount of space
+ *                    added to the block group's free space cache.
+ *
+ * Returns 0 on success or < 0 on error.
+ */
+int btrfs_add_new_free_space(struct btrfs_block_group *block_group, u64 start,
+			     u64 end, u64 *total_added_ret)
+{
+	struct btrfs_fs_info *info = block_group->fs_info;
+	u64 extent_start, extent_end, size;
+	int ret;
+
+	if (total_added_ret)
+		*total_added_ret = 0;
+
+	while (start < end) {
+		if (!find_first_extent_bit(&info->excluded_extents, start,
+					   &extent_start, &extent_end,
+					   EXTENT_DIRTY | EXTENT_UPTODATE,
+					   NULL))
+			break;
+
+		if (extent_start <= start) {
+			start = extent_end + 1;
+		} else if (extent_start > start && extent_start < end) {
+			size = extent_start - start;
+			ret = btrfs_add_free_space_async_trimmed(block_group,
+								 start, size);
+			if (ret)
+				return ret;
+			if (total_added_ret)
+				*total_added_ret += size;
+			start = extent_end + 1;
+		} else {
+			break;
+		}
+	}
+
+	if (start < end) {
+		size = end - start;
+		ret = btrfs_add_free_space_async_trimmed(block_group, start,
+							 size);
+		if (ret)
+			return ret;
+		if (total_added_ret)
+			*total_added_ret += size;
+	}
+
+	return 0;
+}
+
+/*
+ * Get an arbitrary extent item index / max_index through the block group
+ *
+ * @block_group   the block group to sample from
+ * @index:        the integral step through the block group to grab from
+ * @max_index:    the granularity of the sampling
+ * @key:          return value parameter for the item we find
+ *
+ * Pre-conditions on indices:
+ * 0 <= index <= max_index
+ * 0 < max_index
+ *
+ * Returns: 0 on success, 1 if the search didn't yield a useful item, negative
+ * error code on error.
+ */
+static int sample_block_group_extent_item(struct btrfs_caching_control *caching_ctl,
+					  struct btrfs_block_group *block_group,
+					  int index, int max_index,
+					  struct btrfs_key *found_key)
+{
+	struct btrfs_fs_info *fs_info = block_group->fs_info;
+	struct btrfs_root *extent_root;
+	u64 search_offset;
+	u64 search_end = block_group->start + block_group->length;
+	struct btrfs_path *path;
+	struct btrfs_key search_key;
+	int ret = 0;
+
+	ASSERT(index >= 0);
+	ASSERT(index <= max_index);
+	ASSERT(max_index > 0);
+	lockdep_assert_held(&caching_ctl->mutex);
+	lockdep_assert_held_read(&fs_info->commit_root_sem);
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	extent_root = btrfs_extent_root(fs_info, max_t(u64, block_group->start,
+						       BTRFS_SUPER_INFO_OFFSET));
+
+	path->skip_locking = 1;
+	path->search_commit_root = 1;
+	path->reada = READA_FORWARD;
+
+	search_offset = index * div_u64(block_group->length, max_index);
+	search_key.objectid = block_group->start + search_offset;
+	search_key.type = BTRFS_EXTENT_ITEM_KEY;
+	search_key.offset = 0;
+
+	btrfs_for_each_slot(extent_root, &search_key, found_key, path, ret) {
+		/* Success; sampled an extent item in the block group */
+		if (found_key->type == BTRFS_EXTENT_ITEM_KEY &&
+		    found_key->objectid >= block_group->start &&
+		    found_key->objectid + found_key->offset <= search_end)
+			break;
+
+		/* We can't possibly find a valid extent item anymore */
+		if (found_key->objectid >= search_end) {
+			ret = 1;
+			break;
+		}
+	}
+
+	lockdep_assert_held(&caching_ctl->mutex);
+	lockdep_assert_held_read(&fs_info->commit_root_sem);
+	btrfs_free_path(path);
+	return ret;
+}
+
+/*
+ * Best effort attempt to compute a block group's size class while caching it.
+ *
+ * @block_group: the block group we are caching
+ *
+ * We cannot infer the size class while adding free space extents, because that
+ * logic doesn't care about contiguous file extents (it doesn't differentiate
+ * between a 100M extent and 100 contiguous 1M extents). So we need to read the
+ * file extent items. Reading all of them is quite wasteful, because usually
+ * only a handful are enough to give a good answer. Therefore, we just grab 5 of
+ * them at even steps through the block group and pick the smallest size class
+ * we see. Since size class is best effort, and not guaranteed in general,
+ * inaccuracy is acceptable.
+ *
+ * To be more explicit about why this algorithm makes sense:
+ *
+ * If we are caching in a block group from disk, then there are three major cases
+ * to consider:
+ * 1. the block group is well behaved and all extents in it are the same size
+ *    class.
+ * 2. the block group is mostly one size class with rare exceptions for last
+ *    ditch allocations
+ * 3. the block group was populated before size classes and can have a totally
+ *    arbitrary mix of size classes.
+ *
+ * In case 1, looking at any extent in the block group will yield the correct
+ * result. For the mixed cases, taking the minimum size class seems like a good
+ * approximation, since gaps from frees will be usable to the size class. For
+ * 2., a small handful of file extents is likely to yield the right answer. For
+ * 3, we can either read every file extent, or admit that this is best effort
+ * anyway and try to stay fast.
+ *
+ * Returns: 0 on success, negative error code on error.
+ */
+static int load_block_group_size_class(struct btrfs_caching_control *caching_ctl,
+				       struct btrfs_block_group *block_group)
+{
+	struct btrfs_fs_info *fs_info = block_group->fs_info;
+	struct btrfs_key key;
+	int i;
+	u64 min_size = block_group->length;
+	enum btrfs_block_group_size_class size_class = BTRFS_BG_SZ_NONE;
+	int ret;
+
+	if (!btrfs_block_group_should_use_size_class(block_group))
+		return 0;
+
+	lockdep_assert_held(&caching_ctl->mutex);
+	lockdep_assert_held_read(&fs_info->commit_root_sem);
+	for (i = 0; i < 5; ++i) {
+		ret = sample_block_group_extent_item(caching_ctl, block_group, i, 5, &key);
+		if (ret < 0)
+			goto out;
+		if (ret > 0)
+			continue;
+		min_size = min_t(u64, min_size, key.offset);
+		size_class = btrfs_calc_block_group_size_class(min_size);
+	}
+	if (size_class != BTRFS_BG_SZ_NONE) {
+		spin_lock(&block_group->lock);
+		block_group->size_class = size_class;
+		spin_unlock(&block_group->lock);
+	}
+out:
+	return ret;
+}
+
+static int load_extent_tree_free(struct btrfs_caching_control *caching_ctl)
+{
+	struct btrfs_block_group *block_group = caching_ctl->block_group;
+	struct btrfs_fs_info *fs_info = block_group->fs_info;
+	struct btrfs_root *extent_root;
+	struct btrfs_path *path;
+	struct extent_buffer *leaf;
+	struct btrfs_key key;
+	u64 total_found = 0;
+	u64 last = 0;
+	u32 nritems;
+	int ret;
+	bool wakeup = true;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	last = max_t(u64, block_group->start, BTRFS_SUPER_INFO_OFFSET);
+	extent_root = btrfs_extent_root(fs_info, last);
+
+#ifdef CONFIG_BTRFS_DEBUG
+	/*
+	 * If we're fragmenting we don't want to make anybody think we can
+	 * allocate from this block group until we've had a chance to fragment
+	 * the free space.
+	 */
+	if (btrfs_should_fragment_free_space(block_group))
+		wakeup = false;
+#endif
+	/*
+	 * We don't want to deadlock with somebody trying to allocate a new
+	 * extent for the extent root while also trying to search the extent
+	 * root to add free space.  So we skip locking and search the commit
+	 * root, since its read-only
+	 */
+	path->skip_locking = 1;
+	path->search_commit_root = 1;
+	path->reada = READA_FORWARD;
+
+	key.objectid = last;
+	key.offset = 0;
+	key.type = BTRFS_EXTENT_ITEM_KEY;
+
+next:
+	ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
+	if (ret < 0)
+		goto out;
+
+	leaf = path->nodes[0];
+	nritems = btrfs_header_nritems(leaf);
+
+	while (1) {
+		if (btrfs_fs_closing(fs_info) > 1) {
+			last = (u64)-1;
+			break;
+		}
+
+		if (path->slots[0] < nritems) {
+			btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
+		} else {
+			ret = btrfs_find_next_key(extent_root, path, &key, 0, 0);
+			if (ret)
+				break;
+
+			if (need_resched() ||
+			    rwsem_is_contended(&fs_info->commit_root_sem)) {
+				btrfs_release_path(path);
+				up_read(&fs_info->commit_root_sem);
+				mutex_unlock(&caching_ctl->mutex);
+				cond_resched();
+				mutex_lock(&caching_ctl->mutex);
+				down_read(&fs_info->commit_root_sem);
+				goto next;
+			}
+
+			ret = btrfs_next_leaf(extent_root, path);
+			if (ret < 0)
+				goto out;
+			if (ret)
+				break;
+			leaf = path->nodes[0];
+			nritems = btrfs_header_nritems(leaf);
+			continue;
+		}
+
+		if (key.objectid < last) {
+			key.objectid = last;
+			key.offset = 0;
+			key.type = BTRFS_EXTENT_ITEM_KEY;
+			btrfs_release_path(path);
+			goto next;
+		}
+
+		if (key.objectid < block_group->start) {
+			path->slots[0]++;
+			continue;
+		}
+
+		if (key.objectid >= block_group->start + block_group->length)
+			break;
+
+		if (key.type == BTRFS_EXTENT_ITEM_KEY ||
+		    key.type == BTRFS_METADATA_ITEM_KEY) {
+			u64 space_added;
+
+			ret = btrfs_add_new_free_space(block_group, last,
+						       key.objectid, &space_added);
+			if (ret)
+				goto out;
+			total_found += space_added;
+			if (key.type == BTRFS_METADATA_ITEM_KEY)
+				last = key.objectid +
+					fs_info->nodesize;
+			else
+				last = key.objectid + key.offset;
+
+			if (total_found > CACHING_CTL_WAKE_UP) {
+				total_found = 0;
+				if (wakeup) {
+					atomic_inc(&caching_ctl->progress);
+					wake_up(&caching_ctl->wait);
+				}
+			}
+		}
+		path->slots[0]++;
+	}
+
+	ret = btrfs_add_new_free_space(block_group, last,
+				       block_group->start + block_group->length,
+				       NULL);
+out:
+	btrfs_free_path(path);
+	return ret;
+}
+
+static inline void btrfs_free_excluded_extents(const struct btrfs_block_group *bg)
+{
+	clear_extent_bits(&bg->fs_info->excluded_extents, bg->start,
+			  bg->start + bg->length - 1, EXTENT_UPTODATE);
+}
+
+static noinline void caching_thread(struct btrfs_work *work)
+{
+	struct btrfs_block_group *block_group;
+	struct btrfs_fs_info *fs_info;
+	struct btrfs_caching_control *caching_ctl;
+	int ret;
+
+	caching_ctl = container_of(work, struct btrfs_caching_control, work);
+	block_group = caching_ctl->block_group;
+	fs_info = block_group->fs_info;
+
+	mutex_lock(&caching_ctl->mutex);
+	down_read(&fs_info->commit_root_sem);
+
+	load_block_group_size_class(caching_ctl, block_group);
+	if (btrfs_test_opt(fs_info, SPACE_CACHE)) {
+		ret = load_free_space_cache(block_group);
+		if (ret == 1) {
+			ret = 0;
+			goto done;
+		}
+
+		/*
+		 * We failed to load the space cache, set ourselves to
+		 * CACHE_STARTED and carry on.
+		 */
+		spin_lock(&block_group->lock);
+		block_group->cached = BTRFS_CACHE_STARTED;
+		spin_unlock(&block_group->lock);
+		wake_up(&caching_ctl->wait);
+	}
+
+	/*
+	 * If we are in the transaction that populated the free space tree we
+	 * can't actually cache from the free space tree as our commit root and
+	 * real root are the same, so we could change the contents of the blocks
+	 * while caching.  Instead do the slow caching in this case, and after
+	 * the transaction has committed we will be safe.
+	 */
+	if (btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE) &&
+	    !(test_bit(BTRFS_FS_FREE_SPACE_TREE_UNTRUSTED, &fs_info->flags)))
+		ret = load_free_space_tree(caching_ctl);
+	else
+		ret = load_extent_tree_free(caching_ctl);
+done:
+	spin_lock(&block_group->lock);
+	block_group->caching_ctl = NULL;
+	block_group->cached = ret ? BTRFS_CACHE_ERROR : BTRFS_CACHE_FINISHED;
+	spin_unlock(&block_group->lock);
+
+#ifdef CONFIG_BTRFS_DEBUG
+	if (btrfs_should_fragment_free_space(block_group)) {
+		u64 bytes_used;
+
+		spin_lock(&block_group->space_info->lock);
+		spin_lock(&block_group->lock);
+		bytes_used = block_group->length - block_group->used;
+		block_group->space_info->bytes_used += bytes_used >> 1;
+		spin_unlock(&block_group->lock);
+		spin_unlock(&block_group->space_info->lock);
+		fragment_free_space(block_group);
+	}
+#endif
+
+	up_read(&fs_info->commit_root_sem);
+	btrfs_free_excluded_extents(block_group);
+	mutex_unlock(&caching_ctl->mutex);
+
+	wake_up(&caching_ctl->wait);
+
+	btrfs_put_caching_control(caching_ctl);
+	btrfs_put_block_group(block_group);
+}
+
+int btrfs_cache_block_group(struct btrfs_block_group *cache, bool wait)
+{
+	struct btrfs_fs_info *fs_info = cache->fs_info;
+	struct btrfs_caching_control *caching_ctl = NULL;
+	int ret = 0;
+
+	/* Allocator for zoned filesystems does not use the cache at all */
+	if (btrfs_is_zoned(fs_info))
+		return 0;
+
+	caching_ctl = kzalloc(sizeof(*caching_ctl), GFP_NOFS);
+	if (!caching_ctl)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&caching_ctl->list);
+	mutex_init(&caching_ctl->mutex);
+	init_waitqueue_head(&caching_ctl->wait);
+	caching_ctl->block_group = cache;
+	refcount_set(&caching_ctl->count, 2);
+	atomic_set(&caching_ctl->progress, 0);
+	btrfs_init_work(&caching_ctl->work, caching_thread, NULL, NULL);
+
+	spin_lock(&cache->lock);
+	if (cache->cached != BTRFS_CACHE_NO) {
+		kfree(caching_ctl);
+
+		caching_ctl = cache->caching_ctl;
+		if (caching_ctl)
+			refcount_inc(&caching_ctl->count);
+		spin_unlock(&cache->lock);
+		goto out;
+	}
+	WARN_ON(cache->caching_ctl);
+	cache->caching_ctl = caching_ctl;
+	cache->cached = BTRFS_CACHE_STARTED;
+	spin_unlock(&cache->lock);
+
+	write_lock(&fs_info->block_group_cache_lock);
+	refcount_inc(&caching_ctl->count);
+	list_add_tail(&caching_ctl->list, &fs_info->caching_block_groups);
+	write_unlock(&fs_info->block_group_cache_lock);
+
+	btrfs_get_block_group(cache);
+
+	btrfs_queue_work(fs_info->caching_workers, &caching_ctl->work);
+out:
+	if (wait && caching_ctl)
+		ret = btrfs_caching_ctl_wait_done(cache, caching_ctl);
+	if (caching_ctl)
+		btrfs_put_caching_control(caching_ctl);
+
+	return ret;
+}
+
+static void clear_avail_alloc_bits(struct btrfs_fs_info *fs_info, u64 flags)
+{
+	u64 extra_flags = chunk_to_extended(flags) &
+				BTRFS_EXTENDED_PROFILE_MASK;
+
+	write_seqlock(&fs_info->profiles_lock);
+	if (flags & BTRFS_BLOCK_GROUP_DATA)
+		fs_info->avail_data_alloc_bits &= ~extra_flags;
+	if (flags & BTRFS_BLOCK_GROUP_METADATA)
+		fs_info->avail_metadata_alloc_bits &= ~extra_flags;
+	if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
+		fs_info->avail_system_alloc_bits &= ~extra_flags;
+	write_sequnlock(&fs_info->profiles_lock);
+}
+
+/*
+ * Clear incompat bits for the following feature(s):
+ *
+ * - RAID56 - in case there's neither RAID5 nor RAID6 profile block group
+ *            in the whole filesystem
+ *
+ * - RAID1C34 - same as above for RAID1C3 and RAID1C4 block groups
+ */
+static void clear_incompat_bg_bits(struct btrfs_fs_info *fs_info, u64 flags)
+{
+	bool found_raid56 = false;
+	bool found_raid1c34 = false;
+
+	if ((flags & BTRFS_BLOCK_GROUP_RAID56_MASK) ||
+	    (flags & BTRFS_BLOCK_GROUP_RAID1C3) ||
+	    (flags & BTRFS_BLOCK_GROUP_RAID1C4)) {
+		struct list_head *head = &fs_info->space_info;
+		struct btrfs_space_info *sinfo;
+
+		list_for_each_entry_rcu(sinfo, head, list) {
+			down_read(&sinfo->groups_sem);
+			if (!list_empty(&sinfo->block_groups[BTRFS_RAID_RAID5]))
+				found_raid56 = true;
+			if (!list_empty(&sinfo->block_groups[BTRFS_RAID_RAID6]))
+				found_raid56 = true;
+			if (!list_empty(&sinfo->block_groups[BTRFS_RAID_RAID1C3]))
+				found_raid1c34 = true;
+			if (!list_empty(&sinfo->block_groups[BTRFS_RAID_RAID1C4]))
+				found_raid1c34 = true;
+			up_read(&sinfo->groups_sem);
+		}
+		if (!found_raid56)
+			btrfs_clear_fs_incompat(fs_info, RAID56);
+		if (!found_raid1c34)
+			btrfs_clear_fs_incompat(fs_info, RAID1C34);
+	}
+}
+
+static int remove_block_group_item(struct btrfs_trans_handle *trans,
+				   struct btrfs_path *path,
+				   struct btrfs_block_group *block_group)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_root *root;
+	struct btrfs_key key;
+	int ret;
+
+	root = btrfs_block_group_root(fs_info);
+	key.objectid = block_group->start;
+	key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
+	key.offset = block_group->length;
+
+	ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
+	if (ret > 0)
+		ret = -ENOENT;
+	if (ret < 0)
+		return ret;
+
+	ret = btrfs_del_item(trans, root, path);
+	return ret;
+}
+
+int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
+			     u64 group_start, struct extent_map *em)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_path *path;
+	struct btrfs_block_group *block_group;
+	struct btrfs_free_cluster *cluster;
+	struct inode *inode;
+	struct kobject *kobj = NULL;
+	int ret;
+	int index;
+	int factor;
+	struct btrfs_caching_control *caching_ctl = NULL;
+	bool remove_em;
+	bool remove_rsv = false;
+
+	block_group = btrfs_lookup_block_group(fs_info, group_start);
+	BUG_ON(!block_group);
+	BUG_ON(!block_group->ro);
+
+	trace_btrfs_remove_block_group(block_group);
+	/*
+	 * Free the reserved super bytes from this block group before
+	 * remove it.
+	 */
+	btrfs_free_excluded_extents(block_group);
+	btrfs_free_ref_tree_range(fs_info, block_group->start,
+				  block_group->length);
+
+	index = btrfs_bg_flags_to_raid_index(block_group->flags);
+	factor = btrfs_bg_type_to_factor(block_group->flags);
+
+	/* make sure this block group isn't part of an allocation cluster */
+	cluster = &fs_info->data_alloc_cluster;
+	spin_lock(&cluster->refill_lock);
+	btrfs_return_cluster_to_free_space(block_group, cluster);
+	spin_unlock(&cluster->refill_lock);
+
+	/*
+	 * make sure this block group isn't part of a metadata
+	 * allocation cluster
+	 */
+	cluster = &fs_info->meta_alloc_cluster;
+	spin_lock(&cluster->refill_lock);
+	btrfs_return_cluster_to_free_space(block_group, cluster);
+	spin_unlock(&cluster->refill_lock);
+
+	btrfs_clear_treelog_bg(block_group);
+	btrfs_clear_data_reloc_bg(block_group);
+
+	path = btrfs_alloc_path();
+	if (!path) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	/*
+	 * get the inode first so any iput calls done for the io_list
+	 * aren't the final iput (no unlinks allowed now)
+	 */
+	inode = lookup_free_space_inode(block_group, path);
+
+	mutex_lock(&trans->transaction->cache_write_mutex);
+	/*
+	 * Make sure our free space cache IO is done before removing the
+	 * free space inode
+	 */
+	spin_lock(&trans->transaction->dirty_bgs_lock);
+	if (!list_empty(&block_group->io_list)) {
+		list_del_init(&block_group->io_list);
+
+		WARN_ON(!IS_ERR(inode) && inode != block_group->io_ctl.inode);
+
+		spin_unlock(&trans->transaction->dirty_bgs_lock);
+		btrfs_wait_cache_io(trans, block_group, path);
+		btrfs_put_block_group(block_group);
+		spin_lock(&trans->transaction->dirty_bgs_lock);
+	}
+
+	if (!list_empty(&block_group->dirty_list)) {
+		list_del_init(&block_group->dirty_list);
+		remove_rsv = true;
+		btrfs_put_block_group(block_group);
+	}
+	spin_unlock(&trans->transaction->dirty_bgs_lock);
+	mutex_unlock(&trans->transaction->cache_write_mutex);
+
+	ret = btrfs_remove_free_space_inode(trans, inode, block_group);
+	if (ret)
+		goto out;
+
+	write_lock(&fs_info->block_group_cache_lock);
+	rb_erase_cached(&block_group->cache_node,
+			&fs_info->block_group_cache_tree);
+	RB_CLEAR_NODE(&block_group->cache_node);
+
+	/* Once for the block groups rbtree */
+	btrfs_put_block_group(block_group);
+
+	write_unlock(&fs_info->block_group_cache_lock);
+
+	down_write(&block_group->space_info->groups_sem);
+	/*
+	 * we must use list_del_init so people can check to see if they
+	 * are still on the list after taking the semaphore
+	 */
+	list_del_init(&block_group->list);
+	if (list_empty(&block_group->space_info->block_groups[index])) {
+		kobj = block_group->space_info->block_group_kobjs[index];
+		block_group->space_info->block_group_kobjs[index] = NULL;
+		clear_avail_alloc_bits(fs_info, block_group->flags);
+	}
+	up_write(&block_group->space_info->groups_sem);
+	clear_incompat_bg_bits(fs_info, block_group->flags);
+	if (kobj) {
+		kobject_del(kobj);
+		kobject_put(kobj);
+	}
+
+	if (block_group->cached == BTRFS_CACHE_STARTED)
+		btrfs_wait_block_group_cache_done(block_group);
+
+	write_lock(&fs_info->block_group_cache_lock);
+	caching_ctl = btrfs_get_caching_control(block_group);
+	if (!caching_ctl) {
+		struct btrfs_caching_control *ctl;
+
+		list_for_each_entry(ctl, &fs_info->caching_block_groups, list) {
+			if (ctl->block_group == block_group) {
+				caching_ctl = ctl;
+				refcount_inc(&caching_ctl->count);
+				break;
+			}
+		}
+	}
+	if (caching_ctl)
+		list_del_init(&caching_ctl->list);
+	write_unlock(&fs_info->block_group_cache_lock);
+
+	if (caching_ctl) {
+		/* Once for the caching bgs list and once for us. */
+		btrfs_put_caching_control(caching_ctl);
+		btrfs_put_caching_control(caching_ctl);
+	}
+
+	spin_lock(&trans->transaction->dirty_bgs_lock);
+	WARN_ON(!list_empty(&block_group->dirty_list));
+	WARN_ON(!list_empty(&block_group->io_list));
+	spin_unlock(&trans->transaction->dirty_bgs_lock);
+
+	btrfs_remove_free_space_cache(block_group);
+
+	spin_lock(&block_group->space_info->lock);
+	list_del_init(&block_group->ro_list);
+
+	if (btrfs_test_opt(fs_info, ENOSPC_DEBUG)) {
+		WARN_ON(block_group->space_info->total_bytes
+			< block_group->length);
+		WARN_ON(block_group->space_info->bytes_readonly
+			< block_group->length - block_group->zone_unusable);
+		WARN_ON(block_group->space_info->bytes_zone_unusable
+			< block_group->zone_unusable);
+		WARN_ON(block_group->space_info->disk_total
+			< block_group->length * factor);
+	}
+	block_group->space_info->total_bytes -= block_group->length;
+	block_group->space_info->bytes_readonly -=
+		(block_group->length - block_group->zone_unusable);
+	block_group->space_info->bytes_zone_unusable -=
+		block_group->zone_unusable;
+	block_group->space_info->disk_total -= block_group->length * factor;
+
+	spin_unlock(&block_group->space_info->lock);
+
+	/*
+	 * Remove the free space for the block group from the free space tree
+	 * and the block group's item from the extent tree before marking the
+	 * block group as removed. This is to prevent races with tasks that
+	 * freeze and unfreeze a block group, this task and another task
+	 * allocating a new block group - the unfreeze task ends up removing
+	 * the block group's extent map before the task calling this function
+	 * deletes the block group item from the extent tree, allowing for
+	 * another task to attempt to create another block group with the same
+	 * item key (and failing with -EEXIST and a transaction abort).
+	 */
+	ret = remove_block_group_free_space(trans, block_group);
+	if (ret)
+		goto out;
+
+	ret = remove_block_group_item(trans, path, block_group);
+	if (ret < 0)
+		goto out;
+
+	spin_lock(&block_group->lock);
+	set_bit(BLOCK_GROUP_FLAG_REMOVED, &block_group->runtime_flags);
+
+	/*
+	 * At this point trimming or scrub can't start on this block group,
+	 * because we removed the block group from the rbtree
+	 * fs_info->block_group_cache_tree so no one can't find it anymore and
+	 * even if someone already got this block group before we removed it
+	 * from the rbtree, they have already incremented block_group->frozen -
+	 * if they didn't, for the trimming case they won't find any free space
+	 * entries because we already removed them all when we called
+	 * btrfs_remove_free_space_cache().
+	 *
+	 * And we must not remove the extent map from the fs_info->mapping_tree
+	 * to prevent the same logical address range and physical device space
+	 * ranges from being reused for a new block group. This is needed to
+	 * avoid races with trimming and scrub.
+	 *
+	 * An fs trim operation (btrfs_trim_fs() / btrfs_ioctl_fitrim()) is
+	 * completely transactionless, so while it is trimming a range the
+	 * currently running transaction might finish and a new one start,
+	 * allowing for new block groups to be created that can reuse the same
+	 * physical device locations unless we take this special care.
+	 *
+	 * There may also be an implicit trim operation if the file system
+	 * is mounted with -odiscard. The same protections must remain
+	 * in place until the extents have been discarded completely when
+	 * the transaction commit has completed.
+	 */
+	remove_em = (atomic_read(&block_group->frozen) == 0);
+	spin_unlock(&block_group->lock);
+
+	if (remove_em) {
+		struct extent_map_tree *em_tree;
+
+		em_tree = &fs_info->mapping_tree;
+		write_lock(&em_tree->lock);
+		remove_extent_mapping(em_tree, em);
+		write_unlock(&em_tree->lock);
+		/* once for the tree */
+		free_extent_map(em);
+	}
+
+out:
+	/* Once for the lookup reference */
+	btrfs_put_block_group(block_group);
+	if (remove_rsv)
+		btrfs_delayed_refs_rsv_release(fs_info, 1);
+	btrfs_free_path(path);
+	return ret;
+}
+
+struct btrfs_trans_handle *btrfs_start_trans_remove_block_group(
+		struct btrfs_fs_info *fs_info, const u64 chunk_offset)
+{
+	struct btrfs_root *root = btrfs_block_group_root(fs_info);
+	struct extent_map_tree *em_tree = &fs_info->mapping_tree;
+	struct extent_map *em;
+	struct map_lookup *map;
+	unsigned int num_items;
+
+	read_lock(&em_tree->lock);
+	em = lookup_extent_mapping(em_tree, chunk_offset, 1);
+	read_unlock(&em_tree->lock);
+	ASSERT(em && em->start == chunk_offset);
+
+	/*
+	 * We need to reserve 3 + N units from the metadata space info in order
+	 * to remove a block group (done at btrfs_remove_chunk() and at
+	 * btrfs_remove_block_group()), which are used for:
+	 *
+	 * 1 unit for adding the free space inode's orphan (located in the tree
+	 * of tree roots).
+	 * 1 unit for deleting the block group item (located in the extent
+	 * tree).
+	 * 1 unit for deleting the free space item (located in tree of tree
+	 * roots).
+	 * N units for deleting N device extent items corresponding to each
+	 * stripe (located in the device tree).
+	 *
+	 * In order to remove a block group we also need to reserve units in the
+	 * system space info in order to update the chunk tree (update one or
+	 * more device items and remove one chunk item), but this is done at
+	 * btrfs_remove_chunk() through a call to check_system_chunk().
+	 */
+	map = em->map_lookup;
+	num_items = 3 + map->num_stripes;
+	free_extent_map(em);
+
+	return btrfs_start_transaction_fallback_global_rsv(root, num_items);
+}
+
+/*
+ * Mark block group @cache read-only, so later write won't happen to block
+ * group @cache.
+ *
+ * If @force is not set, this function will only mark the block group readonly
+ * if we have enough free space (1M) in other metadata/system block groups.
+ * If @force is not set, this function will mark the block group readonly
+ * without checking free space.
+ *
+ * NOTE: This function doesn't care if other block groups can contain all the
+ * data in this block group. That check should be done by relocation routine,
+ * not this function.
+ */
+static int inc_block_group_ro(struct btrfs_block_group *cache, int force)
+{
+	struct btrfs_space_info *sinfo = cache->space_info;
+	u64 num_bytes;
+	int ret = -ENOSPC;
+
+	spin_lock(&sinfo->lock);
+	spin_lock(&cache->lock);
+
+	if (cache->swap_extents) {
+		ret = -ETXTBSY;
+		goto out;
+	}
+
+	if (cache->ro) {
+		cache->ro++;
+		ret = 0;
+		goto out;
+	}
+
+	num_bytes = cache->length - cache->reserved - cache->pinned -
+		    cache->bytes_super - cache->zone_unusable - cache->used;
+
+	/*
+	 * Data never overcommits, even in mixed mode, so do just the straight
+	 * check of left over space in how much we have allocated.
+	 */
+	if (force) {
+		ret = 0;
+	} else if (sinfo->flags & BTRFS_BLOCK_GROUP_DATA) {
+		u64 sinfo_used = btrfs_space_info_used(sinfo, true);
+
+		/*
+		 * Here we make sure if we mark this bg RO, we still have enough
+		 * free space as buffer.
+		 */
+		if (sinfo_used + num_bytes <= sinfo->total_bytes)
+			ret = 0;
+	} else {
+		/*
+		 * We overcommit metadata, so we need to do the
+		 * btrfs_can_overcommit check here, and we need to pass in
+		 * BTRFS_RESERVE_NO_FLUSH to give ourselves the most amount of
+		 * leeway to allow us to mark this block group as read only.
+		 */
+		if (btrfs_can_overcommit(cache->fs_info, sinfo, num_bytes,
+					 BTRFS_RESERVE_NO_FLUSH))
+			ret = 0;
+	}
+
+	if (!ret) {
+		sinfo->bytes_readonly += num_bytes;
+		if (btrfs_is_zoned(cache->fs_info)) {
+			/* Migrate zone_unusable bytes to readonly */
+			sinfo->bytes_readonly += cache->zone_unusable;
+			sinfo->bytes_zone_unusable -= cache->zone_unusable;
+			cache->zone_unusable = 0;
+		}
+		cache->ro++;
+		list_add_tail(&cache->ro_list, &sinfo->ro_bgs);
+	}
+out:
+	spin_unlock(&cache->lock);
+	spin_unlock(&sinfo->lock);
+	if (ret == -ENOSPC && btrfs_test_opt(cache->fs_info, ENOSPC_DEBUG)) {
+		btrfs_info(cache->fs_info,
+			"unable to make block group %llu ro", cache->start);
+		btrfs_dump_space_info(cache->fs_info, cache->space_info, 0, 0);
+	}
+	return ret;
+}
+
+static bool clean_pinned_extents(struct btrfs_trans_handle *trans,
+				 struct btrfs_block_group *bg)
+{
+	struct btrfs_fs_info *fs_info = bg->fs_info;
+	struct btrfs_transaction *prev_trans = NULL;
+	const u64 start = bg->start;
+	const u64 end = start + bg->length - 1;
+	int ret;
+
+	spin_lock(&fs_info->trans_lock);
+	if (trans->transaction->list.prev != &fs_info->trans_list) {
+		prev_trans = list_last_entry(&trans->transaction->list,
+					     struct btrfs_transaction, list);
+		refcount_inc(&prev_trans->use_count);
+	}
+	spin_unlock(&fs_info->trans_lock);
+
+	/*
+	 * Hold the unused_bg_unpin_mutex lock to avoid racing with
+	 * btrfs_finish_extent_commit(). If we are at transaction N, another
+	 * task might be running finish_extent_commit() for the previous
+	 * transaction N - 1, and have seen a range belonging to the block
+	 * group in pinned_extents before we were able to clear the whole block
+	 * group range from pinned_extents. This means that task can lookup for
+	 * the block group after we unpinned it from pinned_extents and removed
+	 * it, leading to a BUG_ON() at unpin_extent_range().
+	 */
+	mutex_lock(&fs_info->unused_bg_unpin_mutex);
+	if (prev_trans) {
+		ret = clear_extent_bits(&prev_trans->pinned_extents, start, end,
+					EXTENT_DIRTY);
+		if (ret)
+			goto out;
+	}
+
+	ret = clear_extent_bits(&trans->transaction->pinned_extents, start, end,
+				EXTENT_DIRTY);
+out:
+	mutex_unlock(&fs_info->unused_bg_unpin_mutex);
+	if (prev_trans)
+		btrfs_put_transaction(prev_trans);
+
+	return ret == 0;
+}
+
+/*
+ * Process the unused_bgs list and remove any that don't have any allocated
+ * space inside of them.
+ */
+void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_block_group *block_group;
+	struct btrfs_space_info *space_info;
+	struct btrfs_trans_handle *trans;
+	const bool async_trim_enabled = btrfs_test_opt(fs_info, DISCARD_ASYNC);
+	int ret = 0;
+
+	if (!test_bit(BTRFS_FS_OPEN, &fs_info->flags))
+		return;
+
+	if (btrfs_fs_closing(fs_info))
+		return;
+
+	/*
+	 * Long running balances can keep us blocked here for eternity, so
+	 * simply skip deletion if we're unable to get the mutex.
+	 */
+	if (!mutex_trylock(&fs_info->reclaim_bgs_lock))
+		return;
+
+	spin_lock(&fs_info->unused_bgs_lock);
+	while (!list_empty(&fs_info->unused_bgs)) {
+		int trimming;
+
+		block_group = list_first_entry(&fs_info->unused_bgs,
+					       struct btrfs_block_group,
+					       bg_list);
+		list_del_init(&block_group->bg_list);
+
+		space_info = block_group->space_info;
+
+		if (ret || btrfs_mixed_space_info(space_info)) {
+			btrfs_put_block_group(block_group);
+			continue;
+		}
+		spin_unlock(&fs_info->unused_bgs_lock);
+
+		btrfs_discard_cancel_work(&fs_info->discard_ctl, block_group);
+
+		/* Don't want to race with allocators so take the groups_sem */
+		down_write(&space_info->groups_sem);
+
+		/*
+		 * Async discard moves the final block group discard to be prior
+		 * to the unused_bgs code path.  Therefore, if it's not fully
+		 * trimmed, punt it back to the async discard lists.
+		 */
+		if (btrfs_test_opt(fs_info, DISCARD_ASYNC) &&
+		    !btrfs_is_free_space_trimmed(block_group)) {
+			trace_btrfs_skip_unused_block_group(block_group);
+			up_write(&space_info->groups_sem);
+			/* Requeue if we failed because of async discard */
+			btrfs_discard_queue_work(&fs_info->discard_ctl,
+						 block_group);
+			goto next;
+		}
+
+		spin_lock(&block_group->lock);
+		if (block_group->reserved || block_group->pinned ||
+		    block_group->used || block_group->ro ||
+		    list_is_singular(&block_group->list)) {
+			/*
+			 * We want to bail if we made new allocations or have
+			 * outstanding allocations in this block group.  We do
+			 * the ro check in case balance is currently acting on
+			 * this block group.
+			 */
+			trace_btrfs_skip_unused_block_group(block_group);
+			spin_unlock(&block_group->lock);
+			up_write(&space_info->groups_sem);
+			goto next;
+		}
+		spin_unlock(&block_group->lock);
+
+		/* We don't want to force the issue, only flip if it's ok. */
+		ret = inc_block_group_ro(block_group, 0);
+		up_write(&space_info->groups_sem);
+		if (ret < 0) {
+			ret = 0;
+			goto next;
+		}
+
+		ret = btrfs_zone_finish(block_group);
+		if (ret < 0) {
+			btrfs_dec_block_group_ro(block_group);
+			if (ret == -EAGAIN)
+				ret = 0;
+			goto next;
+		}
+
+		/*
+		 * Want to do this before we do anything else so we can recover
+		 * properly if we fail to join the transaction.
+		 */
+		trans = btrfs_start_trans_remove_block_group(fs_info,
+						     block_group->start);
+		if (IS_ERR(trans)) {
+			btrfs_dec_block_group_ro(block_group);
+			ret = PTR_ERR(trans);
+			goto next;
+		}
+
+		/*
+		 * We could have pending pinned extents for this block group,
+		 * just delete them, we don't care about them anymore.
+		 */
+		if (!clean_pinned_extents(trans, block_group)) {
+			btrfs_dec_block_group_ro(block_group);
+			goto end_trans;
+		}
+
+		/*
+		 * At this point, the block_group is read only and should fail
+		 * new allocations.  However, btrfs_finish_extent_commit() can
+		 * cause this block_group to be placed back on the discard
+		 * lists because now the block_group isn't fully discarded.
+		 * Bail here and try again later after discarding everything.
+		 */
+		spin_lock(&fs_info->discard_ctl.lock);
+		if (!list_empty(&block_group->discard_list)) {
+			spin_unlock(&fs_info->discard_ctl.lock);
+			btrfs_dec_block_group_ro(block_group);
+			btrfs_discard_queue_work(&fs_info->discard_ctl,
+						 block_group);
+			goto end_trans;
+		}
+		spin_unlock(&fs_info->discard_ctl.lock);
+
+		/* Reset pinned so btrfs_put_block_group doesn't complain */
+		spin_lock(&space_info->lock);
+		spin_lock(&block_group->lock);
+
+		btrfs_space_info_update_bytes_pinned(fs_info, space_info,
+						     -block_group->pinned);
+		space_info->bytes_readonly += block_group->pinned;
+		block_group->pinned = 0;
+
+		spin_unlock(&block_group->lock);
+		spin_unlock(&space_info->lock);
+
+		/*
+		 * The normal path here is an unused block group is passed here,
+		 * then trimming is handled in the transaction commit path.
+		 * Async discard interposes before this to do the trimming
+		 * before coming down the unused block group path as trimming
+		 * will no longer be done later in the transaction commit path.
+		 */
+		if (!async_trim_enabled && btrfs_test_opt(fs_info, DISCARD_ASYNC))
+			goto flip_async;
+
+		/*
+		 * DISCARD can flip during remount. On zoned filesystems, we
+		 * need to reset sequential-required zones.
+		 */
+		trimming = btrfs_test_opt(fs_info, DISCARD_SYNC) ||
+				btrfs_is_zoned(fs_info);
+
+		/* Implicit trim during transaction commit. */
+		if (trimming)
+			btrfs_freeze_block_group(block_group);
+
+		/*
+		 * Btrfs_remove_chunk will abort the transaction if things go
+		 * horribly wrong.
+		 */
+		ret = btrfs_remove_chunk(trans, block_group->start);
+
+		if (ret) {
+			if (trimming)
+				btrfs_unfreeze_block_group(block_group);
+			goto end_trans;
+		}
+
+		/*
+		 * If we're not mounted with -odiscard, we can just forget
+		 * about this block group. Otherwise we'll need to wait
+		 * until transaction commit to do the actual discard.
+		 */
+		if (trimming) {
+			spin_lock(&fs_info->unused_bgs_lock);
+			/*
+			 * A concurrent scrub might have added us to the list
+			 * fs_info->unused_bgs, so use a list_move operation
+			 * to add the block group to the deleted_bgs list.
+			 */
+			list_move(&block_group->bg_list,
+				  &trans->transaction->deleted_bgs);
+			spin_unlock(&fs_info->unused_bgs_lock);
+			btrfs_get_block_group(block_group);
+		}
+end_trans:
+		btrfs_end_transaction(trans);
+next:
+		btrfs_put_block_group(block_group);
+		spin_lock(&fs_info->unused_bgs_lock);
+	}
+	spin_unlock(&fs_info->unused_bgs_lock);
+	mutex_unlock(&fs_info->reclaim_bgs_lock);
+	return;
+
+flip_async:
+	btrfs_end_transaction(trans);
+	mutex_unlock(&fs_info->reclaim_bgs_lock);
+	btrfs_put_block_group(block_group);
+	btrfs_discard_punt_unused_bgs_list(fs_info);
+}
+
+void btrfs_mark_bg_unused(struct btrfs_block_group *bg)
+{
+	struct btrfs_fs_info *fs_info = bg->fs_info;
+
+	spin_lock(&fs_info->unused_bgs_lock);
+	if (list_empty(&bg->bg_list)) {
+		btrfs_get_block_group(bg);
+		trace_btrfs_add_unused_block_group(bg);
+		list_add_tail(&bg->bg_list, &fs_info->unused_bgs);
+	} else if (!test_bit(BLOCK_GROUP_FLAG_NEW, &bg->runtime_flags)) {
+		/* Pull out the block group from the reclaim_bgs list. */
+		trace_btrfs_add_unused_block_group(bg);
+		list_move_tail(&bg->bg_list, &fs_info->unused_bgs);
+	}
+	spin_unlock(&fs_info->unused_bgs_lock);
+}
+
+/*
+ * We want block groups with a low number of used bytes to be in the beginning
+ * of the list, so they will get reclaimed first.
+ */
+static int reclaim_bgs_cmp(void *unused, const struct list_head *a,
+			   const struct list_head *b)
+{
+	const struct btrfs_block_group *bg1, *bg2;
+
+	bg1 = list_entry(a, struct btrfs_block_group, bg_list);
+	bg2 = list_entry(b, struct btrfs_block_group, bg_list);
+
+	return bg1->used > bg2->used;
+}
+
+static inline bool btrfs_should_reclaim(struct btrfs_fs_info *fs_info)
+{
+	if (btrfs_is_zoned(fs_info))
+		return btrfs_zoned_should_reclaim(fs_info);
+	return true;
+}
+
+static bool should_reclaim_block_group(struct btrfs_block_group *bg, u64 bytes_freed)
+{
+	const struct btrfs_space_info *space_info = bg->space_info;
+	const int reclaim_thresh = READ_ONCE(space_info->bg_reclaim_threshold);
+	const u64 new_val = bg->used;
+	const u64 old_val = new_val + bytes_freed;
+	u64 thresh;
+
+	if (reclaim_thresh == 0)
+		return false;
+
+	thresh = mult_perc(bg->length, reclaim_thresh);
+
+	/*
+	 * If we were below the threshold before don't reclaim, we are likely a
+	 * brand new block group and we don't want to relocate new block groups.
+	 */
+	if (old_val < thresh)
+		return false;
+	if (new_val >= thresh)
+		return false;
+	return true;
+}
+
+void btrfs_reclaim_bgs_work(struct work_struct *work)
+{
+	struct btrfs_fs_info *fs_info =
+		container_of(work, struct btrfs_fs_info, reclaim_bgs_work);
+	struct btrfs_block_group *bg;
+	struct btrfs_space_info *space_info;
+
+	if (!test_bit(BTRFS_FS_OPEN, &fs_info->flags))
+		return;
+
+	if (btrfs_fs_closing(fs_info))
+		return;
+
+	if (!btrfs_should_reclaim(fs_info))
+		return;
+
+	sb_start_write(fs_info->sb);
+
+	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE)) {
+		sb_end_write(fs_info->sb);
+		return;
+	}
+
+	/*
+	 * Long running balances can keep us blocked here for eternity, so
+	 * simply skip reclaim if we're unable to get the mutex.
+	 */
+	if (!mutex_trylock(&fs_info->reclaim_bgs_lock)) {
+		btrfs_exclop_finish(fs_info);
+		sb_end_write(fs_info->sb);
+		return;
+	}
+
+	spin_lock(&fs_info->unused_bgs_lock);
+	/*
+	 * Sort happens under lock because we can't simply splice it and sort.
+	 * The block groups might still be in use and reachable via bg_list,
+	 * and their presence in the reclaim_bgs list must be preserved.
+	 */
+	list_sort(NULL, &fs_info->reclaim_bgs, reclaim_bgs_cmp);
+	while (!list_empty(&fs_info->reclaim_bgs)) {
+		u64 zone_unusable;
+		int ret = 0;
+
+		bg = list_first_entry(&fs_info->reclaim_bgs,
+				      struct btrfs_block_group,
+				      bg_list);
+		list_del_init(&bg->bg_list);
+
+		space_info = bg->space_info;
+		spin_unlock(&fs_info->unused_bgs_lock);
+
+		/* Don't race with allocators so take the groups_sem */
+		down_write(&space_info->groups_sem);
+
+		spin_lock(&bg->lock);
+		if (bg->reserved || bg->pinned || bg->ro) {
+			/*
+			 * We want to bail if we made new allocations or have
+			 * outstanding allocations in this block group.  We do
+			 * the ro check in case balance is currently acting on
+			 * this block group.
+			 */
+			spin_unlock(&bg->lock);
+			up_write(&space_info->groups_sem);
+			goto next;
+		}
+		if (bg->used == 0) {
+			/*
+			 * It is possible that we trigger relocation on a block
+			 * group as its extents are deleted and it first goes
+			 * below the threshold, then shortly after goes empty.
+			 *
+			 * In this case, relocating it does delete it, but has
+			 * some overhead in relocation specific metadata, looking
+			 * for the non-existent extents and running some extra
+			 * transactions, which we can avoid by using one of the
+			 * other mechanisms for dealing with empty block groups.
+			 */
+			if (!btrfs_test_opt(fs_info, DISCARD_ASYNC))
+				btrfs_mark_bg_unused(bg);
+			spin_unlock(&bg->lock);
+			up_write(&space_info->groups_sem);
+			goto next;
+
+		}
+		/*
+		 * The block group might no longer meet the reclaim condition by
+		 * the time we get around to reclaiming it, so to avoid
+		 * reclaiming overly full block_groups, skip reclaiming them.
+		 *
+		 * Since the decision making process also depends on the amount
+		 * being freed, pass in a fake giant value to skip that extra
+		 * check, which is more meaningful when adding to the list in
+		 * the first place.
+		 */
+		if (!should_reclaim_block_group(bg, bg->length)) {
+			spin_unlock(&bg->lock);
+			up_write(&space_info->groups_sem);
+			goto next;
+		}
+		spin_unlock(&bg->lock);
+
+		/*
+		 * Get out fast, in case we're read-only or unmounting the
+		 * filesystem. It is OK to drop block groups from the list even
+		 * for the read-only case. As we did sb_start_write(),
+		 * "mount -o remount,ro" won't happen and read-only filesystem
+		 * means it is forced read-only due to a fatal error. So, it
+		 * never gets back to read-write to let us reclaim again.
+		 */
+		if (btrfs_need_cleaner_sleep(fs_info)) {
+			up_write(&space_info->groups_sem);
+			goto next;
+		}
+
+		/*
+		 * Cache the zone_unusable value before turning the block group
+		 * to read only. As soon as the blog group is read only it's
+		 * zone_unusable value gets moved to the block group's read-only
+		 * bytes and isn't available for calculations anymore.
+		 */
+		zone_unusable = bg->zone_unusable;
+		ret = inc_block_group_ro(bg, 0);
+		up_write(&space_info->groups_sem);
+		if (ret < 0)
+			goto next;
+
+		btrfs_info(fs_info,
+			"reclaiming chunk %llu with %llu%% used %llu%% unusable",
+				bg->start,
+				div64_u64(bg->used * 100, bg->length),
+				div64_u64(zone_unusable * 100, bg->length));
+		trace_btrfs_reclaim_block_group(bg);
+		ret = btrfs_relocate_chunk(fs_info, bg->start);
+		if (ret) {
+			btrfs_dec_block_group_ro(bg);
+			btrfs_err(fs_info, "error relocating chunk %llu",
+				  bg->start);
+		}
+
+next:
+		if (ret)
+			btrfs_mark_bg_to_reclaim(bg);
+		btrfs_put_block_group(bg);
+
+		mutex_unlock(&fs_info->reclaim_bgs_lock);
+		/*
+		 * Reclaiming all the block groups in the list can take really
+		 * long.  Prioritize cleaning up unused block groups.
+		 */
+		btrfs_delete_unused_bgs(fs_info);
+		/*
+		 * If we are interrupted by a balance, we can just bail out. The
+		 * cleaner thread restart again if necessary.
+		 */
+		if (!mutex_trylock(&fs_info->reclaim_bgs_lock))
+			goto end;
+		spin_lock(&fs_info->unused_bgs_lock);
+	}
+	spin_unlock(&fs_info->unused_bgs_lock);
+	mutex_unlock(&fs_info->reclaim_bgs_lock);
+end:
+	btrfs_exclop_finish(fs_info);
+	sb_end_write(fs_info->sb);
+}
+
+void btrfs_reclaim_bgs(struct btrfs_fs_info *fs_info)
+{
+	spin_lock(&fs_info->unused_bgs_lock);
+	if (!list_empty(&fs_info->reclaim_bgs))
+		queue_work(system_unbound_wq, &fs_info->reclaim_bgs_work);
+	spin_unlock(&fs_info->unused_bgs_lock);
+}
+
+void btrfs_mark_bg_to_reclaim(struct btrfs_block_group *bg)
+{
+	struct btrfs_fs_info *fs_info = bg->fs_info;
+
+	spin_lock(&fs_info->unused_bgs_lock);
+	if (list_empty(&bg->bg_list)) {
+		btrfs_get_block_group(bg);
+		trace_btrfs_add_reclaim_block_group(bg);
+		list_add_tail(&bg->bg_list, &fs_info->reclaim_bgs);
+	}
+	spin_unlock(&fs_info->unused_bgs_lock);
+}
+
+static int read_bg_from_eb(struct btrfs_fs_info *fs_info, struct btrfs_key *key,
+			   struct btrfs_path *path)
+{
+	struct extent_map_tree *em_tree;
+	struct extent_map *em;
+	struct btrfs_block_group_item bg;
+	struct extent_buffer *leaf;
+	int slot;
+	u64 flags;
+	int ret = 0;
+
+	slot = path->slots[0];
+	leaf = path->nodes[0];
+
+	em_tree = &fs_info->mapping_tree;
+	read_lock(&em_tree->lock);
+	em = lookup_extent_mapping(em_tree, key->objectid, key->offset);
+	read_unlock(&em_tree->lock);
+	if (!em) {
+		btrfs_err(fs_info,
+			  "logical %llu len %llu found bg but no related chunk",
+			  key->objectid, key->offset);
+		return -ENOENT;
+	}
+
+	if (em->start != key->objectid || em->len != key->offset) {
+		btrfs_err(fs_info,
+			"block group %llu len %llu mismatch with chunk %llu len %llu",
+			key->objectid, key->offset, em->start, em->len);
+		ret = -EUCLEAN;
+		goto out_free_em;
+	}
+
+	read_extent_buffer(leaf, &bg, btrfs_item_ptr_offset(leaf, slot),
+			   sizeof(bg));
+	flags = btrfs_stack_block_group_flags(&bg) &
+		BTRFS_BLOCK_GROUP_TYPE_MASK;
+
+	if (flags != (em->map_lookup->type & BTRFS_BLOCK_GROUP_TYPE_MASK)) {
+		btrfs_err(fs_info,
+"block group %llu len %llu type flags 0x%llx mismatch with chunk type flags 0x%llx",
+			  key->objectid, key->offset, flags,
+			  (BTRFS_BLOCK_GROUP_TYPE_MASK & em->map_lookup->type));
+		ret = -EUCLEAN;
+	}
+
+out_free_em:
+	free_extent_map(em);
+	return ret;
+}
+
+static int find_first_block_group(struct btrfs_fs_info *fs_info,
+				  struct btrfs_path *path,
+				  struct btrfs_key *key)
+{
+	struct btrfs_root *root = btrfs_block_group_root(fs_info);
+	int ret;
+	struct btrfs_key found_key;
+
+	btrfs_for_each_slot(root, key, &found_key, path, ret) {
+		if (found_key.objectid >= key->objectid &&
+		    found_key.type == BTRFS_BLOCK_GROUP_ITEM_KEY) {
+			return read_bg_from_eb(fs_info, &found_key, path);
+		}
+	}
+	return ret;
+}
+
+static void set_avail_alloc_bits(struct btrfs_fs_info *fs_info, u64 flags)
+{
+	u64 extra_flags = chunk_to_extended(flags) &
+				BTRFS_EXTENDED_PROFILE_MASK;
+
+	write_seqlock(&fs_info->profiles_lock);
+	if (flags & BTRFS_BLOCK_GROUP_DATA)
+		fs_info->avail_data_alloc_bits |= extra_flags;
+	if (flags & BTRFS_BLOCK_GROUP_METADATA)
+		fs_info->avail_metadata_alloc_bits |= extra_flags;
+	if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
+		fs_info->avail_system_alloc_bits |= extra_flags;
+	write_sequnlock(&fs_info->profiles_lock);
+}
+
+/*
+ * Map a physical disk address to a list of logical addresses.
+ *
+ * @fs_info:       the filesystem
+ * @chunk_start:   logical address of block group
+ * @physical:	   physical address to map to logical addresses
+ * @logical:	   return array of logical addresses which map to @physical
+ * @naddrs:	   length of @logical
+ * @stripe_len:    size of IO stripe for the given block group
+ *
+ * Maps a particular @physical disk address to a list of @logical addresses.
+ * Used primarily to exclude those portions of a block group that contain super
+ * block copies.
+ */
+int btrfs_rmap_block(struct btrfs_fs_info *fs_info, u64 chunk_start,
+		     u64 physical, u64 **logical, int *naddrs, int *stripe_len)
+{
+	struct extent_map *em;
+	struct map_lookup *map;
+	u64 *buf;
+	u64 bytenr;
+	u64 data_stripe_length;
+	u64 io_stripe_size;
+	int i, nr = 0;
+	int ret = 0;
+
+	em = btrfs_get_chunk_map(fs_info, chunk_start, 1);
+	if (IS_ERR(em))
+		return -EIO;
+
+	map = em->map_lookup;
+	data_stripe_length = em->orig_block_len;
+	io_stripe_size = BTRFS_STRIPE_LEN;
+	chunk_start = em->start;
+
+	/* For RAID5/6 adjust to a full IO stripe length */
+	if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK)
+		io_stripe_size = btrfs_stripe_nr_to_offset(nr_data_stripes(map));
+
+	buf = kcalloc(map->num_stripes, sizeof(u64), GFP_NOFS);
+	if (!buf) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	for (i = 0; i < map->num_stripes; i++) {
+		bool already_inserted = false;
+		u32 stripe_nr;
+		u32 offset;
+		int j;
+
+		if (!in_range(physical, map->stripes[i].physical,
+			      data_stripe_length))
+			continue;
+
+		stripe_nr = (physical - map->stripes[i].physical) >>
+			    BTRFS_STRIPE_LEN_SHIFT;
+		offset = (physical - map->stripes[i].physical) &
+			 BTRFS_STRIPE_LEN_MASK;
+
+		if (map->type & (BTRFS_BLOCK_GROUP_RAID0 |
+				 BTRFS_BLOCK_GROUP_RAID10))
+			stripe_nr = div_u64(stripe_nr * map->num_stripes + i,
+					    map->sub_stripes);
+		/*
+		 * The remaining case would be for RAID56, multiply by
+		 * nr_data_stripes().  Alternatively, just use rmap_len below
+		 * instead of map->stripe_len
+		 */
+		bytenr = chunk_start + stripe_nr * io_stripe_size + offset;
+
+		/* Ensure we don't add duplicate addresses */
+		for (j = 0; j < nr; j++) {
+			if (buf[j] == bytenr) {
+				already_inserted = true;
+				break;
+			}
+		}
+
+		if (!already_inserted)
+			buf[nr++] = bytenr;
+	}
+
+	*logical = buf;
+	*naddrs = nr;
+	*stripe_len = io_stripe_size;
+out:
+	free_extent_map(em);
+	return ret;
+}
+
+static int exclude_super_stripes(struct btrfs_block_group *cache)
+{
+	struct btrfs_fs_info *fs_info = cache->fs_info;
+	const bool zoned = btrfs_is_zoned(fs_info);
+	u64 bytenr;
+	u64 *logical;
+	int stripe_len;
+	int i, nr, ret;
+
+	if (cache->start < BTRFS_SUPER_INFO_OFFSET) {
+		stripe_len = BTRFS_SUPER_INFO_OFFSET - cache->start;
+		cache->bytes_super += stripe_len;
+		ret = set_extent_bit(&fs_info->excluded_extents, cache->start,
+				     cache->start + stripe_len - 1,
+				     EXTENT_UPTODATE, NULL);
+		if (ret)
+			return ret;
+	}
+
+	for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
+		bytenr = btrfs_sb_offset(i);
+		ret = btrfs_rmap_block(fs_info, cache->start,
+				       bytenr, &logical, &nr, &stripe_len);
+		if (ret)
+			return ret;
+
+		/* Shouldn't have super stripes in sequential zones */
+		if (zoned && nr) {
+			kfree(logical);
+			btrfs_err(fs_info,
+			"zoned: block group %llu must not contain super block",
+				  cache->start);
+			return -EUCLEAN;
+		}
+
+		while (nr--) {
+			u64 len = min_t(u64, stripe_len,
+				cache->start + cache->length - logical[nr]);
+
+			cache->bytes_super += len;
+			ret = set_extent_bit(&fs_info->excluded_extents, logical[nr],
+					     logical[nr] + len - 1,
+					     EXTENT_UPTODATE, NULL);
+			if (ret) {
+				kfree(logical);
+				return ret;
+			}
+		}
+
+		kfree(logical);
+	}
+	return 0;
+}
+
+static struct btrfs_block_group *btrfs_create_block_group_cache(
+		struct btrfs_fs_info *fs_info, u64 start)
+{
+	struct btrfs_block_group *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->start = start;
+
+	cache->fs_info = fs_info;
+	cache->full_stripe_len = btrfs_full_stripe_len(fs_info, start);
+
+	cache->discard_index = BTRFS_DISCARD_INDEX_UNUSED;
+
+	refcount_set(&cache->refs, 1);
+	spin_lock_init(&cache->lock);
+	init_rwsem(&cache->data_rwsem);
+	INIT_LIST_HEAD(&cache->list);
+	INIT_LIST_HEAD(&cache->cluster_list);
+	INIT_LIST_HEAD(&cache->bg_list);
+	INIT_LIST_HEAD(&cache->ro_list);
+	INIT_LIST_HEAD(&cache->discard_list);
+	INIT_LIST_HEAD(&cache->dirty_list);
+	INIT_LIST_HEAD(&cache->io_list);
+	INIT_LIST_HEAD(&cache->active_bg_list);
+	btrfs_init_free_space_ctl(cache, cache->free_space_ctl);
+	atomic_set(&cache->frozen, 0);
+	mutex_init(&cache->free_space_lock);
+
+	return cache;
+}
+
+/*
+ * Iterate all chunks and verify that each of them has the corresponding block
+ * group
+ */
+static int check_chunk_block_group_mappings(struct btrfs_fs_info *fs_info)
+{
+	struct extent_map_tree *map_tree = &fs_info->mapping_tree;
+	struct extent_map *em;
+	struct btrfs_block_group *bg;
+	u64 start = 0;
+	int ret = 0;
+
+	while (1) {
+		read_lock(&map_tree->lock);
+		/*
+		 * lookup_extent_mapping will return the first extent map
+		 * intersecting the range, so setting @len to 1 is enough to
+		 * get the first chunk.
+		 */
+		em = lookup_extent_mapping(map_tree, start, 1);
+		read_unlock(&map_tree->lock);
+		if (!em)
+			break;
+
+		bg = btrfs_lookup_block_group(fs_info, em->start);
+		if (!bg) {
+			btrfs_err(fs_info,
+	"chunk start=%llu len=%llu doesn't have corresponding block group",
+				     em->start, em->len);
+			ret = -EUCLEAN;
+			free_extent_map(em);
+			break;
+		}
+		if (bg->start != em->start || bg->length != em->len ||
+		    (bg->flags & BTRFS_BLOCK_GROUP_TYPE_MASK) !=
+		    (em->map_lookup->type & BTRFS_BLOCK_GROUP_TYPE_MASK)) {
+			btrfs_err(fs_info,
+"chunk start=%llu len=%llu flags=0x%llx doesn't match block group start=%llu len=%llu flags=0x%llx",
+				em->start, em->len,
+				em->map_lookup->type & BTRFS_BLOCK_GROUP_TYPE_MASK,
+				bg->start, bg->length,
+				bg->flags & BTRFS_BLOCK_GROUP_TYPE_MASK);
+			ret = -EUCLEAN;
+			free_extent_map(em);
+			btrfs_put_block_group(bg);
+			break;
+		}
+		start = em->start + em->len;
+		free_extent_map(em);
+		btrfs_put_block_group(bg);
+	}
+	return ret;
+}
+
+static int read_one_block_group(struct btrfs_fs_info *info,
+				struct btrfs_block_group_item *bgi,
+				const struct btrfs_key *key,
+				int need_clear)
+{
+	struct btrfs_block_group *cache;
+	const bool mixed = btrfs_fs_incompat(info, MIXED_GROUPS);
+	int ret;
+
+	ASSERT(key->type == BTRFS_BLOCK_GROUP_ITEM_KEY);
+
+	cache = btrfs_create_block_group_cache(info, key->objectid);
+	if (!cache)
+		return -ENOMEM;
+
+	cache->length = key->offset;
+	cache->used = btrfs_stack_block_group_used(bgi);
+	cache->commit_used = cache->used;
+	cache->flags = btrfs_stack_block_group_flags(bgi);
+	cache->global_root_id = btrfs_stack_block_group_chunk_objectid(bgi);
+
+	set_free_space_tree_thresholds(cache);
+
+	if (need_clear) {
+		/*
+		 * When we mount with old space cache, we need to
+		 * set BTRFS_DC_CLEAR and set dirty flag.
+		 *
+		 * a) Setting 'BTRFS_DC_CLEAR' makes sure that we
+		 *    truncate the old free space cache inode and
+		 *    setup a new one.
+		 * b) Setting 'dirty flag' makes sure that we flush
+		 *    the new space cache info onto disk.
+		 */
+		if (btrfs_test_opt(info, SPACE_CACHE))
+			cache->disk_cache_state = BTRFS_DC_CLEAR;
+	}
+	if (!mixed && ((cache->flags & BTRFS_BLOCK_GROUP_METADATA) &&
+	    (cache->flags & BTRFS_BLOCK_GROUP_DATA))) {
+			btrfs_err(info,
+"bg %llu is a mixed block group but filesystem hasn't enabled mixed block groups",
+				  cache->start);
+			ret = -EINVAL;
+			goto error;
+	}
+
+	ret = btrfs_load_block_group_zone_info(cache, false);
+	if (ret) {
+		btrfs_err(info, "zoned: failed to load zone info of bg %llu",
+			  cache->start);
+		goto error;
+	}
+
+	/*
+	 * We need to exclude the super stripes now so that the space info has
+	 * super bytes accounted for, otherwise we'll think we have more space
+	 * than we actually do.
+	 */
+	ret = exclude_super_stripes(cache);
+	if (ret) {
+		/* We may have excluded something, so call this just in case. */
+		btrfs_free_excluded_extents(cache);
+		goto error;
+	}
+
+	/*
+	 * For zoned filesystem, space after the allocation offset is the only
+	 * free space for a block group. So, we don't need any caching work.
+	 * btrfs_calc_zone_unusable() will set the amount of free space and
+	 * zone_unusable space.
+	 *
+	 * For regular filesystem, check for two cases, either we are full, and
+	 * therefore don't need to bother with the caching work since we won't
+	 * find any space, or we are empty, and we can just add all the space
+	 * in and be done with it.  This saves us _a_lot_ of time, particularly
+	 * in the full case.
+	 */
+	if (btrfs_is_zoned(info)) {
+		btrfs_calc_zone_unusable(cache);
+		/* Should not have any excluded extents. Just in case, though. */
+		btrfs_free_excluded_extents(cache);
+	} else if (cache->length == cache->used) {
+		cache->cached = BTRFS_CACHE_FINISHED;
+		btrfs_free_excluded_extents(cache);
+	} else if (cache->used == 0) {
+		cache->cached = BTRFS_CACHE_FINISHED;
+		ret = btrfs_add_new_free_space(cache, cache->start,
+					       cache->start + cache->length, NULL);
+		btrfs_free_excluded_extents(cache);
+		if (ret)
+			goto error;
+	}
+
+	ret = btrfs_add_block_group_cache(info, cache);
+	if (ret) {
+		btrfs_remove_free_space_cache(cache);
+		goto error;
+	}
+	trace_btrfs_add_block_group(info, cache, 0);
+	btrfs_add_bg_to_space_info(info, cache);
+
+	set_avail_alloc_bits(info, cache->flags);
+	if (btrfs_chunk_writeable(info, cache->start)) {
+		if (cache->used == 0) {
+			ASSERT(list_empty(&cache->bg_list));
+			if (btrfs_test_opt(info, DISCARD_ASYNC))
+				btrfs_discard_queue_work(&info->discard_ctl, cache);
+			else
+				btrfs_mark_bg_unused(cache);
+		}
+	} else {
+		inc_block_group_ro(cache, 1);
+	}
+
+	return 0;
+error:
+	btrfs_put_block_group(cache);
+	return ret;
+}
+
+static int fill_dummy_bgs(struct btrfs_fs_info *fs_info)
+{
+	struct extent_map_tree *em_tree = &fs_info->mapping_tree;
+	struct rb_node *node;
+	int ret = 0;
+
+	for (node = rb_first_cached(&em_tree->map); node; node = rb_next(node)) {
+		struct extent_map *em;
+		struct map_lookup *map;
+		struct btrfs_block_group *bg;
+
+		em = rb_entry(node, struct extent_map, rb_node);
+		map = em->map_lookup;
+		bg = btrfs_create_block_group_cache(fs_info, em->start);
+		if (!bg) {
+			ret = -ENOMEM;
+			break;
+		}
+
+		/* Fill dummy cache as FULL */
+		bg->length = em->len;
+		bg->flags = map->type;
+		bg->cached = BTRFS_CACHE_FINISHED;
+		bg->used = em->len;
+		bg->flags = map->type;
+		ret = btrfs_add_block_group_cache(fs_info, bg);
+		/*
+		 * We may have some valid block group cache added already, in
+		 * that case we skip to the next one.
+		 */
+		if (ret == -EEXIST) {
+			ret = 0;
+			btrfs_put_block_group(bg);
+			continue;
+		}
+
+		if (ret) {
+			btrfs_remove_free_space_cache(bg);
+			btrfs_put_block_group(bg);
+			break;
+		}
+
+		btrfs_add_bg_to_space_info(fs_info, bg);
+
+		set_avail_alloc_bits(fs_info, bg->flags);
+	}
+	if (!ret)
+		btrfs_init_global_block_rsv(fs_info);
+	return ret;
+}
+
+int btrfs_read_block_groups(struct btrfs_fs_info *info)
+{
+	struct btrfs_root *root = btrfs_block_group_root(info);
+	struct btrfs_path *path;
+	int ret;
+	struct btrfs_block_group *cache;
+	struct btrfs_space_info *space_info;
+	struct btrfs_key key;
+	int need_clear = 0;
+	u64 cache_gen;
+
+	/*
+	 * Either no extent root (with ibadroots rescue option) or we have
+	 * unsupported RO options. The fs can never be mounted read-write, so no
+	 * need to waste time searching block group items.
+	 *
+	 * This also allows new extent tree related changes to be RO compat,
+	 * no need for a full incompat flag.
+	 */
+	if (!root || (btrfs_super_compat_ro_flags(info->super_copy) &
+		      ~BTRFS_FEATURE_COMPAT_RO_SUPP))
+		return fill_dummy_bgs(info);
+
+	key.objectid = 0;
+	key.offset = 0;
+	key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	cache_gen = btrfs_super_cache_generation(info->super_copy);
+	if (btrfs_test_opt(info, SPACE_CACHE) &&
+	    btrfs_super_generation(info->super_copy) != cache_gen)
+		need_clear = 1;
+	if (btrfs_test_opt(info, CLEAR_CACHE))
+		need_clear = 1;
+
+	while (1) {
+		struct btrfs_block_group_item bgi;
+		struct extent_buffer *leaf;
+		int slot;
+
+		ret = find_first_block_group(info, path, &key);
+		if (ret > 0)
+			break;
+		if (ret != 0)
+			goto error;
+
+		leaf = path->nodes[0];
+		slot = path->slots[0];
+
+		read_extent_buffer(leaf, &bgi, btrfs_item_ptr_offset(leaf, slot),
+				   sizeof(bgi));
+
+		btrfs_item_key_to_cpu(leaf, &key, slot);
+		btrfs_release_path(path);
+		ret = read_one_block_group(info, &bgi, &key, need_clear);
+		if (ret < 0)
+			goto error;
+		key.objectid += key.offset;
+		key.offset = 0;
+	}
+	btrfs_release_path(path);
+
+	list_for_each_entry(space_info, &info->space_info, list) {
+		int i;
+
+		for (i = 0; i < BTRFS_NR_RAID_TYPES; i++) {
+			if (list_empty(&space_info->block_groups[i]))
+				continue;
+			cache = list_first_entry(&space_info->block_groups[i],
+						 struct btrfs_block_group,
+						 list);
+			btrfs_sysfs_add_block_group_type(cache);
+		}
+
+		if (!(btrfs_get_alloc_profile(info, space_info->flags) &
+		      (BTRFS_BLOCK_GROUP_RAID10 |
+		       BTRFS_BLOCK_GROUP_RAID1_MASK |
+		       BTRFS_BLOCK_GROUP_RAID56_MASK |
+		       BTRFS_BLOCK_GROUP_DUP)))
+			continue;
+		/*
+		 * Avoid allocating from un-mirrored block group if there are
+		 * mirrored block groups.
+		 */
+		list_for_each_entry(cache,
+				&space_info->block_groups[BTRFS_RAID_RAID0],
+				list)
+			inc_block_group_ro(cache, 1);
+		list_for_each_entry(cache,
+				&space_info->block_groups[BTRFS_RAID_SINGLE],
+				list)
+			inc_block_group_ro(cache, 1);
+	}
+
+	btrfs_init_global_block_rsv(info);
+	ret = check_chunk_block_group_mappings(info);
+error:
+	btrfs_free_path(path);
+	/*
+	 * We've hit some error while reading the extent tree, and have
+	 * rescue=ibadroots mount option.
+	 * Try to fill the tree using dummy block groups so that the user can
+	 * continue to mount and grab their data.
+	 */
+	if (ret && btrfs_test_opt(info, IGNOREBADROOTS))
+		ret = fill_dummy_bgs(info);
+	return ret;
+}
+
+/*
+ * This function, insert_block_group_item(), belongs to the phase 2 of chunk
+ * allocation.
+ *
+ * See the comment at btrfs_chunk_alloc() for details about the chunk allocation
+ * phases.
+ */
+static int insert_block_group_item(struct btrfs_trans_handle *trans,
+				   struct btrfs_block_group *block_group)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_block_group_item bgi;
+	struct btrfs_root *root = btrfs_block_group_root(fs_info);
+	struct btrfs_key key;
+	u64 old_commit_used;
+	int ret;
+
+	spin_lock(&block_group->lock);
+	btrfs_set_stack_block_group_used(&bgi, block_group->used);
+	btrfs_set_stack_block_group_chunk_objectid(&bgi,
+						   block_group->global_root_id);
+	btrfs_set_stack_block_group_flags(&bgi, block_group->flags);
+	old_commit_used = block_group->commit_used;
+	block_group->commit_used = block_group->used;
+	key.objectid = block_group->start;
+	key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
+	key.offset = block_group->length;
+	spin_unlock(&block_group->lock);
+
+	ret = btrfs_insert_item(trans, root, &key, &bgi, sizeof(bgi));
+	if (ret < 0) {
+		spin_lock(&block_group->lock);
+		block_group->commit_used = old_commit_used;
+		spin_unlock(&block_group->lock);
+	}
+
+	return ret;
+}
+
+static int insert_dev_extent(struct btrfs_trans_handle *trans,
+			    struct btrfs_device *device, u64 chunk_offset,
+			    u64 start, u64 num_bytes)
+{
+	struct btrfs_fs_info *fs_info = device->fs_info;
+	struct btrfs_root *root = fs_info->dev_root;
+	struct btrfs_path *path;
+	struct btrfs_dev_extent *extent;
+	struct extent_buffer *leaf;
+	struct btrfs_key key;
+	int ret;
+
+	WARN_ON(!test_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state));
+	WARN_ON(test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state));
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	key.objectid = device->devid;
+	key.type = BTRFS_DEV_EXTENT_KEY;
+	key.offset = start;
+	ret = btrfs_insert_empty_item(trans, root, path, &key, sizeof(*extent));
+	if (ret)
+		goto out;
+
+	leaf = path->nodes[0];
+	extent = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_dev_extent);
+	btrfs_set_dev_extent_chunk_tree(leaf, extent, BTRFS_CHUNK_TREE_OBJECTID);
+	btrfs_set_dev_extent_chunk_objectid(leaf, extent,
+					    BTRFS_FIRST_CHUNK_TREE_OBJECTID);
+	btrfs_set_dev_extent_chunk_offset(leaf, extent, chunk_offset);
+
+	btrfs_set_dev_extent_length(leaf, extent, num_bytes);
+	btrfs_mark_buffer_dirty(trans, leaf);
+out:
+	btrfs_free_path(path);
+	return ret;
+}
+
+/*
+ * This function belongs to phase 2.
+ *
+ * See the comment at btrfs_chunk_alloc() for details about the chunk allocation
+ * phases.
+ */
+static int insert_dev_extents(struct btrfs_trans_handle *trans,
+				   u64 chunk_offset, u64 chunk_size)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_device *device;
+	struct extent_map *em;
+	struct map_lookup *map;
+	u64 dev_offset;
+	u64 stripe_size;
+	int i;
+	int ret = 0;
+
+	em = btrfs_get_chunk_map(fs_info, chunk_offset, chunk_size);
+	if (IS_ERR(em))
+		return PTR_ERR(em);
+
+	map = em->map_lookup;
+	stripe_size = em->orig_block_len;
+
+	/*
+	 * Take the device list mutex to prevent races with the final phase of
+	 * a device replace operation that replaces the device object associated
+	 * with the map's stripes, because the device object's id can change
+	 * at any time during that final phase of the device replace operation
+	 * (dev-replace.c:btrfs_dev_replace_finishing()), so we could grab the
+	 * replaced device and then see it with an ID of BTRFS_DEV_REPLACE_DEVID,
+	 * resulting in persisting a device extent item with such ID.
+	 */
+	mutex_lock(&fs_info->fs_devices->device_list_mutex);
+	for (i = 0; i < map->num_stripes; i++) {
+		device = map->stripes[i].dev;
+		dev_offset = map->stripes[i].physical;
+
+		ret = insert_dev_extent(trans, device, chunk_offset, dev_offset,
+				       stripe_size);
+		if (ret)
+			break;
+	}
+	mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+
+	free_extent_map(em);
+	return ret;
+}
+
+/*
+ * This function, btrfs_create_pending_block_groups(), belongs to the phase 2 of
+ * chunk allocation.
+ *
+ * See the comment at btrfs_chunk_alloc() for details about the chunk allocation
+ * phases.
+ */
+void btrfs_create_pending_block_groups(struct btrfs_trans_handle *trans)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_block_group *block_group;
+	int ret = 0;
+
+	while (!list_empty(&trans->new_bgs)) {
+		int index;
+
+		block_group = list_first_entry(&trans->new_bgs,
+					       struct btrfs_block_group,
+					       bg_list);
+		if (ret)
+			goto next;
+
+		index = btrfs_bg_flags_to_raid_index(block_group->flags);
+
+		ret = insert_block_group_item(trans, block_group);
+		if (ret)
+			btrfs_abort_transaction(trans, ret);
+		if (!test_bit(BLOCK_GROUP_FLAG_CHUNK_ITEM_INSERTED,
+			      &block_group->runtime_flags)) {
+			mutex_lock(&fs_info->chunk_mutex);
+			ret = btrfs_chunk_alloc_add_chunk_item(trans, block_group);
+			mutex_unlock(&fs_info->chunk_mutex);
+			if (ret)
+				btrfs_abort_transaction(trans, ret);
+		}
+		ret = insert_dev_extents(trans, block_group->start,
+					 block_group->length);
+		if (ret)
+			btrfs_abort_transaction(trans, ret);
+		add_block_group_free_space(trans, block_group);
+
+		/*
+		 * If we restriped during balance, we may have added a new raid
+		 * type, so now add the sysfs entries when it is safe to do so.
+		 * We don't have to worry about locking here as it's handled in
+		 * btrfs_sysfs_add_block_group_type.
+		 */
+		if (block_group->space_info->block_group_kobjs[index] == NULL)
+			btrfs_sysfs_add_block_group_type(block_group);
+
+		/* Already aborted the transaction if it failed. */
+next:
+		btrfs_delayed_refs_rsv_release(fs_info, 1);
+		list_del_init(&block_group->bg_list);
+		clear_bit(BLOCK_GROUP_FLAG_NEW, &block_group->runtime_flags);
+	}
+	btrfs_trans_release_chunk_metadata(trans);
+}
+
+/*
+ * For extent tree v2 we use the block_group_item->chunk_offset to point at our
+ * global root id.  For v1 it's always set to BTRFS_FIRST_CHUNK_TREE_OBJECTID.
+ */
+static u64 calculate_global_root_id(struct btrfs_fs_info *fs_info, u64 offset)
+{
+	u64 div = SZ_1G;
+	u64 index;
+
+	if (!btrfs_fs_incompat(fs_info, EXTENT_TREE_V2))
+		return BTRFS_FIRST_CHUNK_TREE_OBJECTID;
+
+	/* If we have a smaller fs index based on 128MiB. */
+	if (btrfs_super_total_bytes(fs_info->super_copy) <= (SZ_1G * 10ULL))
+		div = SZ_128M;
+
+	offset = div64_u64(offset, div);
+	div64_u64_rem(offset, fs_info->nr_global_roots, &index);
+	return index;
+}
+
+struct btrfs_block_group *btrfs_make_block_group(struct btrfs_trans_handle *trans,
+						 u64 type,
+						 u64 chunk_offset, u64 size)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_block_group *cache;
+	int ret;
+
+	btrfs_set_log_full_commit(trans);
+
+	cache = btrfs_create_block_group_cache(fs_info, chunk_offset);
+	if (!cache)
+		return ERR_PTR(-ENOMEM);
+
+	/*
+	 * Mark it as new before adding it to the rbtree of block groups or any
+	 * list, so that no other task finds it and calls btrfs_mark_bg_unused()
+	 * before the new flag is set.
+	 */
+	set_bit(BLOCK_GROUP_FLAG_NEW, &cache->runtime_flags);
+
+	cache->length = size;
+	set_free_space_tree_thresholds(cache);
+	cache->flags = type;
+	cache->cached = BTRFS_CACHE_FINISHED;
+	cache->global_root_id = calculate_global_root_id(fs_info, cache->start);
+
+	if (btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE))
+		set_bit(BLOCK_GROUP_FLAG_NEEDS_FREE_SPACE, &cache->runtime_flags);
+
+	ret = btrfs_load_block_group_zone_info(cache, true);
+	if (ret) {
+		btrfs_put_block_group(cache);
+		return ERR_PTR(ret);
+	}
+
+	ret = exclude_super_stripes(cache);
+	if (ret) {
+		/* We may have excluded something, so call this just in case */
+		btrfs_free_excluded_extents(cache);
+		btrfs_put_block_group(cache);
+		return ERR_PTR(ret);
+	}
+
+	ret = btrfs_add_new_free_space(cache, chunk_offset, chunk_offset + size, NULL);
+	btrfs_free_excluded_extents(cache);
+	if (ret) {
+		btrfs_put_block_group(cache);
+		return ERR_PTR(ret);
+	}
+
+	/*
+	 * Ensure the corresponding space_info object is created and
+	 * assigned to our block group. We want our bg to be added to the rbtree
+	 * with its ->space_info set.
+	 */
+	cache->space_info = btrfs_find_space_info(fs_info, cache->flags);
+	ASSERT(cache->space_info);
+
+	ret = btrfs_add_block_group_cache(fs_info, cache);
+	if (ret) {
+		btrfs_remove_free_space_cache(cache);
+		btrfs_put_block_group(cache);
+		return ERR_PTR(ret);
+	}
+
+	/*
+	 * Now that our block group has its ->space_info set and is inserted in
+	 * the rbtree, update the space info's counters.
+	 */
+	trace_btrfs_add_block_group(fs_info, cache, 1);
+	btrfs_add_bg_to_space_info(fs_info, cache);
+	btrfs_update_global_block_rsv(fs_info);
+
+#ifdef CONFIG_BTRFS_DEBUG
+	if (btrfs_should_fragment_free_space(cache)) {
+		cache->space_info->bytes_used += size >> 1;
+		fragment_free_space(cache);
+	}
+#endif
+
+	list_add_tail(&cache->bg_list, &trans->new_bgs);
+	trans->delayed_ref_updates++;
+	btrfs_update_delayed_refs_rsv(trans);
+
+	set_avail_alloc_bits(fs_info, type);
+	return cache;
+}
+
+/*
+ * Mark one block group RO, can be called several times for the same block
+ * group.
+ *
+ * @cache:		the destination block group
+ * @do_chunk_alloc:	whether need to do chunk pre-allocation, this is to
+ * 			ensure we still have some free space after marking this
+ * 			block group RO.
+ */
+int btrfs_inc_block_group_ro(struct btrfs_block_group *cache,
+			     bool do_chunk_alloc)
+{
+	struct btrfs_fs_info *fs_info = cache->fs_info;
+	struct btrfs_trans_handle *trans;
+	struct btrfs_root *root = btrfs_block_group_root(fs_info);
+	u64 alloc_flags;
+	int ret;
+	bool dirty_bg_running;
+
+	/*
+	 * This can only happen when we are doing read-only scrub on read-only
+	 * mount.
+	 * In that case we should not start a new transaction on read-only fs.
+	 * Thus here we skip all chunk allocations.
+	 */
+	if (sb_rdonly(fs_info->sb)) {
+		mutex_lock(&fs_info->ro_block_group_mutex);
+		ret = inc_block_group_ro(cache, 0);
+		mutex_unlock(&fs_info->ro_block_group_mutex);
+		return ret;
+	}
+
+	do {
+		trans = btrfs_join_transaction(root);
+		if (IS_ERR(trans))
+			return PTR_ERR(trans);
+
+		dirty_bg_running = false;
+
+		/*
+		 * We're not allowed to set block groups readonly after the dirty
+		 * block group cache has started writing.  If it already started,
+		 * back off and let this transaction commit.
+		 */
+		mutex_lock(&fs_info->ro_block_group_mutex);
+		if (test_bit(BTRFS_TRANS_DIRTY_BG_RUN, &trans->transaction->flags)) {
+			u64 transid = trans->transid;
+
+			mutex_unlock(&fs_info->ro_block_group_mutex);
+			btrfs_end_transaction(trans);
+
+			ret = btrfs_wait_for_commit(fs_info, transid);
+			if (ret)
+				return ret;
+			dirty_bg_running = true;
+		}
+	} while (dirty_bg_running);
+
+	if (do_chunk_alloc) {
+		/*
+		 * If we are changing raid levels, try to allocate a
+		 * corresponding block group with the new raid level.
+		 */
+		alloc_flags = btrfs_get_alloc_profile(fs_info, cache->flags);
+		if (alloc_flags != cache->flags) {
+			ret = btrfs_chunk_alloc(trans, alloc_flags,
+						CHUNK_ALLOC_FORCE);
+			/*
+			 * ENOSPC is allowed here, we may have enough space
+			 * already allocated at the new raid level to carry on
+			 */
+			if (ret == -ENOSPC)
+				ret = 0;
+			if (ret < 0)
+				goto out;
+		}
+	}
+
+	ret = inc_block_group_ro(cache, 0);
+	if (!ret)
+		goto out;
+	if (ret == -ETXTBSY)
+		goto unlock_out;
+
+	/*
+	 * Skip chunk alloction if the bg is SYSTEM, this is to avoid system
+	 * chunk allocation storm to exhaust the system chunk array.  Otherwise
+	 * we still want to try our best to mark the block group read-only.
+	 */
+	if (!do_chunk_alloc && ret == -ENOSPC &&
+	    (cache->flags & BTRFS_BLOCK_GROUP_SYSTEM))
+		goto unlock_out;
+
+	alloc_flags = btrfs_get_alloc_profile(fs_info, cache->space_info->flags);
+	ret = btrfs_chunk_alloc(trans, alloc_flags, CHUNK_ALLOC_FORCE);
+	if (ret < 0)
+		goto out;
+	/*
+	 * We have allocated a new chunk. We also need to activate that chunk to
+	 * grant metadata tickets for zoned filesystem.
+	 */
+	ret = btrfs_zoned_activate_one_bg(fs_info, cache->space_info, true);
+	if (ret < 0)
+		goto out;
+
+	ret = inc_block_group_ro(cache, 0);
+	if (ret == -ETXTBSY)
+		goto unlock_out;
+out:
+	if (cache->flags & BTRFS_BLOCK_GROUP_SYSTEM) {
+		alloc_flags = btrfs_get_alloc_profile(fs_info, cache->flags);
+		mutex_lock(&fs_info->chunk_mutex);
+		check_system_chunk(trans, alloc_flags);
+		mutex_unlock(&fs_info->chunk_mutex);
+	}
+unlock_out:
+	mutex_unlock(&fs_info->ro_block_group_mutex);
+
+	btrfs_end_transaction(trans);
+	return ret;
+}
+
+void btrfs_dec_block_group_ro(struct btrfs_block_group *cache)
+{
+	struct btrfs_space_info *sinfo = cache->space_info;
+	u64 num_bytes;
+
+	BUG_ON(!cache->ro);
+
+	spin_lock(&sinfo->lock);
+	spin_lock(&cache->lock);
+	if (!--cache->ro) {
+		if (btrfs_is_zoned(cache->fs_info)) {
+			/* Migrate zone_unusable bytes back */
+			cache->zone_unusable =
+				(cache->alloc_offset - cache->used) +
+				(cache->length - cache->zone_capacity);
+			sinfo->bytes_zone_unusable += cache->zone_unusable;
+			sinfo->bytes_readonly -= cache->zone_unusable;
+		}
+		num_bytes = cache->length - cache->reserved -
+			    cache->pinned - cache->bytes_super -
+			    cache->zone_unusable - cache->used;
+		sinfo->bytes_readonly -= num_bytes;
+		list_del_init(&cache->ro_list);
+	}
+	spin_unlock(&cache->lock);
+	spin_unlock(&sinfo->lock);
+}
+
+static int update_block_group_item(struct btrfs_trans_handle *trans,
+				   struct btrfs_path *path,
+				   struct btrfs_block_group *cache)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	int ret;
+	struct btrfs_root *root = btrfs_block_group_root(fs_info);
+	unsigned long bi;
+	struct extent_buffer *leaf;
+	struct btrfs_block_group_item bgi;
+	struct btrfs_key key;
+	u64 old_commit_used;
+	u64 used;
+
+	/*
+	 * Block group items update can be triggered out of commit transaction
+	 * critical section, thus we need a consistent view of used bytes.
+	 * We cannot use cache->used directly outside of the spin lock, as it
+	 * may be changed.
+	 */
+	spin_lock(&cache->lock);
+	old_commit_used = cache->commit_used;
+	used = cache->used;
+	/* No change in used bytes, can safely skip it. */
+	if (cache->commit_used == used) {
+		spin_unlock(&cache->lock);
+		return 0;
+	}
+	cache->commit_used = used;
+	spin_unlock(&cache->lock);
+
+	key.objectid = cache->start;
+	key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
+	key.offset = cache->length;
+
+	ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
+	if (ret) {
+		if (ret > 0)
+			ret = -ENOENT;
+		goto fail;
+	}
+
+	leaf = path->nodes[0];
+	bi = btrfs_item_ptr_offset(leaf, path->slots[0]);
+	btrfs_set_stack_block_group_used(&bgi, used);
+	btrfs_set_stack_block_group_chunk_objectid(&bgi,
+						   cache->global_root_id);
+	btrfs_set_stack_block_group_flags(&bgi, cache->flags);
+	write_extent_buffer(leaf, &bgi, bi, sizeof(bgi));
+	btrfs_mark_buffer_dirty(trans, leaf);
+fail:
+	btrfs_release_path(path);
+	/*
+	 * We didn't update the block group item, need to revert commit_used
+	 * unless the block group item didn't exist yet - this is to prevent a
+	 * race with a concurrent insertion of the block group item, with
+	 * insert_block_group_item(), that happened just after we attempted to
+	 * update. In that case we would reset commit_used to 0 just after the
+	 * insertion set it to a value greater than 0 - if the block group later
+	 * becomes with 0 used bytes, we would incorrectly skip its update.
+	 */
+	if (ret < 0 && ret != -ENOENT) {
+		spin_lock(&cache->lock);
+		cache->commit_used = old_commit_used;
+		spin_unlock(&cache->lock);
+	}
+	return ret;
+
+}
+
+static int cache_save_setup(struct btrfs_block_group *block_group,
+			    struct btrfs_trans_handle *trans,
+			    struct btrfs_path *path)
+{
+	struct btrfs_fs_info *fs_info = block_group->fs_info;
+	struct btrfs_root *root = fs_info->tree_root;
+	struct inode *inode = NULL;
+	struct extent_changeset *data_reserved = NULL;
+	u64 alloc_hint = 0;
+	int dcs = BTRFS_DC_ERROR;
+	u64 cache_size = 0;
+	int retries = 0;
+	int ret = 0;
+
+	if (!btrfs_test_opt(fs_info, SPACE_CACHE))
+		return 0;
+
+	/*
+	 * If this block group is smaller than 100 megs don't bother caching the
+	 * block group.
+	 */
+	if (block_group->length < (100 * SZ_1M)) {
+		spin_lock(&block_group->lock);
+		block_group->disk_cache_state = BTRFS_DC_WRITTEN;
+		spin_unlock(&block_group->lock);
+		return 0;
+	}
+
+	if (TRANS_ABORTED(trans))
+		return 0;
+again:
+	inode = lookup_free_space_inode(block_group, path);
+	if (IS_ERR(inode) && PTR_ERR(inode) != -ENOENT) {
+		ret = PTR_ERR(inode);
+		btrfs_release_path(path);
+		goto out;
+	}
+
+	if (IS_ERR(inode)) {
+		BUG_ON(retries);
+		retries++;
+
+		if (block_group->ro)
+			goto out_free;
+
+		ret = create_free_space_inode(trans, block_group, path);
+		if (ret)
+			goto out_free;
+		goto again;
+	}
+
+	/*
+	 * We want to set the generation to 0, that way if anything goes wrong
+	 * from here on out we know not to trust this cache when we load up next
+	 * time.
+	 */
+	BTRFS_I(inode)->generation = 0;
+	ret = btrfs_update_inode(trans, root, BTRFS_I(inode));
+	if (ret) {
+		/*
+		 * So theoretically we could recover from this, simply set the
+		 * super cache generation to 0 so we know to invalidate the
+		 * cache, but then we'd have to keep track of the block groups
+		 * that fail this way so we know we _have_ to reset this cache
+		 * before the next commit or risk reading stale cache.  So to
+		 * limit our exposure to horrible edge cases lets just abort the
+		 * transaction, this only happens in really bad situations
+		 * anyway.
+		 */
+		btrfs_abort_transaction(trans, ret);
+		goto out_put;
+	}
+	WARN_ON(ret);
+
+	/* We've already setup this transaction, go ahead and exit */
+	if (block_group->cache_generation == trans->transid &&
+	    i_size_read(inode)) {
+		dcs = BTRFS_DC_SETUP;
+		goto out_put;
+	}
+
+	if (i_size_read(inode) > 0) {
+		ret = btrfs_check_trunc_cache_free_space(fs_info,
+					&fs_info->global_block_rsv);
+		if (ret)
+			goto out_put;
+
+		ret = btrfs_truncate_free_space_cache(trans, NULL, inode);
+		if (ret)
+			goto out_put;
+	}
+
+	spin_lock(&block_group->lock);
+	if (block_group->cached != BTRFS_CACHE_FINISHED ||
+	    !btrfs_test_opt(fs_info, SPACE_CACHE)) {
+		/*
+		 * don't bother trying to write stuff out _if_
+		 * a) we're not cached,
+		 * b) we're with nospace_cache mount option,
+		 * c) we're with v2 space_cache (FREE_SPACE_TREE).
+		 */
+		dcs = BTRFS_DC_WRITTEN;
+		spin_unlock(&block_group->lock);
+		goto out_put;
+	}
+	spin_unlock(&block_group->lock);
+
+	/*
+	 * We hit an ENOSPC when setting up the cache in this transaction, just
+	 * skip doing the setup, we've already cleared the cache so we're safe.
+	 */
+	if (test_bit(BTRFS_TRANS_CACHE_ENOSPC, &trans->transaction->flags)) {
+		ret = -ENOSPC;
+		goto out_put;
+	}
+
+	/*
+	 * Try to preallocate enough space based on how big the block group is.
+	 * Keep in mind this has to include any pinned space which could end up
+	 * taking up quite a bit since it's not folded into the other space
+	 * cache.
+	 */
+	cache_size = div_u64(block_group->length, SZ_256M);
+	if (!cache_size)
+		cache_size = 1;
+
+	cache_size *= 16;
+	cache_size *= fs_info->sectorsize;
+
+	ret = btrfs_check_data_free_space(BTRFS_I(inode), &data_reserved, 0,
+					  cache_size, false);
+	if (ret)
+		goto out_put;
+
+	ret = btrfs_prealloc_file_range_trans(inode, trans, 0, 0, cache_size,
+					      cache_size, cache_size,
+					      &alloc_hint);
+	/*
+	 * Our cache requires contiguous chunks so that we don't modify a bunch
+	 * of metadata or split extents when writing the cache out, which means
+	 * we can enospc if we are heavily fragmented in addition to just normal
+	 * out of space conditions.  So if we hit this just skip setting up any
+	 * other block groups for this transaction, maybe we'll unpin enough
+	 * space the next time around.
+	 */
+	if (!ret)
+		dcs = BTRFS_DC_SETUP;
+	else if (ret == -ENOSPC)
+		set_bit(BTRFS_TRANS_CACHE_ENOSPC, &trans->transaction->flags);
+
+out_put:
+	iput(inode);
+out_free:
+	btrfs_release_path(path);
+out:
+	spin_lock(&block_group->lock);
+	if (!ret && dcs == BTRFS_DC_SETUP)
+		block_group->cache_generation = trans->transid;
+	block_group->disk_cache_state = dcs;
+	spin_unlock(&block_group->lock);
+
+	extent_changeset_free(data_reserved);
+	return ret;
+}
+
+int btrfs_setup_space_cache(struct btrfs_trans_handle *trans)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_block_group *cache, *tmp;
+	struct btrfs_transaction *cur_trans = trans->transaction;
+	struct btrfs_path *path;
+
+	if (list_empty(&cur_trans->dirty_bgs) ||
+	    !btrfs_test_opt(fs_info, SPACE_CACHE))
+		return 0;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	/* Could add new block groups, use _safe just in case */
+	list_for_each_entry_safe(cache, tmp, &cur_trans->dirty_bgs,
+				 dirty_list) {
+		if (cache->disk_cache_state == BTRFS_DC_CLEAR)
+			cache_save_setup(cache, trans, path);
+	}
+
+	btrfs_free_path(path);
+	return 0;
+}
+
+/*
+ * Transaction commit does final block group cache writeback during a critical
+ * section where nothing is allowed to change the FS.  This is required in
+ * order for the cache to actually match the block group, but can introduce a
+ * lot of latency into the commit.
+ *
+ * So, btrfs_start_dirty_block_groups is here to kick off block group cache IO.
+ * There's a chance we'll have to redo some of it if the block group changes
+ * again during the commit, but it greatly reduces the commit latency by
+ * getting rid of the easy block groups while we're still allowing others to
+ * join the commit.
+ */
+int btrfs_start_dirty_block_groups(struct btrfs_trans_handle *trans)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_block_group *cache;
+	struct btrfs_transaction *cur_trans = trans->transaction;
+	int ret = 0;
+	int should_put;
+	struct btrfs_path *path = NULL;
+	LIST_HEAD(dirty);
+	struct list_head *io = &cur_trans->io_bgs;
+	int loops = 0;
+
+	spin_lock(&cur_trans->dirty_bgs_lock);
+	if (list_empty(&cur_trans->dirty_bgs)) {
+		spin_unlock(&cur_trans->dirty_bgs_lock);
+		return 0;
+	}
+	list_splice_init(&cur_trans->dirty_bgs, &dirty);
+	spin_unlock(&cur_trans->dirty_bgs_lock);
+
+again:
+	/* Make sure all the block groups on our dirty list actually exist */
+	btrfs_create_pending_block_groups(trans);
+
+	if (!path) {
+		path = btrfs_alloc_path();
+		if (!path) {
+			ret = -ENOMEM;
+			goto out;
+		}
+	}
+
+	/*
+	 * cache_write_mutex is here only to save us from balance or automatic
+	 * removal of empty block groups deleting this block group while we are
+	 * writing out the cache
+	 */
+	mutex_lock(&trans->transaction->cache_write_mutex);
+	while (!list_empty(&dirty)) {
+		bool drop_reserve = true;
+
+		cache = list_first_entry(&dirty, struct btrfs_block_group,
+					 dirty_list);
+		/*
+		 * This can happen if something re-dirties a block group that
+		 * is already under IO.  Just wait for it to finish and then do
+		 * it all again
+		 */
+		if (!list_empty(&cache->io_list)) {
+			list_del_init(&cache->io_list);
+			btrfs_wait_cache_io(trans, cache, path);
+			btrfs_put_block_group(cache);
+		}
+
+
+		/*
+		 * btrfs_wait_cache_io uses the cache->dirty_list to decide if
+		 * it should update the cache_state.  Don't delete until after
+		 * we wait.
+		 *
+		 * Since we're not running in the commit critical section
+		 * we need the dirty_bgs_lock to protect from update_block_group
+		 */
+		spin_lock(&cur_trans->dirty_bgs_lock);
+		list_del_init(&cache->dirty_list);
+		spin_unlock(&cur_trans->dirty_bgs_lock);
+
+		should_put = 1;
+
+		cache_save_setup(cache, trans, path);
+
+		if (cache->disk_cache_state == BTRFS_DC_SETUP) {
+			cache->io_ctl.inode = NULL;
+			ret = btrfs_write_out_cache(trans, cache, path);
+			if (ret == 0 && cache->io_ctl.inode) {
+				should_put = 0;
+
+				/*
+				 * The cache_write_mutex is protecting the
+				 * io_list, also refer to the definition of
+				 * btrfs_transaction::io_bgs for more details
+				 */
+				list_add_tail(&cache->io_list, io);
+			} else {
+				/*
+				 * If we failed to write the cache, the
+				 * generation will be bad and life goes on
+				 */
+				ret = 0;
+			}
+		}
+		if (!ret) {
+			ret = update_block_group_item(trans, path, cache);
+			/*
+			 * Our block group might still be attached to the list
+			 * of new block groups in the transaction handle of some
+			 * other task (struct btrfs_trans_handle->new_bgs). This
+			 * means its block group item isn't yet in the extent
+			 * tree. If this happens ignore the error, as we will
+			 * try again later in the critical section of the
+			 * transaction commit.
+			 */
+			if (ret == -ENOENT) {
+				ret = 0;
+				spin_lock(&cur_trans->dirty_bgs_lock);
+				if (list_empty(&cache->dirty_list)) {
+					list_add_tail(&cache->dirty_list,
+						      &cur_trans->dirty_bgs);
+					btrfs_get_block_group(cache);
+					drop_reserve = false;
+				}
+				spin_unlock(&cur_trans->dirty_bgs_lock);
+			} else if (ret) {
+				btrfs_abort_transaction(trans, ret);
+			}
+		}
+
+		/* If it's not on the io list, we need to put the block group */
+		if (should_put)
+			btrfs_put_block_group(cache);
+		if (drop_reserve)
+			btrfs_delayed_refs_rsv_release(fs_info, 1);
+		/*
+		 * Avoid blocking other tasks for too long. It might even save
+		 * us from writing caches for block groups that are going to be
+		 * removed.
+		 */
+		mutex_unlock(&trans->transaction->cache_write_mutex);
+		if (ret)
+			goto out;
+		mutex_lock(&trans->transaction->cache_write_mutex);
+	}
+	mutex_unlock(&trans->transaction->cache_write_mutex);
+
+	/*
+	 * Go through delayed refs for all the stuff we've just kicked off
+	 * and then loop back (just once)
+	 */
+	if (!ret)
+		ret = btrfs_run_delayed_refs(trans, 0);
+	if (!ret && loops == 0) {
+		loops++;
+		spin_lock(&cur_trans->dirty_bgs_lock);
+		list_splice_init(&cur_trans->dirty_bgs, &dirty);
+		/*
+		 * dirty_bgs_lock protects us from concurrent block group
+		 * deletes too (not just cache_write_mutex).
+		 */
+		if (!list_empty(&dirty)) {
+			spin_unlock(&cur_trans->dirty_bgs_lock);
+			goto again;
+		}
+		spin_unlock(&cur_trans->dirty_bgs_lock);
+	}
+out:
+	if (ret < 0) {
+		spin_lock(&cur_trans->dirty_bgs_lock);
+		list_splice_init(&dirty, &cur_trans->dirty_bgs);
+		spin_unlock(&cur_trans->dirty_bgs_lock);
+		btrfs_cleanup_dirty_bgs(cur_trans, fs_info);
+	}
+
+	btrfs_free_path(path);
+	return ret;
+}
+
+int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_block_group *cache;
+	struct btrfs_transaction *cur_trans = trans->transaction;
+	int ret = 0;
+	int should_put;
+	struct btrfs_path *path;
+	struct list_head *io = &cur_trans->io_bgs;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	/*
+	 * Even though we are in the critical section of the transaction commit,
+	 * we can still have concurrent tasks adding elements to this
+	 * transaction's list of dirty block groups. These tasks correspond to
+	 * endio free space workers started when writeback finishes for a
+	 * space cache, which run inode.c:btrfs_finish_ordered_io(), and can
+	 * allocate new block groups as a result of COWing nodes of the root
+	 * tree when updating the free space inode. The writeback for the space
+	 * caches is triggered by an earlier call to
+	 * btrfs_start_dirty_block_groups() and iterations of the following
+	 * loop.
+	 * Also we want to do the cache_save_setup first and then run the
+	 * delayed refs to make sure we have the best chance at doing this all
+	 * in one shot.
+	 */
+	spin_lock(&cur_trans->dirty_bgs_lock);
+	while (!list_empty(&cur_trans->dirty_bgs)) {
+		cache = list_first_entry(&cur_trans->dirty_bgs,
+					 struct btrfs_block_group,
+					 dirty_list);
+
+		/*
+		 * This can happen if cache_save_setup re-dirties a block group
+		 * that is already under IO.  Just wait for it to finish and
+		 * then do it all again
+		 */
+		if (!list_empty(&cache->io_list)) {
+			spin_unlock(&cur_trans->dirty_bgs_lock);
+			list_del_init(&cache->io_list);
+			btrfs_wait_cache_io(trans, cache, path);
+			btrfs_put_block_group(cache);
+			spin_lock(&cur_trans->dirty_bgs_lock);
+		}
+
+		/*
+		 * Don't remove from the dirty list until after we've waited on
+		 * any pending IO
+		 */
+		list_del_init(&cache->dirty_list);
+		spin_unlock(&cur_trans->dirty_bgs_lock);
+		should_put = 1;
+
+		cache_save_setup(cache, trans, path);
+
+		if (!ret)
+			ret = btrfs_run_delayed_refs(trans,
+						     (unsigned long) -1);
+
+		if (!ret && cache->disk_cache_state == BTRFS_DC_SETUP) {
+			cache->io_ctl.inode = NULL;
+			ret = btrfs_write_out_cache(trans, cache, path);
+			if (ret == 0 && cache->io_ctl.inode) {
+				should_put = 0;
+				list_add_tail(&cache->io_list, io);
+			} else {
+				/*
+				 * If we failed to write the cache, the
+				 * generation will be bad and life goes on
+				 */
+				ret = 0;
+			}
+		}
+		if (!ret) {
+			ret = update_block_group_item(trans, path, cache);
+			/*
+			 * One of the free space endio workers might have
+			 * created a new block group while updating a free space
+			 * cache's inode (at inode.c:btrfs_finish_ordered_io())
+			 * and hasn't released its transaction handle yet, in
+			 * which case the new block group is still attached to
+			 * its transaction handle and its creation has not
+			 * finished yet (no block group item in the extent tree
+			 * yet, etc). If this is the case, wait for all free
+			 * space endio workers to finish and retry. This is a
+			 * very rare case so no need for a more efficient and
+			 * complex approach.
+			 */
+			if (ret == -ENOENT) {
+				wait_event(cur_trans->writer_wait,
+				   atomic_read(&cur_trans->num_writers) == 1);
+				ret = update_block_group_item(trans, path, cache);
+			}
+			if (ret)
+				btrfs_abort_transaction(trans, ret);
+		}
+
+		/* If its not on the io list, we need to put the block group */
+		if (should_put)
+			btrfs_put_block_group(cache);
+		btrfs_delayed_refs_rsv_release(fs_info, 1);
+		spin_lock(&cur_trans->dirty_bgs_lock);
+	}
+	spin_unlock(&cur_trans->dirty_bgs_lock);
+
+	/*
+	 * Refer to the definition of io_bgs member for details why it's safe
+	 * to use it without any locking
+	 */
+	while (!list_empty(io)) {
+		cache = list_first_entry(io, struct btrfs_block_group,
+					 io_list);
+		list_del_init(&cache->io_list);
+		btrfs_wait_cache_io(trans, cache, path);
+		btrfs_put_block_group(cache);
+	}
+
+	btrfs_free_path(path);
+	return ret;
+}
+
+int btrfs_update_block_group(struct btrfs_trans_handle *trans,
+			     u64 bytenr, u64 num_bytes, bool alloc)
+{
+	struct btrfs_fs_info *info = trans->fs_info;
+	struct btrfs_block_group *cache = NULL;
+	u64 total = num_bytes;
+	u64 old_val;
+	u64 byte_in_group;
+	int factor;
+	int ret = 0;
+
+	/* Block accounting for super block */
+	spin_lock(&info->delalloc_root_lock);
+	old_val = btrfs_super_bytes_used(info->super_copy);
+	if (alloc)
+		old_val += num_bytes;
+	else
+		old_val -= num_bytes;
+	btrfs_set_super_bytes_used(info->super_copy, old_val);
+	spin_unlock(&info->delalloc_root_lock);
+
+	while (total) {
+		struct btrfs_space_info *space_info;
+		bool reclaim = false;
+
+		cache = btrfs_lookup_block_group(info, bytenr);
+		if (!cache) {
+			ret = -ENOENT;
+			break;
+		}
+		space_info = cache->space_info;
+		factor = btrfs_bg_type_to_factor(cache->flags);
+
+		/*
+		 * If this block group has free space cache written out, we
+		 * need to make sure to load it if we are removing space.  This
+		 * is because we need the unpinning stage to actually add the
+		 * space back to the block group, otherwise we will leak space.
+		 */
+		if (!alloc && !btrfs_block_group_done(cache))
+			btrfs_cache_block_group(cache, true);
+
+		byte_in_group = bytenr - cache->start;
+		WARN_ON(byte_in_group > cache->length);
+
+		spin_lock(&space_info->lock);
+		spin_lock(&cache->lock);
+
+		if (btrfs_test_opt(info, SPACE_CACHE) &&
+		    cache->disk_cache_state < BTRFS_DC_CLEAR)
+			cache->disk_cache_state = BTRFS_DC_CLEAR;
+
+		old_val = cache->used;
+		num_bytes = min(total, cache->length - byte_in_group);
+		if (alloc) {
+			old_val += num_bytes;
+			cache->used = old_val;
+			cache->reserved -= num_bytes;
+			space_info->bytes_reserved -= num_bytes;
+			space_info->bytes_used += num_bytes;
+			space_info->disk_used += num_bytes * factor;
+			spin_unlock(&cache->lock);
+			spin_unlock(&space_info->lock);
+		} else {
+			old_val -= num_bytes;
+			cache->used = old_val;
+			cache->pinned += num_bytes;
+			btrfs_space_info_update_bytes_pinned(info, space_info,
+							     num_bytes);
+			space_info->bytes_used -= num_bytes;
+			space_info->disk_used -= num_bytes * factor;
+
+			reclaim = should_reclaim_block_group(cache, num_bytes);
+
+			spin_unlock(&cache->lock);
+			spin_unlock(&space_info->lock);
+
+			set_extent_bit(&trans->transaction->pinned_extents,
+				       bytenr, bytenr + num_bytes - 1,
+				       EXTENT_DIRTY, NULL);
+		}
+
+		spin_lock(&trans->transaction->dirty_bgs_lock);
+		if (list_empty(&cache->dirty_list)) {
+			list_add_tail(&cache->dirty_list,
+				      &trans->transaction->dirty_bgs);
+			trans->delayed_ref_updates++;
+			btrfs_get_block_group(cache);
+		}
+		spin_unlock(&trans->transaction->dirty_bgs_lock);
+
+		/*
+		 * No longer have used bytes in this block group, queue it for
+		 * deletion. We do this after adding the block group to the
+		 * dirty list to avoid races between cleaner kthread and space
+		 * cache writeout.
+		 */
+		if (!alloc && old_val == 0) {
+			if (!btrfs_test_opt(info, DISCARD_ASYNC))
+				btrfs_mark_bg_unused(cache);
+		} else if (!alloc && reclaim) {
+			btrfs_mark_bg_to_reclaim(cache);
+		}
+
+		btrfs_put_block_group(cache);
+		total -= num_bytes;
+		bytenr += num_bytes;
+	}
+
+	/* Modified block groups are accounted for in the delayed_refs_rsv. */
+	btrfs_update_delayed_refs_rsv(trans);
+	return ret;
+}
+
+/*
+ * Update the block_group and space info counters.
+ *
+ * @cache:	The cache we are manipulating
+ * @ram_bytes:  The number of bytes of file content, and will be same to
+ *              @num_bytes except for the compress path.
+ * @num_bytes:	The number of bytes in question
+ * @delalloc:   The blocks are allocated for the delalloc write
+ *
+ * This is called by the allocator when it reserves space. If this is a
+ * reservation and the block group has become read only we cannot make the
+ * reservation and return -EAGAIN, otherwise this function always succeeds.
+ */
+int btrfs_add_reserved_bytes(struct btrfs_block_group *cache,
+			     u64 ram_bytes, u64 num_bytes, int delalloc,
+			     bool force_wrong_size_class)
+{
+	struct btrfs_space_info *space_info = cache->space_info;
+	enum btrfs_block_group_size_class size_class;
+	int ret = 0;
+
+	spin_lock(&space_info->lock);
+	spin_lock(&cache->lock);
+	if (cache->ro) {
+		ret = -EAGAIN;
+		goto out;
+	}
+
+	if (btrfs_block_group_should_use_size_class(cache)) {
+		size_class = btrfs_calc_block_group_size_class(num_bytes);
+		ret = btrfs_use_block_group_size_class(cache, size_class, force_wrong_size_class);
+		if (ret)
+			goto out;
+	}
+	cache->reserved += num_bytes;
+	space_info->bytes_reserved += num_bytes;
+	trace_btrfs_space_reservation(cache->fs_info, "space_info",
+				      space_info->flags, num_bytes, 1);
+	btrfs_space_info_update_bytes_may_use(cache->fs_info,
+					      space_info, -ram_bytes);
+	if (delalloc)
+		cache->delalloc_bytes += num_bytes;
+
+	/*
+	 * Compression can use less space than we reserved, so wake tickets if
+	 * that happens.
+	 */
+	if (num_bytes < ram_bytes)
+		btrfs_try_granting_tickets(cache->fs_info, space_info);
+out:
+	spin_unlock(&cache->lock);
+	spin_unlock(&space_info->lock);
+	return ret;
+}
+
+/*
+ * Update the block_group and space info counters.
+ *
+ * @cache:      The cache we are manipulating
+ * @num_bytes:  The number of bytes in question
+ * @delalloc:   The blocks are allocated for the delalloc write
+ *
+ * This is called by somebody who is freeing space that was never actually used
+ * on disk.  For example if you reserve some space for a new leaf in transaction
+ * A and before transaction A commits you free that leaf, you call this with
+ * reserve set to 0 in order to clear the reservation.
+ */
+void btrfs_free_reserved_bytes(struct btrfs_block_group *cache,
+			       u64 num_bytes, int delalloc)
+{
+	struct btrfs_space_info *space_info = cache->space_info;
+
+	spin_lock(&space_info->lock);
+	spin_lock(&cache->lock);
+	if (cache->ro)
+		space_info->bytes_readonly += num_bytes;
+	cache->reserved -= num_bytes;
+	space_info->bytes_reserved -= num_bytes;
+	space_info->max_extent_size = 0;
+
+	if (delalloc)
+		cache->delalloc_bytes -= num_bytes;
+	spin_unlock(&cache->lock);
+
+	btrfs_try_granting_tickets(cache->fs_info, space_info);
+	spin_unlock(&space_info->lock);
+}
+
+static void force_metadata_allocation(struct btrfs_fs_info *info)
+{
+	struct list_head *head = &info->space_info;
+	struct btrfs_space_info *found;
+
+	list_for_each_entry(found, head, list) {
+		if (found->flags & BTRFS_BLOCK_GROUP_METADATA)
+			found->force_alloc = CHUNK_ALLOC_FORCE;
+	}
+}
+
+static int should_alloc_chunk(struct btrfs_fs_info *fs_info,
+			      struct btrfs_space_info *sinfo, int force)
+{
+	u64 bytes_used = btrfs_space_info_used(sinfo, false);
+	u64 thresh;
+
+	if (force == CHUNK_ALLOC_FORCE)
+		return 1;
+
+	/*
+	 * in limited mode, we want to have some free space up to
+	 * about 1% of the FS size.
+	 */
+	if (force == CHUNK_ALLOC_LIMITED) {
+		thresh = btrfs_super_total_bytes(fs_info->super_copy);
+		thresh = max_t(u64, SZ_64M, mult_perc(thresh, 1));
+
+		if (sinfo->total_bytes - bytes_used < thresh)
+			return 1;
+	}
+
+	if (bytes_used + SZ_2M < mult_perc(sinfo->total_bytes, 80))
+		return 0;
+	return 1;
+}
+
+int btrfs_force_chunk_alloc(struct btrfs_trans_handle *trans, u64 type)
+{
+	u64 alloc_flags = btrfs_get_alloc_profile(trans->fs_info, type);
+
+	return btrfs_chunk_alloc(trans, alloc_flags, CHUNK_ALLOC_FORCE);
+}
+
+static struct btrfs_block_group *do_chunk_alloc(struct btrfs_trans_handle *trans, u64 flags)
+{
+	struct btrfs_block_group *bg;
+	int ret;
+
+	/*
+	 * Check if we have enough space in the system space info because we
+	 * will need to update device items in the chunk btree and insert a new
+	 * chunk item in the chunk btree as well. This will allocate a new
+	 * system block group if needed.
+	 */
+	check_system_chunk(trans, flags);
+
+	bg = btrfs_create_chunk(trans, flags);
+	if (IS_ERR(bg)) {
+		ret = PTR_ERR(bg);
+		goto out;
+	}
+
+	ret = btrfs_chunk_alloc_add_chunk_item(trans, bg);
+	/*
+	 * Normally we are not expected to fail with -ENOSPC here, since we have
+	 * previously reserved space in the system space_info and allocated one
+	 * new system chunk if necessary. However there are three exceptions:
+	 *
+	 * 1) We may have enough free space in the system space_info but all the
+	 *    existing system block groups have a profile which can not be used
+	 *    for extent allocation.
+	 *
+	 *    This happens when mounting in degraded mode. For example we have a
+	 *    RAID1 filesystem with 2 devices, lose one device and mount the fs
+	 *    using the other device in degraded mode. If we then allocate a chunk,
+	 *    we may have enough free space in the existing system space_info, but
+	 *    none of the block groups can be used for extent allocation since they
+	 *    have a RAID1 profile, and because we are in degraded mode with a
+	 *    single device, we are forced to allocate a new system chunk with a
+	 *    SINGLE profile. Making check_system_chunk() iterate over all system
+	 *    block groups and check if they have a usable profile and enough space
+	 *    can be slow on very large filesystems, so we tolerate the -ENOSPC and
+	 *    try again after forcing allocation of a new system chunk. Like this
+	 *    we avoid paying the cost of that search in normal circumstances, when
+	 *    we were not mounted in degraded mode;
+	 *
+	 * 2) We had enough free space info the system space_info, and one suitable
+	 *    block group to allocate from when we called check_system_chunk()
+	 *    above. However right after we called it, the only system block group
+	 *    with enough free space got turned into RO mode by a running scrub,
+	 *    and in this case we have to allocate a new one and retry. We only
+	 *    need do this allocate and retry once, since we have a transaction
+	 *    handle and scrub uses the commit root to search for block groups;
+	 *
+	 * 3) We had one system block group with enough free space when we called
+	 *    check_system_chunk(), but after that, right before we tried to
+	 *    allocate the last extent buffer we needed, a discard operation came
+	 *    in and it temporarily removed the last free space entry from the
+	 *    block group (discard removes a free space entry, discards it, and
+	 *    then adds back the entry to the block group cache).
+	 */
+	if (ret == -ENOSPC) {
+		const u64 sys_flags = btrfs_system_alloc_profile(trans->fs_info);
+		struct btrfs_block_group *sys_bg;
+
+		sys_bg = btrfs_create_chunk(trans, sys_flags);
+		if (IS_ERR(sys_bg)) {
+			ret = PTR_ERR(sys_bg);
+			btrfs_abort_transaction(trans, ret);
+			goto out;
+		}
+
+		ret = btrfs_chunk_alloc_add_chunk_item(trans, sys_bg);
+		if (ret) {
+			btrfs_abort_transaction(trans, ret);
+			goto out;
+		}
+
+		ret = btrfs_chunk_alloc_add_chunk_item(trans, bg);
+		if (ret) {
+			btrfs_abort_transaction(trans, ret);
+			goto out;
+		}
+	} else if (ret) {
+		btrfs_abort_transaction(trans, ret);
+		goto out;
+	}
+out:
+	btrfs_trans_release_chunk_metadata(trans);
+
+	if (ret)
+		return ERR_PTR(ret);
+
+	btrfs_get_block_group(bg);
+	return bg;
+}
+
+/*
+ * Chunk allocation is done in 2 phases:
+ *
+ * 1) Phase 1 - through btrfs_chunk_alloc() we allocate device extents for
+ *    the chunk, the chunk mapping, create its block group and add the items
+ *    that belong in the chunk btree to it - more specifically, we need to
+ *    update device items in the chunk btree and add a new chunk item to it.
+ *
+ * 2) Phase 2 - through btrfs_create_pending_block_groups(), we add the block
+ *    group item to the extent btree and the device extent items to the devices
+ *    btree.
+ *
+ * This is done to prevent deadlocks. For example when COWing a node from the
+ * extent btree we are holding a write lock on the node's parent and if we
+ * trigger chunk allocation and attempted to insert the new block group item
+ * in the extent btree right way, we could deadlock because the path for the
+ * insertion can include that parent node. At first glance it seems impossible
+ * to trigger chunk allocation after starting a transaction since tasks should
+ * reserve enough transaction units (metadata space), however while that is true
+ * most of the time, chunk allocation may still be triggered for several reasons:
+ *
+ * 1) When reserving metadata, we check if there is enough free space in the
+ *    metadata space_info and therefore don't trigger allocation of a new chunk.
+ *    However later when the task actually tries to COW an extent buffer from
+ *    the extent btree or from the device btree for example, it is forced to
+ *    allocate a new block group (chunk) because the only one that had enough
+ *    free space was just turned to RO mode by a running scrub for example (or
+ *    device replace, block group reclaim thread, etc), so we can not use it
+ *    for allocating an extent and end up being forced to allocate a new one;
+ *
+ * 2) Because we only check that the metadata space_info has enough free bytes,
+ *    we end up not allocating a new metadata chunk in that case. However if
+ *    the filesystem was mounted in degraded mode, none of the existing block
+ *    groups might be suitable for extent allocation due to their incompatible
+ *    profile (for e.g. mounting a 2 devices filesystem, where all block groups
+ *    use a RAID1 profile, in degraded mode using a single device). In this case
+ *    when the task attempts to COW some extent buffer of the extent btree for
+ *    example, it will trigger allocation of a new metadata block group with a
+ *    suitable profile (SINGLE profile in the example of the degraded mount of
+ *    the RAID1 filesystem);
+ *
+ * 3) The task has reserved enough transaction units / metadata space, but when
+ *    it attempts to COW an extent buffer from the extent or device btree for
+ *    example, it does not find any free extent in any metadata block group,
+ *    therefore forced to try to allocate a new metadata block group.
+ *    This is because some other task allocated all available extents in the
+ *    meanwhile - this typically happens with tasks that don't reserve space
+ *    properly, either intentionally or as a bug. One example where this is
+ *    done intentionally is fsync, as it does not reserve any transaction units
+ *    and ends up allocating a variable number of metadata extents for log
+ *    tree extent buffers;
+ *
+ * 4) The task has reserved enough transaction units / metadata space, but right
+ *    before it tries to allocate the last extent buffer it needs, a discard
+ *    operation comes in and, temporarily, removes the last free space entry from
+ *    the only metadata block group that had free space (discard starts by
+ *    removing a free space entry from a block group, then does the discard
+ *    operation and, once it's done, it adds back the free space entry to the
+ *    block group).
+ *
+ * We also need this 2 phases setup when adding a device to a filesystem with
+ * a seed device - we must create new metadata and system chunks without adding
+ * any of the block group items to the chunk, extent and device btrees. If we
+ * did not do it this way, we would get ENOSPC when attempting to update those
+ * btrees, since all the chunks from the seed device are read-only.
+ *
+ * Phase 1 does the updates and insertions to the chunk btree because if we had
+ * it done in phase 2 and have a thundering herd of tasks allocating chunks in
+ * parallel, we risk having too many system chunks allocated by many tasks if
+ * many tasks reach phase 1 without the previous ones completing phase 2. In the
+ * extreme case this leads to exhaustion of the system chunk array in the
+ * superblock. This is easier to trigger if using a btree node/leaf size of 64K
+ * and with RAID filesystems (so we have more device items in the chunk btree).
+ * This has happened before and commit eafa4fd0ad0607 ("btrfs: fix exhaustion of
+ * the system chunk array due to concurrent allocations") provides more details.
+ *
+ * Allocation of system chunks does not happen through this function. A task that
+ * needs to update the chunk btree (the only btree that uses system chunks), must
+ * preallocate chunk space by calling either check_system_chunk() or
+ * btrfs_reserve_chunk_metadata() - the former is used when allocating a data or
+ * metadata chunk or when removing a chunk, while the later is used before doing
+ * a modification to the chunk btree - use cases for the later are adding,
+ * removing and resizing a device as well as relocation of a system chunk.
+ * See the comment below for more details.
+ *
+ * The reservation of system space, done through check_system_chunk(), as well
+ * as all the updates and insertions into the chunk btree must be done while
+ * holding fs_info->chunk_mutex. This is important to guarantee that while COWing
+ * an extent buffer from the chunks btree we never trigger allocation of a new
+ * system chunk, which would result in a deadlock (trying to lock twice an
+ * extent buffer of the chunk btree, first time before triggering the chunk
+ * allocation and the second time during chunk allocation while attempting to
+ * update the chunks btree). The system chunk array is also updated while holding
+ * that mutex. The same logic applies to removing chunks - we must reserve system
+ * space, update the chunk btree and the system chunk array in the superblock
+ * while holding fs_info->chunk_mutex.
+ *
+ * This function, btrfs_chunk_alloc(), belongs to phase 1.
+ *
+ * If @force is CHUNK_ALLOC_FORCE:
+ *    - return 1 if it successfully allocates a chunk,
+ *    - return errors including -ENOSPC otherwise.
+ * If @force is NOT CHUNK_ALLOC_FORCE:
+ *    - return 0 if it doesn't need to allocate a new chunk,
+ *    - return 1 if it successfully allocates a chunk,
+ *    - return errors including -ENOSPC otherwise.
+ */
+int btrfs_chunk_alloc(struct btrfs_trans_handle *trans, u64 flags,
+		      enum btrfs_chunk_alloc_enum force)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_space_info *space_info;
+	struct btrfs_block_group *ret_bg;
+	bool wait_for_alloc = false;
+	bool should_alloc = false;
+	bool from_extent_allocation = false;
+	int ret = 0;
+
+	if (force == CHUNK_ALLOC_FORCE_FOR_EXTENT) {
+		from_extent_allocation = true;
+		force = CHUNK_ALLOC_FORCE;
+	}
+
+	/* Don't re-enter if we're already allocating a chunk */
+	if (trans->allocating_chunk)
+		return -ENOSPC;
+	/*
+	 * Allocation of system chunks can not happen through this path, as we
+	 * could end up in a deadlock if we are allocating a data or metadata
+	 * chunk and there is another task modifying the chunk btree.
+	 *
+	 * This is because while we are holding the chunk mutex, we will attempt
+	 * to add the new chunk item to the chunk btree or update an existing
+	 * device item in the chunk btree, while the other task that is modifying
+	 * the chunk btree is attempting to COW an extent buffer while holding a
+	 * lock on it and on its parent - if the COW operation triggers a system
+	 * chunk allocation, then we can deadlock because we are holding the
+	 * chunk mutex and we may need to access that extent buffer or its parent
+	 * in order to add the chunk item or update a device item.
+	 *
+	 * Tasks that want to modify the chunk tree should reserve system space
+	 * before updating the chunk btree, by calling either
+	 * btrfs_reserve_chunk_metadata() or check_system_chunk().
+	 * It's possible that after a task reserves the space, it still ends up
+	 * here - this happens in the cases described above at do_chunk_alloc().
+	 * The task will have to either retry or fail.
+	 */
+	if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
+		return -ENOSPC;
+
+	space_info = btrfs_find_space_info(fs_info, flags);
+	ASSERT(space_info);
+
+	do {
+		spin_lock(&space_info->lock);
+		if (force < space_info->force_alloc)
+			force = space_info->force_alloc;
+		should_alloc = should_alloc_chunk(fs_info, space_info, force);
+		if (space_info->full) {
+			/* No more free physical space */
+			if (should_alloc)
+				ret = -ENOSPC;
+			else
+				ret = 0;
+			spin_unlock(&space_info->lock);
+			return ret;
+		} else if (!should_alloc) {
+			spin_unlock(&space_info->lock);
+			return 0;
+		} else if (space_info->chunk_alloc) {
+			/*
+			 * Someone is already allocating, so we need to block
+			 * until this someone is finished and then loop to
+			 * recheck if we should continue with our allocation
+			 * attempt.
+			 */
+			wait_for_alloc = true;
+			force = CHUNK_ALLOC_NO_FORCE;
+			spin_unlock(&space_info->lock);
+			mutex_lock(&fs_info->chunk_mutex);
+			mutex_unlock(&fs_info->chunk_mutex);
+		} else {
+			/* Proceed with allocation */
+			space_info->chunk_alloc = 1;
+			wait_for_alloc = false;
+			spin_unlock(&space_info->lock);
+		}
+
+		cond_resched();
+	} while (wait_for_alloc);
+
+	mutex_lock(&fs_info->chunk_mutex);
+	trans->allocating_chunk = true;
+
+	/*
+	 * If we have mixed data/metadata chunks we want to make sure we keep
+	 * allocating mixed chunks instead of individual chunks.
+	 */
+	if (btrfs_mixed_space_info(space_info))
+		flags |= (BTRFS_BLOCK_GROUP_DATA | BTRFS_BLOCK_GROUP_METADATA);
+
+	/*
+	 * if we're doing a data chunk, go ahead and make sure that
+	 * we keep a reasonable number of metadata chunks allocated in the
+	 * FS as well.
+	 */
+	if (flags & BTRFS_BLOCK_GROUP_DATA && fs_info->metadata_ratio) {
+		fs_info->data_chunk_allocations++;
+		if (!(fs_info->data_chunk_allocations %
+		      fs_info->metadata_ratio))
+			force_metadata_allocation(fs_info);
+	}
+
+	ret_bg = do_chunk_alloc(trans, flags);
+	trans->allocating_chunk = false;
+
+	if (IS_ERR(ret_bg)) {
+		ret = PTR_ERR(ret_bg);
+	} else if (from_extent_allocation && (flags & BTRFS_BLOCK_GROUP_DATA)) {
+		/*
+		 * New block group is likely to be used soon. Try to activate
+		 * it now. Failure is OK for now.
+		 */
+		btrfs_zone_activate(ret_bg);
+	}
+
+	if (!ret)
+		btrfs_put_block_group(ret_bg);
+
+	spin_lock(&space_info->lock);
+	if (ret < 0) {
+		if (ret == -ENOSPC)
+			space_info->full = 1;
+		else
+			goto out;
+	} else {
+		ret = 1;
+		space_info->max_extent_size = 0;
+	}
+
+	space_info->force_alloc = CHUNK_ALLOC_NO_FORCE;
+out:
+	space_info->chunk_alloc = 0;
+	spin_unlock(&space_info->lock);
+	mutex_unlock(&fs_info->chunk_mutex);
+
+	return ret;
+}
+
+static u64 get_profile_num_devs(struct btrfs_fs_info *fs_info, u64 type)
+{
+	u64 num_dev;
+
+	num_dev = btrfs_raid_array[btrfs_bg_flags_to_raid_index(type)].devs_max;
+	if (!num_dev)
+		num_dev = fs_info->fs_devices->rw_devices;
+
+	return num_dev;
+}
+
+static void reserve_chunk_space(struct btrfs_trans_handle *trans,
+				u64 bytes,
+				u64 type)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_space_info *info;
+	u64 left;
+	int ret = 0;
+
+	/*
+	 * Needed because we can end up allocating a system chunk and for an
+	 * atomic and race free space reservation in the chunk block reserve.
+	 */
+	lockdep_assert_held(&fs_info->chunk_mutex);
+
+	info = btrfs_find_space_info(fs_info, BTRFS_BLOCK_GROUP_SYSTEM);
+	spin_lock(&info->lock);
+	left = info->total_bytes - btrfs_space_info_used(info, true);
+	spin_unlock(&info->lock);
+
+	if (left < bytes && btrfs_test_opt(fs_info, ENOSPC_DEBUG)) {
+		btrfs_info(fs_info, "left=%llu, need=%llu, flags=%llu",
+			   left, bytes, type);
+		btrfs_dump_space_info(fs_info, info, 0, 0);
+	}
+
+	if (left < bytes) {
+		u64 flags = btrfs_system_alloc_profile(fs_info);
+		struct btrfs_block_group *bg;
+
+		/*
+		 * Ignore failure to create system chunk. We might end up not
+		 * needing it, as we might not need to COW all nodes/leafs from
+		 * the paths we visit in the chunk tree (they were already COWed
+		 * or created in the current transaction for example).
+		 */
+		bg = btrfs_create_chunk(trans, flags);
+		if (IS_ERR(bg)) {
+			ret = PTR_ERR(bg);
+		} else {
+			/*
+			 * We have a new chunk. We also need to activate it for
+			 * zoned filesystem.
+			 */
+			ret = btrfs_zoned_activate_one_bg(fs_info, info, true);
+			if (ret < 0)
+				return;
+
+			/*
+			 * If we fail to add the chunk item here, we end up
+			 * trying again at phase 2 of chunk allocation, at
+			 * btrfs_create_pending_block_groups(). So ignore
+			 * any error here. An ENOSPC here could happen, due to
+			 * the cases described at do_chunk_alloc() - the system
+			 * block group we just created was just turned into RO
+			 * mode by a scrub for example, or a running discard
+			 * temporarily removed its free space entries, etc.
+			 */
+			btrfs_chunk_alloc_add_chunk_item(trans, bg);
+		}
+	}
+
+	if (!ret) {
+		ret = btrfs_block_rsv_add(fs_info,
+					  &fs_info->chunk_block_rsv,
+					  bytes, BTRFS_RESERVE_NO_FLUSH);
+		if (!ret)
+			trans->chunk_bytes_reserved += bytes;
+	}
+}
+
+/*
+ * Reserve space in the system space for allocating or removing a chunk.
+ * The caller must be holding fs_info->chunk_mutex.
+ */
+void check_system_chunk(struct btrfs_trans_handle *trans, u64 type)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	const u64 num_devs = get_profile_num_devs(fs_info, type);
+	u64 bytes;
+
+	/* num_devs device items to update and 1 chunk item to add or remove. */
+	bytes = btrfs_calc_metadata_size(fs_info, num_devs) +
+		btrfs_calc_insert_metadata_size(fs_info, 1);
+
+	reserve_chunk_space(trans, bytes, type);
+}
+
+/*
+ * Reserve space in the system space, if needed, for doing a modification to the
+ * chunk btree.
+ *
+ * @trans:		A transaction handle.
+ * @is_item_insertion:	Indicate if the modification is for inserting a new item
+ *			in the chunk btree or if it's for the deletion or update
+ *			of an existing item.
+ *
+ * This is used in a context where we need to update the chunk btree outside
+ * block group allocation and removal, to avoid a deadlock with a concurrent
+ * task that is allocating a metadata or data block group and therefore needs to
+ * update the chunk btree while holding the chunk mutex. After the update to the
+ * chunk btree is done, btrfs_trans_release_chunk_metadata() should be called.
+ *
+ */
+void btrfs_reserve_chunk_metadata(struct btrfs_trans_handle *trans,
+				  bool is_item_insertion)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	u64 bytes;
+
+	if (is_item_insertion)
+		bytes = btrfs_calc_insert_metadata_size(fs_info, 1);
+	else
+		bytes = btrfs_calc_metadata_size(fs_info, 1);
+
+	mutex_lock(&fs_info->chunk_mutex);
+	reserve_chunk_space(trans, bytes, BTRFS_BLOCK_GROUP_SYSTEM);
+	mutex_unlock(&fs_info->chunk_mutex);
+}
+
+void btrfs_put_block_group_cache(struct btrfs_fs_info *info)
+{
+	struct btrfs_block_group *block_group;
+
+	block_group = btrfs_lookup_first_block_group(info, 0);
+	while (block_group) {
+		btrfs_wait_block_group_cache_done(block_group);
+		spin_lock(&block_group->lock);
+		if (test_and_clear_bit(BLOCK_GROUP_FLAG_IREF,
+				       &block_group->runtime_flags)) {
+			struct inode *inode = block_group->inode;
+
+			block_group->inode = NULL;
+			spin_unlock(&block_group->lock);
+
+			ASSERT(block_group->io_ctl.inode == NULL);
+			iput(inode);
+		} else {
+			spin_unlock(&block_group->lock);
+		}
+		block_group = btrfs_next_block_group(block_group);
+	}
+}
+
+/*
+ * Must be called only after stopping all workers, since we could have block
+ * group caching kthreads running, and therefore they could race with us if we
+ * freed the block groups before stopping them.
+ */
+int btrfs_free_block_groups(struct btrfs_fs_info *info)
+{
+	struct btrfs_block_group *block_group;
+	struct btrfs_space_info *space_info;
+	struct btrfs_caching_control *caching_ctl;
+	struct rb_node *n;
+
+	if (btrfs_is_zoned(info)) {
+		if (info->active_meta_bg) {
+			btrfs_put_block_group(info->active_meta_bg);
+			info->active_meta_bg = NULL;
+		}
+		if (info->active_system_bg) {
+			btrfs_put_block_group(info->active_system_bg);
+			info->active_system_bg = NULL;
+		}
+	}
+
+	write_lock(&info->block_group_cache_lock);
+	while (!list_empty(&info->caching_block_groups)) {
+		caching_ctl = list_entry(info->caching_block_groups.next,
+					 struct btrfs_caching_control, list);
+		list_del(&caching_ctl->list);
+		btrfs_put_caching_control(caching_ctl);
+	}
+	write_unlock(&info->block_group_cache_lock);
+
+	spin_lock(&info->unused_bgs_lock);
+	while (!list_empty(&info->unused_bgs)) {
+		block_group = list_first_entry(&info->unused_bgs,
+					       struct btrfs_block_group,
+					       bg_list);
+		list_del_init(&block_group->bg_list);
+		btrfs_put_block_group(block_group);
+	}
+
+	while (!list_empty(&info->reclaim_bgs)) {
+		block_group = list_first_entry(&info->reclaim_bgs,
+					       struct btrfs_block_group,
+					       bg_list);
+		list_del_init(&block_group->bg_list);
+		btrfs_put_block_group(block_group);
+	}
+	spin_unlock(&info->unused_bgs_lock);
+
+	spin_lock(&info->zone_active_bgs_lock);
+	while (!list_empty(&info->zone_active_bgs)) {
+		block_group = list_first_entry(&info->zone_active_bgs,
+					       struct btrfs_block_group,
+					       active_bg_list);
+		list_del_init(&block_group->active_bg_list);
+		btrfs_put_block_group(block_group);
+	}
+	spin_unlock(&info->zone_active_bgs_lock);
+
+	write_lock(&info->block_group_cache_lock);
+	while ((n = rb_last(&info->block_group_cache_tree.rb_root)) != NULL) {
+		block_group = rb_entry(n, struct btrfs_block_group,
+				       cache_node);
+		rb_erase_cached(&block_group->cache_node,
+				&info->block_group_cache_tree);
+		RB_CLEAR_NODE(&block_group->cache_node);
+		write_unlock(&info->block_group_cache_lock);
+
+		down_write(&block_group->space_info->groups_sem);
+		list_del(&block_group->list);
+		up_write(&block_group->space_info->groups_sem);
+
+		/*
+		 * We haven't cached this block group, which means we could
+		 * possibly have excluded extents on this block group.
+		 */
+		if (block_group->cached == BTRFS_CACHE_NO ||
+		    block_group->cached == BTRFS_CACHE_ERROR)
+			btrfs_free_excluded_extents(block_group);
+
+		btrfs_remove_free_space_cache(block_group);
+		ASSERT(block_group->cached != BTRFS_CACHE_STARTED);
+		ASSERT(list_empty(&block_group->dirty_list));
+		ASSERT(list_empty(&block_group->io_list));
+		ASSERT(list_empty(&block_group->bg_list));
+		ASSERT(refcount_read(&block_group->refs) == 1);
+		ASSERT(block_group->swap_extents == 0);
+		btrfs_put_block_group(block_group);
+
+		write_lock(&info->block_group_cache_lock);
+	}
+	write_unlock(&info->block_group_cache_lock);
+
+	btrfs_release_global_block_rsv(info);
+
+	while (!list_empty(&info->space_info)) {
+		space_info = list_entry(info->space_info.next,
+					struct btrfs_space_info,
+					list);
+
+		/*
+		 * Do not hide this behind enospc_debug, this is actually
+		 * important and indicates a real bug if this happens.
+		 */
+		if (WARN_ON(space_info->bytes_pinned > 0 ||
+			    space_info->bytes_may_use > 0))
+			btrfs_dump_space_info(info, space_info, 0, 0);
+
+		/*
+		 * If there was a failure to cleanup a log tree, very likely due
+		 * to an IO failure on a writeback attempt of one or more of its
+		 * extent buffers, we could not do proper (and cheap) unaccounting
+		 * of their reserved space, so don't warn on bytes_reserved > 0 in
+		 * that case.
+		 */
+		if (!(space_info->flags & BTRFS_BLOCK_GROUP_METADATA) ||
+		    !BTRFS_FS_LOG_CLEANUP_ERROR(info)) {
+			if (WARN_ON(space_info->bytes_reserved > 0))
+				btrfs_dump_space_info(info, space_info, 0, 0);
+		}
+
+		WARN_ON(space_info->reclaim_size > 0);
+		list_del(&space_info->list);
+		btrfs_sysfs_remove_space_info(space_info);
+	}
+	return 0;
+}
+
+void btrfs_freeze_block_group(struct btrfs_block_group *cache)
+{
+	atomic_inc(&cache->frozen);
+}
+
+void btrfs_unfreeze_block_group(struct btrfs_block_group *block_group)
+{
+	struct btrfs_fs_info *fs_info = block_group->fs_info;
+	struct extent_map_tree *em_tree;
+	struct extent_map *em;
+	bool cleanup;
+
+	spin_lock(&block_group->lock);
+	cleanup = (atomic_dec_and_test(&block_group->frozen) &&
+		   test_bit(BLOCK_GROUP_FLAG_REMOVED, &block_group->runtime_flags));
+	spin_unlock(&block_group->lock);
+
+	if (cleanup) {
+		em_tree = &fs_info->mapping_tree;
+		write_lock(&em_tree->lock);
+		em = lookup_extent_mapping(em_tree, block_group->start,
+					   1);
+		BUG_ON(!em); /* logic error, can't happen */
+		remove_extent_mapping(em_tree, em);
+		write_unlock(&em_tree->lock);
+
+		/* once for us and once for the tree */
+		free_extent_map(em);
+		free_extent_map(em);
+
+		/*
+		 * We may have left one free space entry and other possible
+		 * tasks trimming this block group have left 1 entry each one.
+		 * Free them if any.
+		 */
+		btrfs_remove_free_space_cache(block_group);
+	}
+}
+
+bool btrfs_inc_block_group_swap_extents(struct btrfs_block_group *bg)
+{
+	bool ret = true;
+
+	spin_lock(&bg->lock);
+	if (bg->ro)
+		ret = false;
+	else
+		bg->swap_extents++;
+	spin_unlock(&bg->lock);
+
+	return ret;
+}
+
+void btrfs_dec_block_group_swap_extents(struct btrfs_block_group *bg, int amount)
+{
+	spin_lock(&bg->lock);
+	ASSERT(!bg->ro);
+	ASSERT(bg->swap_extents >= amount);
+	bg->swap_extents -= amount;
+	spin_unlock(&bg->lock);
+}
+
+enum btrfs_block_group_size_class btrfs_calc_block_group_size_class(u64 size)
+{
+	if (size <= SZ_128K)
+		return BTRFS_BG_SZ_SMALL;
+	if (size <= SZ_8M)
+		return BTRFS_BG_SZ_MEDIUM;
+	return BTRFS_BG_SZ_LARGE;
+}
+
+/*
+ * Handle a block group allocating an extent in a size class
+ *
+ * @bg:				The block group we allocated in.
+ * @size_class:			The size class of the allocation.
+ * @force_wrong_size_class:	Whether we are desperate enough to allow
+ *				mismatched size classes.
+ *
+ * Returns: 0 if the size class was valid for this block_group, -EAGAIN in the
+ * case of a race that leads to the wrong size class without
+ * force_wrong_size_class set.
+ *
+ * find_free_extent will skip block groups with a mismatched size class until
+ * it really needs to avoid ENOSPC. In that case it will set
+ * force_wrong_size_class. However, if a block group is newly allocated and
+ * doesn't yet have a size class, then it is possible for two allocations of
+ * different sizes to race and both try to use it. The loser is caught here and
+ * has to retry.
+ */
+int btrfs_use_block_group_size_class(struct btrfs_block_group *bg,
+				     enum btrfs_block_group_size_class size_class,
+				     bool force_wrong_size_class)
+{
+	ASSERT(size_class != BTRFS_BG_SZ_NONE);
+
+	/* The new allocation is in the right size class, do nothing */
+	if (bg->size_class == size_class)
+		return 0;
+	/*
+	 * The new allocation is in a mismatched size class.
+	 * This means one of two things:
+	 *
+	 * 1. Two tasks in find_free_extent for different size_classes raced
+	 *    and hit the same empty block_group. Make the loser try again.
+	 * 2. A call to find_free_extent got desperate enough to set
+	 *    'force_wrong_slab'. Don't change the size_class, but allow the
+	 *    allocation.
+	 */
+	if (bg->size_class != BTRFS_BG_SZ_NONE) {
+		if (force_wrong_size_class)
+			return 0;
+		return -EAGAIN;
+	}
+	/*
+	 * The happy new block group case: the new allocation is the first
+	 * one in the block_group so we set size_class.
+	 */
+	bg->size_class = size_class;
+
+	return 0;
+}
+
+bool btrfs_block_group_should_use_size_class(struct btrfs_block_group *bg)
+{
+	if (btrfs_is_zoned(bg->fs_info))
+		return false;
+	if (!btrfs_is_block_group_data_only(bg))
+		return false;
+	return true;
+}