+ /*
+ * We acquire fs_info->chunk_mutex for 2 reasons:
+ *
+ * 1) Just like with the first phase of the chunk allocation, we must
+ * reserve system space, do all chunk btree updates and deletions, and
+ * update the system chunk array in the superblock while holding this
+ * mutex. This is for similar reasons as explained on the comment at
+ * the top of btrfs_chunk_alloc();
+ *
+ * 2) 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, which would cause a failure when updating
+ * the device item, which does not exists on the chunk btree.
+ * The finishing phase of device replace acquires both the
+ * device_list_mutex and the chunk_mutex, in that order, so we are
+ * safe by just acquiring the chunk_mutex.
+ */
+ trans->removing_chunk = true;
+ mutex_lock(&fs_info->chunk_mutex);
+
+ check_system_chunk(trans, map->type);
+
+ ret = remove_chunk_item(trans, map, chunk_offset);
+ /*
+ * Normally we should not get -ENOSPC since we reserved space before
+ * through the call to check_system_chunk().
+ *
+ * Despite our system space_info having enough free space, we may not
+ * be able to allocate extents from its block groups, because all have
+ * an incompatible profile, which will force us to allocate a new system
+ * block group with the right profile, or right after we called
+ * check_system_space() above, a scrub turned the only system block group
+ * with enough free space into RO mode.
+ * This is explained with more detail at do_chunk_alloc().
+ *
+ * So if we get -ENOSPC, allocate a new system chunk and retry once.
+ */
+ if (ret == -ENOSPC) {
+ const u64 sys_flags = btrfs_system_alloc_profile(fs_info);
+ struct btrfs_block_group *sys_bg;
+
+ sys_bg = btrfs_alloc_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);