btrfs: Convert fs_info->free_chunk_space to atomic64_t

The ->free_chunk_space variable is used to track the unallocated space
and access to it is protected by a spinlock, which is not used for
anything else.  Make the code a bit self-explanatory by switching the
variable to an atomic64_t type and kill the spinlock.
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
[ not a performance critical code, use of atomic type is ok ]
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -748,8 +748,7 @@ struct btrfs_fs_info {
 	struct rb_root block_group_cache_tree;
 
 	/* keep track of unallocated space */
-	spinlock_t free_chunk_lock;
-	u64 free_chunk_space;
+	atomic64_t free_chunk_space;
 
 	struct extent_io_tree freed_extents[2];
 	struct extent_io_tree *pinned_extents;

fs/btrfs/disk-io.c

@@ -2626,7 +2626,6 @@ int open_ctree(struct super_block *sb,
 	spin_lock_init(&fs_info->fs_roots_radix_lock);
 	spin_lock_init(&fs_info->delayed_iput_lock);
 	spin_lock_init(&fs_info->defrag_inodes_lock);
-	spin_lock_init(&fs_info->free_chunk_lock);
 	spin_lock_init(&fs_info->tree_mod_seq_lock);
 	spin_lock_init(&fs_info->super_lock);
 	spin_lock_init(&fs_info->qgroup_op_lock);
@@ -2667,7 +2666,7 @@ int open_ctree(struct super_block *sb,
 	fs_info->max_inline = BTRFS_DEFAULT_MAX_INLINE;
 	fs_info->metadata_ratio = 0;
 	fs_info->defrag_inodes = RB_ROOT;
-	fs_info->free_chunk_space = 0;
+	atomic64_set(&fs_info->free_chunk_space, 0);
 	fs_info->tree_mod_log = RB_ROOT;
 	fs_info->commit_interval = BTRFS_DEFAULT_COMMIT_INTERVAL;
 	fs_info->avg_delayed_ref_runtime = NSEC_PER_SEC >> 6; /* div by 64 */

fs/btrfs/extent-tree.c

@@ -4646,9 +4646,7 @@ static int can_overcommit(struct btrfs_root *root,
 
 	used += space_info->bytes_may_use;
 
-	spin_lock(&fs_info->free_chunk_lock);
-	avail = fs_info->free_chunk_space;
-	spin_unlock(&fs_info->free_chunk_lock);
+	avail = atomic64_read(&fs_info->free_chunk_space);
 
 	/*
 	 * If we have dup, raid1 or raid10 then only half of the free

fs/btrfs/volumes.c

@@ -2417,9 +2417,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
 	fs_info->fs_devices->total_devices++;
 	fs_info->fs_devices->total_rw_bytes += device->total_bytes;
 
-	spin_lock(&fs_info->free_chunk_lock);
-	fs_info->free_chunk_space += device->total_bytes;
-	spin_unlock(&fs_info->free_chunk_lock);
+	atomic64_add(device->total_bytes, &fs_info->free_chunk_space);
 
 	if (!blk_queue_nonrot(q))
 		fs_info->fs_devices->rotating = 1;
@@ -2874,9 +2872,7 @@ int btrfs_remove_chunk(struct btrfs_trans_handle *trans,
 			mutex_lock(&fs_info->chunk_mutex);
 			btrfs_device_set_bytes_used(device,
 					device->bytes_used - dev_extent_len);
-			spin_lock(&fs_info->free_chunk_lock);
-			fs_info->free_chunk_space += dev_extent_len;
-			spin_unlock(&fs_info->free_chunk_lock);
+			atomic64_add(dev_extent_len, &fs_info->free_chunk_space);
 			btrfs_clear_space_info_full(fs_info);
 			mutex_unlock(&fs_info->chunk_mutex);
 		}
@@ -4409,9 +4405,7 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
 	btrfs_device_set_total_bytes(device, new_size);
 	if (device->writeable) {
 		device->fs_devices->total_rw_bytes -= diff;
-		spin_lock(&fs_info->free_chunk_lock);
-		fs_info->free_chunk_space -= diff;
-		spin_unlock(&fs_info->free_chunk_lock);
+		atomic64_sub(diff, &fs_info->free_chunk_space);
 	}
 	mutex_unlock(&fs_info->chunk_mutex);
 
@@ -4535,9 +4529,7 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
 		btrfs_device_set_total_bytes(device, old_size);
 		if (device->writeable)
 			device->fs_devices->total_rw_bytes += diff;
-		spin_lock(&fs_info->free_chunk_lock);
-		fs_info->free_chunk_space += diff;
-		spin_unlock(&fs_info->free_chunk_lock);
+		atomic64_add(diff, &fs_info->free_chunk_space);
 		mutex_unlock(&fs_info->chunk_mutex);
 	}
 	return ret;
@@ -4882,9 +4874,7 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
 		btrfs_device_set_bytes_used(map->stripes[i].dev, num_bytes);
 	}
 
-	spin_lock(&info->free_chunk_lock);
-	info->free_chunk_space -= (stripe_size * map->num_stripes);
-	spin_unlock(&info->free_chunk_lock);
+	atomic64_sub(stripe_size * map->num_stripes, &info->free_chunk_space);
 
 	free_extent_map(em);
 	check_raid56_incompat_flag(info, type);
@@ -6684,10 +6674,8 @@ static int read_one_dev(struct btrfs_fs_info *fs_info,
 	device->in_fs_metadata = 1;
 	if (device->writeable && !device->is_tgtdev_for_dev_replace) {
 		device->fs_devices->total_rw_bytes += device->total_bytes;
-		spin_lock(&fs_info->free_chunk_lock);
-		fs_info->free_chunk_space += device->total_bytes -
-			device->bytes_used;
-		spin_unlock(&fs_info->free_chunk_lock);
+		atomic64_add(device->total_bytes - device->bytes_used,
+				&fs_info->free_chunk_space);
 	}
 	ret = 0;
 	return ret;