void ext4_release_system_zone(struct super_block *sb)
{
	struct ext4_system_blocks *system_blks;

	system_blks = rcu_dereference_protected(EXT4_SB(sb)->system_blks,
					lockdep_is_held(&sb->s_umount));
	rcu_assign_pointer(EXT4_SB(sb)->system_blks, NULL);

	if (system_blks)
		call_rcu(&system_blks->rcu, ext4_destroy_system_zone);
}
void ext4_release_system_zone(struct super_block *sb)
{
	struct ext4_system_blocks *system_blks;

	system_blks = rcu_dereference_protected(EXT4_SB(sb)->system_blks,
					lockdep_is_held(&sb->s_umount));
	rcu_assign_pointer(EXT4_SB(sb)->system_blks, NULL);

	if (system_blks)
		call_rcu(&system_blks->rcu, ext4_destroy_system_zone);
}