f2fs: fix race condition in between free nid allocator/initializer

In below concurrent case, allocated nid can be loaded into free nid cache
and be allocated again.

Thread A				Thread B
- f2fs_create
 - f2fs_new_inode
  - alloc_nid
   - __insert_nid_to_list(ALLOC_NID_LIST)
					- f2fs_balance_fs_bg
					 - build_free_nids
					  - __build_free_nids
					   - scan_nat_page
					    - add_free_nid
					     - __lookup_nat_cache
 - f2fs_add_link
  - init_inode_metadata
   - new_inode_page
    - new_node_page
     - set_node_addr
 - alloc_nid_done
  - __remove_nid_from_list(ALLOC_NID_LIST)
					     - __insert_nid_to_list(FREE_NID_LIST)

This patch makes nat cache lookup and free nid list operation being atomical
to avoid this race condition.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
static int init_node_manager(struct f2fs_sb_info *sbi)
{
	struct f2fs_super_block *sb_raw = F2FS_RAW_SUPER(sbi);
	struct f2fs_nm_info *nm_i = NM_I(sbi);
	unsigned char *version_bitmap;
	unsigned int nat_segs;
	int err;

	nm_i->nat_blkaddr = le32_to_cpu(sb_raw->nat_blkaddr);

	/* segment_count_nat includes pair segment so divide to 2. */
	nat_segs = le32_to_cpu(sb_raw->segment_count_nat) >> 1;
	nm_i->nat_blocks = nat_segs << le32_to_cpu(sb_raw->log_blocks_per_seg);
	nm_i->max_nid = NAT_ENTRY_PER_BLOCK * nm_i->nat_blocks;

	/* not used nids: 0, node, meta, (and root counted as valid node) */
	nm_i->available_nids = nm_i->max_nid - sbi->total_valid_node_count -
							F2FS_RESERVED_NODE_NUM;
	nm_i->nid_cnt[FREE_NID_LIST] = 0;
	nm_i->nid_cnt[ALLOC_NID_LIST] = 0;
	nm_i->nat_cnt = 0;
	nm_i->ram_thresh = DEF_RAM_THRESHOLD;
	nm_i->ra_nid_pages = DEF_RA_NID_PAGES;
	nm_i->dirty_nats_ratio = DEF_DIRTY_NAT_RATIO_THRESHOLD;

	INIT_RADIX_TREE(&nm_i->free_nid_root, GFP_ATOMIC);
	INIT_LIST_HEAD(&nm_i->nid_list[FREE_NID_LIST]);
	INIT_LIST_HEAD(&nm_i->nid_list[ALLOC_NID_LIST]);
	INIT_RADIX_TREE(&nm_i->nat_root, GFP_NOIO);
	INIT_RADIX_TREE(&nm_i->nat_set_root, GFP_NOIO);
	INIT_LIST_HEAD(&nm_i->nat_entries);

	mutex_init(&nm_i->build_lock);
	spin_lock_init(&nm_i->nid_list_lock);
	init_rwsem(&nm_i->nat_tree_lock);

	nm_i->next_scan_nid = le32_to_cpu(sbi->ckpt->next_free_nid);
	nm_i->bitmap_size = __bitmap_size(sbi, NAT_BITMAP);
	version_bitmap = __bitmap_ptr(sbi, NAT_BITMAP);
	if (!version_bitmap)
		return -EFAULT;

	nm_i->nat_bitmap = kmemdup(version_bitmap, nm_i->bitmap_size,
					GFP_KERNEL);
	if (!nm_i->nat_bitmap)
		return -ENOMEM;

	err = __get_nat_bitmaps(sbi);
	if (err)
		return err;

#ifdef CONFIG_F2FS_CHECK_FS
	nm_i->nat_bitmap_mir = kmemdup(version_bitmap, nm_i->bitmap_size,
					GFP_KERNEL);
	if (!nm_i->nat_bitmap_mir)
		return -ENOMEM;
#endif

	return 0;
}

static int init_node_manager(struct f2fs_sb_info *sbi)
{
	struct f2fs_super_block *sb_raw = F2FS_RAW_SUPER(sbi);
	struct f2fs_nm_info *nm_i = NM_I(sbi);
	unsigned char *version_bitmap;
	unsigned int nat_segs;
	int err;

	nm_i->nat_blkaddr = le32_to_cpu(sb_raw->nat_blkaddr);

	/* segment_count_nat includes pair segment so divide to 2. */
	nat_segs = le32_to_cpu(sb_raw->segment_count_nat) >> 1;
	nm_i->nat_blocks = nat_segs << le32_to_cpu(sb_raw->log_blocks_per_seg);
	nm_i->max_nid = NAT_ENTRY_PER_BLOCK * nm_i->nat_blocks;

	/* not used nids: 0, node, meta, (and root counted as valid node) */
	nm_i->available_nids = nm_i->max_nid - sbi->total_valid_node_count -
							F2FS_RESERVED_NODE_NUM;
	nm_i->nid_cnt[FREE_NID_LIST] = 0;
	nm_i->nid_cnt[ALLOC_NID_LIST] = 0;
	nm_i->nat_cnt = 0;
	nm_i->ram_thresh = DEF_RAM_THRESHOLD;
	nm_i->ra_nid_pages = DEF_RA_NID_PAGES;
	nm_i->dirty_nats_ratio = DEF_DIRTY_NAT_RATIO_THRESHOLD;

	INIT_RADIX_TREE(&nm_i->free_nid_root, GFP_ATOMIC);
	INIT_LIST_HEAD(&nm_i->nid_list[FREE_NID_LIST]);
	INIT_LIST_HEAD(&nm_i->nid_list[ALLOC_NID_LIST]);
	INIT_RADIX_TREE(&nm_i->nat_root, GFP_NOIO);
	INIT_RADIX_TREE(&nm_i->nat_set_root, GFP_NOIO);
	INIT_LIST_HEAD(&nm_i->nat_entries);

	mutex_init(&nm_i->build_lock);
	spin_lock_init(&nm_i->nid_list_lock);
	init_rwsem(&nm_i->nat_tree_lock);

	nm_i->next_scan_nid = le32_to_cpu(sbi->ckpt->next_free_nid);
	nm_i->bitmap_size = __bitmap_size(sbi, NAT_BITMAP);
	version_bitmap = __bitmap_ptr(sbi, NAT_BITMAP);
	if (!version_bitmap)
		return -EFAULT;

	nm_i->nat_bitmap = kmemdup(version_bitmap, nm_i->bitmap_size,
					GFP_KERNEL);
	if (!nm_i->nat_bitmap)
		return -ENOMEM;

	err = __get_nat_bitmaps(sbi);
	if (err)
		return err;

#ifdef CONFIG_F2FS_CHECK_FS
	nm_i->nat_bitmap_mir = kmemdup(version_bitmap, nm_i->bitmap_size,
					GFP_KERNEL);
	if (!nm_i->nat_bitmap_mir)
		return -ENOMEM;
#endif

	return 0;
}
