f2fs: fix to avoid potential race on sbi->unusable_block_count access/update

Use sbi.stat_lock to protect sbi->unusable_block_count accesss/udpate, in
order to avoid potential race on it.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/checkpoint.c

@@ -1536,7 +1536,11 @@ static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 	clear_sbi_flag(sbi, SBI_IS_DIRTY);
 	clear_sbi_flag(sbi, SBI_NEED_CP);
 	clear_sbi_flag(sbi, SBI_QUOTA_SKIP_FLUSH);
+
+	spin_lock(&sbi->stat_lock);
 	sbi->unusable_block_count = 0;
+	spin_unlock(&sbi->stat_lock);
+
 	__set_cp_next_pack(sbi);
 
 	/*

fs/f2fs/segment.c

@@ -2169,8 +2169,11 @@ static void update_sit_entry(struct f2fs_sb_info *sbi, block_t blkaddr, int del)
 			 * before, we must track that to know how much space we
 			 * really have.
 			 */
-			if (f2fs_test_bit(offset, se->ckpt_valid_map))
+			if (f2fs_test_bit(offset, se->ckpt_valid_map)) {
+				spin_lock(&sbi->stat_lock);
 				sbi->unusable_block_count++;
+				spin_unlock(&sbi->stat_lock);
+			}
 		}
 
 		if (f2fs_test_and_clear_bit(offset, se->discard_map))

fs/f2fs/super.c

@@ -1226,10 +1226,13 @@ static int f2fs_statfs(struct dentry *dentry, struct kstatfs *buf)
 	buf->f_blocks = total_count - start_count;
 	buf->f_bfree = user_block_count - valid_user_blocks(sbi) -
 						sbi->current_reserved_blocks;
+
+	spin_lock(&sbi->stat_lock);
 	if (unlikely(buf->f_bfree <= sbi->unusable_block_count))
 		buf->f_bfree = 0;
 	else
 		buf->f_bfree -= sbi->unusable_block_count;
+	spin_unlock(&sbi->stat_lock);
 
 	if (buf->f_bfree > F2FS_OPTION(sbi).root_reserved_blocks)
 		buf->f_bavail = buf->f_bfree -
@@ -1508,7 +1511,10 @@ static int f2fs_disable_checkpoint(struct f2fs_sb_info *sbi)
 	if (err)
 		goto out_unlock;
 
+	spin_lock(&sbi->stat_lock);
 	sbi->unusable_block_count = 0;
+	spin_unlock(&sbi->stat_lock);
+
 out_unlock:
 	mutex_unlock(&sbi->gc_mutex);
 restore_flag: