f2fs: limit b_size of mapped bh in f2fs_map_bh

Map bh over max size which caller defined is not needed, limit it in
f2fs_map_bh.
Signed-off-by: NChao Yu <chao2.yu@samsung.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -255,15 +255,13 @@ static void f2fs_map_bh(struct super_block *sb, pgoff_t pgofs,
 			struct extent_info *ei, struct buffer_head *bh_result)
 {
 	unsigned int blkbits = sb->s_blocksize_bits;
-	size_t count;
+	size_t max_size = bh_result->b_size;
+	size_t mapped_size;
 
 	clear_buffer_new(bh_result);
 	map_bh(bh_result, sb, ei->blk + pgofs - ei->fofs);
-	count = ei->fofs + ei->len - pgofs;
-	if (count < (UINT_MAX >> blkbits))
-		bh_result->b_size = (count << blkbits);
-	else
-		bh_result->b_size = UINT_MAX;
+	mapped_size = (ei->fofs + ei->len - pgofs) << blkbits;
+	bh_result->b_size = min(max_size, mapped_size);
 }
 
 static bool lookup_extent_info(struct inode *inode, pgoff_t pgofs,