fat: Fix fat_ent_update_ptr() for FAT12

This fixes the missing update for bhs/nr_bhs in case the caller
accessed from block boundary to first block of boundary.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/fat/fatent.c

@@ -317,10 +317,20 @@ static inline int fat_ent_update_ptr(struct super_block *sb,
 	/* Is this fatent's blocks including this entry? */
 	if (!fatent->nr_bhs || bhs[0]->b_blocknr != blocknr)
 		return 0;
-	/* Does this entry need the next block? */
-	if (sbi->fat_bits == 12 && (offset + 1) >= sb->s_blocksize) {
-		if (fatent->nr_bhs != 2 || bhs[1]->b_blocknr != (blocknr + 1))
-			return 0;
+	if (sbi->fat_bits == 12) {
+		if ((offset + 1) < sb->s_blocksize) {
+			/* This entry is on bhs[0]. */
+			if (fatent->nr_bhs == 2) {
+				brelse(bhs[1]);
+				fatent->nr_bhs = 1;
+			}
+		} else {
+			/* This entry needs the next block. */
+			if (fatent->nr_bhs != 2)
+				return 0;
+			if (bhs[1]->b_blocknr != (blocknr + 1))
+				return 0;
+		}
 	}
 	ops->ent_set_ptr(fatent, offset);
 	return 1;