exfat: fix erroneous discard when clear cluster bit

commit 77edfc6e upstream.

If mounted with discard option, exFAT issues discard command when clear
cluster bit to remove file. But the input parameter of cluster-to-sector
calculation is abnormally added by reserved cluster size which is 2,
leading to discard unrelated sectors included in target+2 cluster.
With fixing this, remove the wrong comments in set/clear/find bitmap
functions.

Fixes: 1e49a94c ("exfat: add bitmap operations")
Cc: stable@vger.kernel.org # v5.7+
Signed-off-by: Hyeongseok Kim <hyeongseok@gmail.com>
Acked-by: Sungjong Seo <sj1557.seo@samsung.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/exfat/balloc.c

@@ -141,10 +141,6 @@ void exfat_free_bitmap(struct exfat_sb_info *sbi)
 	kfree(sbi->vol_amap);
 }
 
-/*
- * If the value of "clu" is 0, it means cluster 2 which is the first cluster of
- * the cluster heap.
- */
 int exfat_set_bitmap(struct inode *inode, unsigned int clu)
 {
 	int i, b;
@@ -162,10 +158,6 @@ int exfat_set_bitmap(struct inode *inode, unsigned int clu)
 	return 0;
 }
 
-/*
- * If the value of "clu" is 0, it means cluster 2 which is the first cluster of
- * the cluster heap.
- */
 void exfat_clear_bitmap(struct inode *inode, unsigned int clu)
 {
 	int i, b;
@@ -186,8 +178,7 @@ void exfat_clear_bitmap(struct inode *inode, unsigned int clu)
 		int ret_discard;
 
 		ret_discard = sb_issue_discard(sb,
-			exfat_cluster_to_sector(sbi, clu +
-						EXFAT_RESERVED_CLUSTERS),
+			exfat_cluster_to_sector(sbi, clu),
 			(1 << sbi->sect_per_clus_bits), GFP_NOFS, 0);
 
 		if (ret_discard == -EOPNOTSUPP) {