exfat: fix erroneous discard when clear cluster bit

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: NHyeongseok Kim <hyeongseok@gmail.com>
Acked-by: NSungjong Seo <sj1557.seo@samsung.com>
Signed-off-by: NNamjae Jeon <namjae.jeon@samsung.com>

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, bool sync)
 {
 	int i, b;
@@ -186,8 +178,7 @@ void exfat_clear_bitmap(struct inode *inode, unsigned int clu, bool sync)
 		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) {