ext4: Convert s_blocks_count to s_blocks_count_lo

Convert s_blocks_count to s_blocks_count_lo
This helps in finding BUGs due to direct partial access of
these split 64 bit values

Also fix direct partial access in ext4 code
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

fs/ext4/super.c

@@ -2667,7 +2667,7 @@ static int ext4_statfs (struct dentry * dentry, struct kstatfs * buf)
 
 	if (test_opt(sb, MINIX_DF)) {
 		sbi->s_overhead_last = 0;
-	} else if (sbi->s_blocks_last != le32_to_cpu(es->s_blocks_count)) {
+	} else if (sbi->s_blocks_last != ext4_blocks_count(es)) {
 		unsigned long ngroups = sbi->s_groups_count, i;
 		ext4_fsblk_t overhead = 0;
 		smp_rmb();
@@ -2702,7 +2702,7 @@ static int ext4_statfs (struct dentry * dentry, struct kstatfs * buf)
 		overhead += ngroups * (2 + sbi->s_itb_per_group);
 		sbi->s_overhead_last = overhead;
 		smp_wmb();
-		sbi->s_blocks_last = le32_to_cpu(es->s_blocks_count);
+		sbi->s_blocks_last = ext4_blocks_count(es);
 	}
 
 	buf->f_type = EXT4_SUPER_MAGIC;

include/linux/ext4_fs.h

@@ -501,7 +501,7 @@ do {									       \
  */
 struct ext4_super_block {
 /*00*/	__le32	s_inodes_count;		/* Inodes count */
-	__le32	s_blocks_count;		/* Blocks count */
+	__le32	s_blocks_count_lo;	/* Blocks count */
 	__le32	s_r_blocks_count;	/* Reserved blocks count */
 	__le32	s_free_blocks_count;	/* Free blocks count */
 /*10*/	__le32	s_free_inodes_count;	/* Free inodes count */
@@ -981,7 +981,7 @@ extern void ext4_inode_table_set(struct super_block *sb,
 static inline ext4_fsblk_t ext4_blocks_count(struct ext4_super_block *es)
 {
 	return ((ext4_fsblk_t)le32_to_cpu(es->s_blocks_count_hi) << 32) |
-		le32_to_cpu(es->s_blocks_count);
+		le32_to_cpu(es->s_blocks_count_lo);
 }
 
 static inline ext4_fsblk_t ext4_r_blocks_count(struct ext4_super_block *es)
@@ -999,7 +999,7 @@ static inline ext4_fsblk_t ext4_free_blocks_count(struct ext4_super_block *es)
 static inline void ext4_blocks_count_set(struct ext4_super_block *es,
 					 ext4_fsblk_t blk)
 {
-	es->s_blocks_count = cpu_to_le32((u32)blk);
+	es->s_blocks_count_lo = cpu_to_le32((u32)blk);
 	es->s_blocks_count_hi = cpu_to_le32(blk >> 32);
 }