ext4: fix xattr block allocation/release with bigalloc

Currently when new xattr block is created or released we we would call
dquot_free_block() or dquot_alloc_block() respectively, among the else
decrementing or incrementing the number of blocks assigned to the
inode by one block.

This however does not work for bigalloc file system because we always
allocate/free the whole cluster so we have to count with that in
dquot_free_block() and dquot_alloc_block() as well.

Use the clusters-to-blocks conversion EXT4_C2B() when passing number of
blocks to the dquot_alloc/free functions to fix the problem.

The problem has been revealed by xfstests #117 (and possibly others).

Signed-off-by: Lukas Czerner <[e-mail]>
Signed-off-by: "Theodore Ts'o" <[e-mail]>
Reviewed-by: Eric Sandeen <[e-mail]>
Cc: [e-mail]

fs/ext4/xattr.c

···
 		error = ext4_handle_dirty_xattr_block(handle, inode, bh);
 		if (IS_SYNC(inode))
 			ext4_handle_sync(handle);
-		dquot_free_block(inode, 1);
+		dquot_free_block(inode, EXT4_C2B(EXT4_SB(inode->i_sb), 1));
 		ea_bdebug(bh, "refcount now=%d; releasing",
 			  le32_to_cpu(BHDR(bh)->h_refcount));
 	}
···
 			else {
 				/* The old block is released after updating
 				   the inode. */
-				error = dquot_alloc_block(inode, 1);
+				error = dquot_alloc_block(inode,
+						EXT4_C2B(EXT4_SB(sb), 1));
 				if (error)
 					goto cleanup;
 				error = ext4_journal_get_write_access(handle,
···
 	return error;
 
 cleanup_dquot:
-	dquot_free_block(inode, 1);
+	dquot_free_block(inode, EXT4_C2B(EXT4_SB(sb), 1));
 	goto cleanup;
 
 bad_block: