iomap: avoid avoid truncating 64-bit offset to 32 bits

commit c13094b894de289514d84b8db56d1f2931a0bade upstream.

on 32-bit kernels, iomap_write_delalloc_scan() was inadvertently using a
32-bit position due to folio_next_index() returning an unsigned long.
This could lead to an infinite loop when writing to an xfs filesystem.

Signed-off-by: Marco Nelissen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Darrick J. Wong <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

fs/iomap/buffered-io.c

@@ -1138,7 +1138,7 @@ static void iomap_write_delalloc_scan(struct inode *inode,
 				start_byte, end_byte, iomap, punch);
 
 		/* move offset to start of next folio in range */
-		start_byte = folio_next_index(folio) << PAGE_SHIFT;
+		start_byte = folio_pos(folio) + folio_size(folio);
 		folio_unlock(folio);
 		folio_put(folio);
 	}