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

commit c13094b 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 <marco.nelissen@gmail.com>
Link: https://lore.kernel.org/r/20250109041253.2494374-1-marco.nelissen@gmail.com
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: marcone

fs/iomap/buffered-io.c

@@ -1095,7 +1095,7 @@ static int iomap_write_delalloc_scan(struct inode *inode,
 		}
 
 		/* 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);
 	}