fs: Extra data cache flush (workaround)

Taken from linux-2.6.31.3-jz-20110809-FR1.patch.gz.

TODO: Investigate whether the problem this patch works around is due to
      flush_kernel_dcache_page() being unimplemented on MIPS.

fs/mpage.c

@@ -54,6 +54,17 @@ static void mpage_end_io(struct bio *bio, int err)
 		if (bio_data_dir(bio) == READ) {
 			if (uptodate) {
 				SetPageUptodate(page);
+				/*
+				 * It seems that there is a IO coherent bug in generic_file_mmap(),
+				 * When __do_fault() calls vma->ops->falut(filemap_fault)->aops->readpage(),
+				 * the PG_dcache_dirty is not set, so the page should be flushed (often with EXEC flags)
+				 * will not be flushed in the update_mmu_cache().
+				 *
+				 * This causes some larger ELF files failing to execute with errors like illegal instruction...
+				 *
+				 * - River.
+				 */
+				flush_dcache_page(page);
 			} else {
 				ClearPageUptodate(page);
 				SetPageError(page);