Had to add get_page(cur_page); to avoid 'page dumped because: nonzero _refcount' BUG

src/lib/iov_iter.c

@@ -1205,7 +1205,7 @@ ssize_t iov_iter_get_pages(struct iov_iter *i,
 			len = maxpages * PAGE_SIZE;
 		addr &= ~(PAGE_SIZE - 1);
 		n = DIV_ROUND_UP(len, PAGE_SIZE);
-		pr_debug("iterate_iovec(), addr =0x%08lx, len=%u, n=%u, write=%u", addr, len, n, (i->type & WRITE) != WRITE);
+		pr_debug("iterate_iovec(), v.iov_base=0x%08x, addr =0x%08lx, len=%u, n=%u, write=%u", (int) v.iov_base, addr, len, n, (i->type & WRITE) != WRITE);
 		res = get_user_pages_fast(addr, n, (i->type & WRITE) != WRITE, pages);
 		if (unlikely(res < 0)) {
 			pr_debug("iterate_iovec(), res = %d", res);
@@ -1243,7 +1243,7 @@ ssize_t iov_iter_get_pages_elphel(struct iov_iter *i,
 // *** Putting temporary address here
 	struct page * cur_page = (struct page * ) circbuf0_page0;
 	addr = 0;
-
+	pr_debug("circbuf0_page0 = 0x%08x, circbuf0_page0->compound_head=0x%08lx", (int) circbuf0_page0, circbuf0_page0->compound_head );
 	len = iov->iov_len + (*start = addr & (PAGE_SIZE - 1)); // to inlude beginning of the page - for now 0;
 	if (maxsize > i->count)
 		maxsize = i->count;
@@ -1252,10 +1252,14 @@ ssize_t iov_iter_get_pages_elphel(struct iov_iter *i,
 	addr &= ~(PAGE_SIZE - 1);
 	n = DIV_ROUND_UP(len, PAGE_SIZE);
 	for (indx = 0; indx < n; indx++){
+		if ((cur_page -> compound_head) & 1){
+			pr_debug("**** COMPOUND HEAD! ****");
+		}
+		get_page(cur_page); // increments refcount
 		pages[indx] = cur_page++;
 	}
 	len -= *start;
-	pr_debug("iov_iter_get_pages_elphel()->0x%08x, n=%u", len, n);
+	pr_debug("iov_iter_get_pages_elphel()->0x%08x, n=%u, current->mm->map_count=%u", len, n, current->mm->map_count);
 	return len;
 }
 EXPORT_SYMBOL(iov_iter_get_pages_elphel);