xen/balloon: Clear PG_offline in balloon_retrieve()

Let's move the clearing to balloon_retrieve(). In
bp_state increase_reservation(), we now clear the flag a little earlier
than before, however, this should not matter for XEN.
Suggested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

drivers/xen/balloon.c

@@ -189,6 +189,7 @@ static struct page *balloon_retrieve(bool require_lowmem)
 	else
 		balloon_stats.balloon_low--;
 
+	__ClearPageOffline(page);
 	return page;
 }
 
@@ -440,7 +441,6 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
 		xenmem_reservation_va_mapping_update(1, &page, &frame_list[i]);
 
 		/* Relinquish the page back to the allocator. */
-		__ClearPageOffline(page);
 		free_reserved_page(page);
 	}
 
@@ -606,7 +606,6 @@ int alloc_xenballooned_pages(int nr_pages, struct page **pages)
 	while (pgno < nr_pages) {
 		page = balloon_retrieve(true);
 		if (page) {
-			__ClearPageOffline(page);
 			pages[pgno++] = page;
 #ifdef CONFIG_XEN_HAVE_PVMMU
 			/*