mm/page_alloc.c: fix regression with deferred struct page init

Commit 0e56acae4b ("mm: initialize MAX_ORDER_NR_PAGES at a time
instead of doing larger sections") is causing a regression on some
systems when the kernel is booted as Xen dom0.

The system will just hang in early boot.

Reason is an endless loop in get_page_from_freelist() in case the first
zone looked at has no free memory.  deferred_grow_zone() is always
returning true due to the following code snipplet:

  /* If the zone is empty somebody else may have cleared out the zone */
  if (!deferred_init_mem_pfn_range_in_zone(&i, zone, &spfn, &epfn,
                                           first_deferred_pfn)) {
          pgdat->first_deferred_pfn = ULONG_MAX;
          pgdat_resize_unlock(pgdat, &flags);
          return true;
  }

This in turn results in the loop as get_page_from_freelist() is assuming
forward progress can be made by doing some more struct page
initialization.

Link: http://lkml.kernel.org/r/20190620160821.4210-1-jgross@suse.com
Fixes: 0e56acae4b ("mm: initialize MAX_ORDER_NR_PAGES at a time instead of doing larger sections")
Signed-off-by: Juergen Gross <jgross@suse.com>
Suggested-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Acked-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -1826,7 +1826,8 @@ deferred_grow_zone(struct zone *zone, unsigned int order)
 						 first_deferred_pfn)) {
 		pgdat->first_deferred_pfn = ULONG_MAX;
 		pgdat_resize_unlock(pgdat, &flags);
-		return true;
+		/* Retry only once. */
+		return first_deferred_pfn != ULONG_MAX;
 	}
 
 	/*