[RFC 1/4] mm, page_alloc: fix check for NULL preferred_zone

[Vlastimil Babka]

Since commit c33d6c06f60f ("mm, page_alloc: avoid looking up the first zone in
a zonelist twice") we have a wrong check for NULL preferred_zone, which can
theoretically happen due to concurrent cpuset modification. We check the
zoneref pointer which is never NULL and we should check the zone pointer.

Fixes: c33d6c06f60f ("mm, page_alloc: avoid looking up the first zone in a 
zonelist twice")
Signed-off-by: Vlastimil Babka <vba...@suse.cz>
---
 mm/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 34ada718ef47..593a11d8bc6b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3763,7 +3763,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
         */
        ac.preferred_zoneref = first_zones_zonelist(ac.zonelist,
                                        ac.high_zoneidx, ac.nodemask);
-       if (!ac.preferred_zoneref) {
+       if (!ac.preferred_zoneref->zone) {
                page = NULL;
                goto no_zone;
        }
-- 
2.11.0