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

From	Vlastimil Babka <vbabka@suse.cz>
Newsgroups	linux.kernel
Subject	[RFC 1/4] mm, page_alloc: fix check for NULL preferred_zone
Date	2017-01-18 01:10 +0100
Message-ID	<t0LZ8-5nf-31@gated-at.bofh.it> (permalink)
References	<t0LZ8-5nf-33@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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 <vbabka@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

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[RFC 1/4] mm, page_alloc: fix check for NULL preferred_zone Vlastimil Babka <vbabka@suse.cz> - 2017-01-18 01:10 +0100
  Re: [RFC 1/4] mm, page_alloc: fix check for NULL preferred_zone Michal Hocko <mhocko@kernel.org> - 2017-01-18 10:40 +0100
    Re: [RFC 1/4] mm, page_alloc: fix check for NULL preferred_zone Vlastimil Babka <vbabka@suse.cz> - 2017-01-18 10:50 +0100
      Re: [RFC 1/4] mm, page_alloc: fix check for NULL preferred_zone Michal Hocko <mhocko@kernel.org> - 2017-01-18 11:20 +0100
  Re: [RFC 1/4] mm, page_alloc: fix check for NULL preferred_zone Mel Gorman <mgorman@techsingularity.net> - 2017-01-18 10:50 +0100

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