On 01/18/2017 10:31 AM, Michal Hocko wrote:
On Tue 17-01-17 23:16:07, Vlastimil Babka wrote: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@xxxxxxx> --- 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) {When can the ->zone be NULL?
Either we get a genuinely screwed nodemask, or there's a concurrent cpuset update and nodes in zonelist are ordered in such a way that we see all of them as not being available to us in the nodemask/current->mems_alowed, when we iterate the zonelist, so we reach the end of zonelist. The zonelists are terminated with a zoneref with NULL zone pointer.
page = NULL; goto no_zone; } -- 2.11.0
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