[PATCH] mm, page_alloc: fix race with cpuset update or removal

[Vlastimil Babka]

Changelog and S-O-B TBD.
---
 mm/page_alloc.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6de9440e3ae2..c397f146843a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3775,9 +3775,17 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
 	/*
 	 * Restore the original nodemask if it was potentially replaced with
 	 * &cpuset_current_mems_allowed to optimize the fast-path attempt.
+	 * Also recalculate the starting point for the zonelist iterator or
+	 * we could end up iterating over non-eligible zones endlessly.
 	 */
-	if (cpusets_enabled())
+	if (unlikely(ac.nodemask != nodemask)) {
 		ac.nodemask = nodemask;
+		ac.preferred_zoneref = first_zones_zonelist(ac.zonelist,
+						ac.high_zoneidx, ac.nodemask);
+		if (!ac.preferred_zoneref)
+			goto no_zone;
+	}
+
 	page = __alloc_pages_slowpath(alloc_mask, order, &ac);
 
 no_zone:
-- 
2.11.0