[PATCH 3/3] sched/topology: Skip updating masks for non-online nodes

Srikar Dronamraju srikar at linux.vnet.ibm.com
Fri May 21 01:44:27 AEST 2021

Currently scheduler doesn't check if node is online before adding CPUs
to the node mask. However on some architectures, node distance is only
available for nodes that are online. Its not sure how much to rely on
the node distance, when one of the nodes is offline.

If said node distance is fake (since one of the nodes is offline) and
the actual node distance is different, then the cpumask of such nodes
when the nodes become becomes online will be wrong.

This can cause topology_span_sane to throw up a warning message and the
rest of the topology being not updated properly.

Resolve this by skipping update of cpumask for nodes that are not

Cc: LKML <linux-kernel at vger.kernel.org>
Cc: linuxppc-dev at lists.ozlabs.org
Cc: Nathan Lynch <nathanl at linux.ibm.com>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Ingo Molnar <mingo at kernel.org>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Valentin Schneider <valentin.schneider at arm.com>
Cc: Scott Cheloha <cheloha at linux.ibm.com>
Cc: Gautham R Shenoy <ego at linux.vnet.ibm.com>
Cc: Dietmar Eggemann <dietmar.eggemann at arm.com>
Cc: Mel Gorman <mgorman at techsingularity.net>
Cc: Vincent Guittot <vincent.guittot at linaro.org>
Cc: Rik van Riel <riel at surriel.com>
Cc: Geetika Moolchandani <Geetika.Moolchandani1 at ibm.com>
Reported-by: Geetika Moolchandani <Geetika.Moolchandani1 at ibm.com>
Signed-off-by: Srikar Dronamraju <srikar at linux.vnet.ibm.com>
 kernel/sched/topology.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index ccb9aff59add..ba0555e83548 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1731,6 +1731,9 @@ void sched_init_numa(void)
 			sched_domains_numa_masks[i][j] = mask;
 			for_each_node(k) {
+				if (!node_online(j))
+					continue;
 				if (sched_debug() && (node_distance(j, k) != node_distance(k, j)))
 					sched_numa_warn("Node-distance not symmetric");
@@ -1793,6 +1796,9 @@ void sched_domains_numa_masks_set(unsigned int cpu)
 	for (i = 0; i < sched_domains_numa_levels; i++) {
 		for (j = 0; j < nr_node_ids; j++) {
+			if (!node_online(j))
+				continue;
 			if (node_distance(j, node) <= sched_domains_numa_distance[i])
 				cpumask_set_cpu(cpu, sched_domains_numa_masks[i][j]);

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