From: Valentin Schneider valentin.schneider@arm.com
[ Upstream commit 0083242c93759dde353a963a90cb351c5c283379 ]
The scheduler currently expects NUMA node distances to be stable from init onwards, and as a consequence builds the related data structures once-and-for-all at init (see sched_init_numa()).
Unfortunately, on some architectures node distance is unreliable for offline nodes and may very well change upon onlining.
Skip over offline nodes during sched_init_numa(). Track nodes that have been onlined at least once, and trigger a build of a node's NUMA masks when it is first onlined post-init.
Reported-by: Geetika Moolchandani Geetika.Moolchandani1@ibm.com Signed-off-by: Srikar Dronamraju srikar@linux.vnet.ibm.com Signed-off-by: Valentin Schneider valentin.schneider@arm.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/20210818074333.48645-1-srikar@linux.vnet.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/topology.c | 65 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 65 insertions(+)
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 55a0a243e871..41f778f3db05 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -1372,6 +1372,8 @@ int sched_max_numa_distance; static int *sched_domains_numa_distance; static struct cpumask ***sched_domains_numa_masks; int __read_mostly node_reclaim_distance = RECLAIM_DISTANCE; + +static unsigned long __read_mostly *sched_numa_onlined_nodes; #endif
/* @@ -1719,6 +1721,16 @@ void sched_init_numa(void) sched_domains_numa_masks[i][j] = mask;
for_each_node(k) { + /* + * Distance information can be unreliable for + * offline nodes, defer building the node + * masks to its bringup. + * This relies on all unique distance values + * still being visible at init time. + */ + if (!node_online(j)) + continue; + if (sched_debug() && (node_distance(j, k) != node_distance(k, j))) sched_numa_warn("Node-distance not symmetric");
@@ -1772,6 +1784,53 @@ void sched_init_numa(void) sched_max_numa_distance = sched_domains_numa_distance[nr_levels - 1];
init_numa_topology_type(); + + sched_numa_onlined_nodes = bitmap_alloc(nr_node_ids, GFP_KERNEL); + if (!sched_numa_onlined_nodes) + return; + + bitmap_zero(sched_numa_onlined_nodes, nr_node_ids); + for_each_online_node(i) + bitmap_set(sched_numa_onlined_nodes, i, 1); +} + +static void __sched_domains_numa_masks_set(unsigned int node) +{ + int i, j; + + /* + * NUMA masks are not built for offline nodes in sched_init_numa(). + * Thus, when a CPU of a never-onlined-before node gets plugged in, + * adding that new CPU to the right NUMA masks is not sufficient: the + * masks of that CPU's node must also be updated. + */ + if (test_bit(node, sched_numa_onlined_nodes)) + return; + + bitmap_set(sched_numa_onlined_nodes, node, 1); + + for (i = 0; i < sched_domains_numa_levels; i++) { + for (j = 0; j < nr_node_ids; j++) { + if (!node_online(j) || node == j) + continue; + + if (node_distance(j, node) > sched_domains_numa_distance[i]) + continue; + + /* Add remote nodes in our masks */ + cpumask_or(sched_domains_numa_masks[i][node], + sched_domains_numa_masks[i][node], + sched_domains_numa_masks[0][j]); + } + } + + /* + * A new node has been brought up, potentially changing the topology + * classification. + * + * Note that this is racy vs any use of sched_numa_topology_type :/ + */ + init_numa_topology_type(); }
void sched_domains_numa_masks_set(unsigned int cpu) @@ -1779,8 +1838,14 @@ void sched_domains_numa_masks_set(unsigned int cpu) int node = cpu_to_node(cpu); int i, j;
+ __sched_domains_numa_masks_set(node); + for (i = 0; i < sched_domains_numa_levels; i++) { for (j = 0; j < nr_node_ids; j++) { + if (!node_online(j)) + continue; + + /* Set ourselves in the remote node's masks */ if (node_distance(j, node) <= sched_domains_numa_distance[i]) cpumask_set_cpu(cpu, sched_domains_numa_masks[i][j]); }