[PATCH v03] powerpc/numa: Perform full re-add of CPU for PRRN/VPHN topology update

[Michael Bringmann]

On pseries systems, performing changes to a partition's affinity
can result in altering the nodes a CPU is assigned to the
current system.  For example, some systems are subject to resource
balancing operations by the operator or control software.  In such
environments, system CPUs may be in node 1 and 3 at boot, and be
moved to nodes 2, 3, and 5, for better performance.

The current implementation attempts to recognize such changes within
the powerpc-specific version of arch_update_cpu_topology to modify a
range of system data structures directly.  However, some scheduler
data structures may be inaccessible, or the timing of a node change
may still lead to corruption or error in other modules (e.g. user
space) which do not receive notification of these changes.

This patch modifies the PRRN/VPHN topology update worker function to
recognize an affinity change for a CPU, and to perform a full DLPAR
remove and add of the CPU instead of dynamically changing its node
to resolve this issue.

[Based upon patch submission:
Subject: [PATCH] powerpc/pseries: Perform full re-add of CPU for topology update post-migration
From: Nathan Fontenot <nfont@xxxxxxxxxxxxxxxxxx>
Date: Tue Oct 30 05:43:36 AEDT 2018
]

[Replace patch submission:
Subject: [PATCH] powerpc/topology: Update numa mask when cpu node mapping changes
From: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
Date: Wed Oct 10 15:24:46 AEDT 2018
]

Signed-off-by: Michael Bringmann <mwb@xxxxxxxxxxxxxxxxxx>
---
Changes in v03:
  -- Fixed under-scheduling of topo updates.
Changes in v02:
  -- Reuse more of the previous implementation to reduce patch size
  -- Replace former calls to numa_update_cpu_topology(false) by
     topology_schedule_update
  -- Make sure that we report topology changes back through
     arch_update_cpu_topology
  -- Fix problem observed in powerpc next kernel with updating
     cpu_associativity_changes_mask in timer_topology_fn when both
     prrn_enabled and vphn_enabled, and many extra CPUs are possible,
     but not installed.
  -- Fix problem with updating cpu_associativity_changes_mask when
     VPHN associativity information does not arrive until after first
     call to update topology occurs.
---
 arch/powerpc/include/asm/topology.h |    7 +---
 arch/powerpc/kernel/rtasd.c         |    2 +
 arch/powerpc/mm/numa.c              |   69 +++++++++++++++++++++++------------
 3 files changed, 48 insertions(+), 30 deletions(-)

diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
index f85e2b0..79505c3 100644
--- a/arch/powerpc/include/asm/topology.h
+++ b/arch/powerpc/include/asm/topology.h
@@ -42,7 +42,7 @@ static inline int pcibus_to_node(struct pci_bus *bus)
 
 extern int sysfs_add_device_to_node(struct device *dev, int nid);
 extern void sysfs_remove_device_from_node(struct device *dev, int nid);
-extern int numa_update_cpu_topology(bool cpus_locked);
+extern void topology_schedule_update(void);
 
 static inline void update_numa_cpu_lookup_table(unsigned int cpu, int node)
 {
@@ -77,10 +77,7 @@ static inline void sysfs_remove_device_from_node(struct device *dev,
 {
 }
 
-static inline int numa_update_cpu_topology(bool cpus_locked)
-{
-	return 0;
-}
+static inline void topology_schedule_update(void) {}
 
 static inline void update_numa_cpu_lookup_table(unsigned int cpu, int node) {}
 
diff --git a/arch/powerpc/kernel/rtasd.c b/arch/powerpc/kernel/rtasd.c
index 8a1746d..b1828de 100644
--- a/arch/powerpc/kernel/rtasd.c
+++ b/arch/powerpc/kernel/rtasd.c
@@ -285,7 +285,7 @@ static void handle_prrn_event(s32 scope)
 	 * the RTAS event.
 	 */
 	pseries_devicetree_update(-scope);
-	numa_update_cpu_topology(false);
+	topology_schedule_update();
 }
 
 static void handle_rtas_event(const struct rtas_error_log *log)
diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index ef6bdf1..a750ec0 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -1077,6 +1077,9 @@ struct topology_update_data {
 static void reset_topology_timer(void);
 static int topology_timer_secs = 1;
 static int topology_inited;
+static int topology_update_in_progress;
+static int topology_changed;
+static unsigned long topology_scans;
 
 /*
  * Change polling interval for associativity changes.
@@ -1297,9 +1300,9 @@ static int update_lookup_table(void *data)
  * Update the node maps and sysfs entries for each cpu whose home node
  * has changed. Returns 1 when the topology has changed, and 0 otherwise.
  *
- * cpus_locked says whether we already hold cpu_hotplug_lock.
+ * readd_cpus: Also readd any CPUs that have changed affinity
  */
-int numa_update_cpu_topology(bool cpus_locked)
+static int numa_update_cpu_topology(bool readd_cpus)
 {
 	unsigned int cpu, sibling, changed = 0;
 	struct topology_update_data *updates, *ud;
@@ -1307,7 +1310,8 @@ int numa_update_cpu_topology(bool cpus_locked)
 	struct device *dev;
 	int weight, new_nid, i = 0;
 
-	if (!prrn_enabled && !vphn_enabled && topology_inited)
+	if ((!prrn_enabled && !vphn_enabled && topology_inited) ||
+		topology_update_in_progress)
 		return 0;
 
 	weight = cpumask_weight(&cpu_associativity_changes_mask);
@@ -1318,6 +1322,8 @@ int numa_update_cpu_topology(bool cpus_locked)
 	if (!updates)
 		return 0;
 
+	topology_update_in_progress = 1;
+
 	cpumask_clear(&updated_cpus);
 
 	for_each_cpu(cpu, &cpu_associativity_changes_mask) {
@@ -1339,16 +1345,21 @@ int numa_update_cpu_topology(bool cpus_locked)
 
 		new_nid = find_and_online_cpu_nid(cpu);
 
-		if (new_nid == numa_cpu_lookup_table[cpu]) {
+		if ((new_nid == numa_cpu_lookup_table[cpu]) ||
+			!cpu_present(cpu)) {
 			cpumask_andnot(&cpu_associativity_changes_mask,
 					&cpu_associativity_changes_mask,
 					cpu_sibling_mask(cpu));
-			dbg("Assoc chg gives same node %d for cpu%d\n",
+			if (cpu_present(cpu))
+				dbg("Assoc chg gives same node %d for cpu%d\n",
 					new_nid, cpu);
 			cpu = cpu_last_thread_sibling(cpu);
 			continue;
 		}
 
+		if (readd_cpus)
+			dlpar_cpu_readd(cpu);
+
 		for_each_cpu(sibling, cpu_sibling_mask(cpu)) {
 			ud = &updates[i++];
 			ud->next = &updates[i];
@@ -1390,23 +1401,15 @@ int numa_update_cpu_topology(bool cpus_locked)
 	if (!cpumask_weight(&updated_cpus))
 		goto out;
 
-	if (cpus_locked)
-		stop_machine_cpuslocked(update_cpu_topology, &updates[0],
-					&updated_cpus);
-	else
-		stop_machine(update_cpu_topology, &updates[0], &updated_cpus);
+	stop_machine(update_cpu_topology, &updates[0], &updated_cpus);
 
 	/*
 	 * Update the numa-cpu lookup table with the new mappings, even for
 	 * offline CPUs. It is best to perform this update from the stop-
 	 * machine context.
 	 */
-	if (cpus_locked)
-		stop_machine_cpuslocked(update_lookup_table, &updates[0],
-					cpumask_of(raw_smp_processor_id()));
-	else
-		stop_machine(update_lookup_table, &updates[0],
-			     cpumask_of(raw_smp_processor_id()));
+	stop_machine(update_lookup_table, &updates[0],
+		     cpumask_of(raw_smp_processor_id()));
 
 	for (ud = &updates[0]; ud; ud = ud->next) {
 		unregister_cpu_under_node(ud->cpu, ud->old_nid);
@@ -1420,35 +1423,53 @@ int numa_update_cpu_topology(bool cpus_locked)
 	}
 
 out:
+	topology_changed = changed;
+	topology_update_in_progress = 0;
 	kfree(updates);
 	return changed;
 }
 
 int arch_update_cpu_topology(void)
 {
-	return numa_update_cpu_topology(true);
+	int changed = topology_changed;
+
+	topology_changed = 0;
+	return changed;
 }
 
 static void topology_work_fn(struct work_struct *work)
 {
-	rebuild_sched_domains();
+	lock_device_hotplug();
+	if (numa_update_cpu_topology(true))
+		rebuild_sched_domains();
+	unlock_device_hotplug();
 }
 static DECLARE_WORK(topology_work, topology_work_fn);
 
-static void topology_schedule_update(void)
+void topology_schedule_update(void)
 {
-	schedule_work(&topology_work);
+	if (!topology_update_in_progress)
+		schedule_work(&topology_work);
 }
 
 static void topology_timer_fn(struct timer_list *unused)
 {
+	bool sdo = false;
+
+	if (topology_scans < 1)
+		bitmap_fill(cpumask_bits(&cpu_associativity_changes_mask),
+			    nr_cpumask_bits);
+
 	if (prrn_enabled && cpumask_weight(&cpu_associativity_changes_mask))
-		topology_schedule_update();
-	else if (vphn_enabled) {
+		sdo =  true;
+	if (vphn_enabled) {
 		if (update_cpu_associativity_changes_mask() > 0)
-			topology_schedule_update();
+			sdo =  true;
 		reset_topology_timer();
 	}
+	if (sdo)
+		topology_schedule_update();
+	topology_scans++;
 }
 static struct timer_list topology_timer;
 
@@ -1561,7 +1582,7 @@ void __init shared_proc_topology_init(void)
 	if (lppaca_shared_proc(get_lppaca())) {
 		bitmap_fill(cpumask_bits(&cpu_associativity_changes_mask),
 			    nr_cpumask_bits);
-		numa_update_cpu_topology(false);
+		topology_schedule_update();
 	}
 }