powerpc/pseries/mobility: Extend start/stop topology update scope

The powerpc mobility code may receive RTAS requests to perform PRRN
(Platform Resource Reassignment Notification) topology changes at any
time, including during LPAR migration operations.

In some configurations where the affinity of CPUs or memory is being
changed on that platform, the PRRN requests may apply or refer to
outdated information prior to the complete update of the device-tree.

This patch changes the duration for which topology updates are
suppressed during LPAR migrations from just the rtas_ibm_suspend_me()
/ 'ibm,suspend-me' call(s) to cover the entire migration_store()
operation to allow all changes to the device-tree to be applied prior
to accepting and applying any PRRN requests.

For tracking purposes, pr_info notices are added to the functions
start_topology_update() and stop_topology_update() of 'numa.c'.
Signed-off-by: Michael Bringmann <mwb@linux.vnet.ibm.com>
Reviewed-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/rtas.c

@@ -982,7 +982,6 @@ int rtas_ibm_suspend_me(u64 handle)
 	}
 
 	cpu_hotplug_disable();
-	stop_topology_update();
 
 	/* Call function on all CPUs.  One of us will make the
 	 * rtas call
@@ -995,7 +994,6 @@ int rtas_ibm_suspend_me(u64 handle)
 	if (atomic_read(&data.error) != 0)
 		printk(KERN_ERR "Error doing global join\n");
 
-	start_topology_update();
 	cpu_hotplug_enable();
 
 	/* Take down CPUs not online prior to suspend */

arch/powerpc/mm/numa.c

@@ -1521,6 +1521,10 @@ int start_topology_update(void)
 		}
 	}
 
+	pr_info("Starting topology update%s%s\n",
+		(prrn_enabled ? " prrn_enabled" : ""),
+		(vphn_enabled ? " vphn_enabled" : ""));
+
 	return rc;
 }
 
@@ -1542,6 +1546,8 @@ int stop_topology_update(void)
 		rc = del_timer_sync(&topology_timer);
 	}
 
+	pr_info("Stopping topology update\n");
+
 	return rc;
 }
 

arch/powerpc/platforms/pseries/mobility.c

@@ -360,6 +360,8 @@ static ssize_t migration_store(struct class *class,
 	if (rc)
 		return rc;
 
+	stop_topology_update();
+
 	do {
 		rc = rtas_ibm_suspend_me(streamid);
 		if (rc == -EAGAIN)
@@ -370,6 +372,9 @@ static ssize_t migration_store(struct class *class,
 		return rc;
 
 	post_mobility_fixup();
+
+	start_topology_update();
+
 	return count;
 }