Subject: [PATCH AUTOSEL 4.9 06/66] powerpc/pseries: Disable CPU hotplug across migrations

From: Sasha Levin <[email-masked]>
Date: Sat, 9 Nov 2019 21:47:45 -0500

From: Nathan Fontenot <[email-masked]>

[ Upstream commit 85a88cabad57d26d826dd94ea34d3a785824d802 ]

When performing partition migrations all present CPUs must be online
as all present CPUs must make the H_JOIN call as part of the migration
process. Once all present CPUs make the H_JOIN call, one CPU is returned
to make the rtas call to perform the migration to the destination system.

During testing of migration and changing the SMT state we have found
instances where CPUs are offlined, as part of the SMT state change,
before they make the H_JOIN call. This results in a hung system where
every CPU is either in H_JOIN or offline.

To prevent this this patch disables CPU hotplug during the migration
process.

Signed-off-by: Nathan Fontenot <[email-masked]>
Reviewed-by: Tyrel Datwyler <[email-masked]>
Signed-off-by: Michael Ellerman <[email-masked]>
Signed-off-by: Sasha Levin <[email-masked]>
---
 arch/powerpc/kernel/rtas.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index a309a7a29cc60..641f3e4c33808 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -984,6 +984,7 @@ int rtas_ibm_suspend_me(u64 handle)
 		goto out;
 	}
 
+	cpu_hotplug_disable();
 	stop_topology_update();
 
 	/* Call function on all CPUs.  One of us will make the
@@ -998,6 +999,7 @@ int rtas_ibm_suspend_me(u64 handle)
 		printk(KERN_ERR "Error doing global join\n");
 
 	start_topology_update();
+	cpu_hotplug_enable();
 
 	/* Take down CPUs not online prior to suspend */
 	cpuret = rtas_offline_cpus_mask(offline_mask);
-- 
2.20.1