[V8,3/3] hotplug/cpu: Fix crash with memoryless nodes

Message ID 55ff4b6a-7f43-e171-d214-cf10d466aa71@linux.vnet.ibm.com
State New
Headers show
  • powerpc/nodes: Fix issues with memoryless nodes
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Commit Message

Michael Bringmann Nov. 28, 2017, 10:58 p.m.
On powerpc systems with shared configurations of CPUs and memory and
memoryless nodes at boot, an event ordering problem was observed on
a SLES12 build platforms with the hot-add of CPUs to the memoryless

* The most common error occurred when the memory SLAB driver attempted
  to reference the memoryless node to which a CPU was being added
  before the kernel had finished initializing all of the data structures
  for the CPU and exited 'device_online' under DLPAR/hot-add.

  Normally the memoryless node would be initialized through the call
  path device_online ... arch_update_cpu_topology ... find_cpu_nid
  ...  try_online_node.  This patch ensures that the powerpc node will
  be initialized as early as possible, even if it was memoryless and
  CPU-less at the point when we are trying to hot-add a new CPU to it.

Signed-off-by: Michael Bringmann <mwb@linux.vnet.ibm.com>
Changes in V8:
  -- Change a 'printk(KERN_INFO ...)' statement to be a pr_debug()
  -- Rename 'find_cpu_nid' to 'find_and_online_cpu_nid' for better
     clarity of its function.
 arch/powerpc/mm/numa.c                       |    4 +++-
 arch/powerpc/platforms/pseries/hotplug-cpu.c |    3 +++
 2 files changed, 6 insertions(+), 1 deletion(-)


diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 6b08dd8..a182f9e 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -1307,7 +1307,7 @@  static long vphn_get_associativity(unsigned long cpu,
 	return rc;
-static inline int find_and_online_cpu_nid(int cpu)
+int find_and_online_cpu_nid(int cpu)
 	__be32 associativity[VPHN_ASSOC_BUFSIZE] = {0};
 	int new_nid;
@@ -1340,6 +1340,8 @@  static inline int find_and_online_cpu_nid(int cpu)
+	pr_debug("%s:%d cpu %d nid %d\n", __FUNCTION__, __LINE__,
+		cpu, new_nid);
 	return new_nid;
diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c
index a7d14aa7..dceb514 100644
--- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
+++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c
@@ -340,6 +340,8 @@  static void pseries_remove_processor(struct device_node *np)
+extern int find_and_online_cpu_nid(int cpu);
 static int dlpar_online_cpu(struct device_node *dn)
 	int rc = 0;
@@ -364,6 +366,7 @@  static int dlpar_online_cpu(struct device_node *dn)
+			find_and_online_cpu_nid(cpu);
 			rc = device_online(get_cpu_device(cpu));
 			if (rc)
 				goto out;