[PATCH] NUMA: Early use of cpu_to_node() returns 0 instead of the correct node id

[Huang Shijie]

During the kernel booting, the generic cpu_to_node() is called too early in
arm64, powerpc and riscv when CONFIG_NUMA is enabled.

There are at least four places in the common code where
the generic cpu_to_node() is called before it is initialized:
	   1.) early_trace_init()         in kernel/trace/trace.c
	   2.) sched_init()               in kernel/sched/core.c
	   3.) init_sched_fair_class()    in kernel/sched/fair.c
	   4.) workqueue_init_early()     in kernel/workqueue.c

In order to fix the bug, the patch changes generic cpu_to_node to
function pointer, and export it for kernel modules.
Introduce smp_prepare_boot_cpu_start() to wrap the original
smp_prepare_boot_cpu(), and set cpu_to_node with early_cpu_to_node.
Introduce smp_prepare_cpus_done() to wrap the original smp_prepare_cpus(),
and set the cpu_to_node to formal _cpu_to_node().

Signed-off-by: Huang Shijie <shijie@xxxxxxxxxxxxxxxxxxxxxx>
---
 drivers/base/arch_numa.c | 11 +++++++++++
 include/linux/topology.h |  6 ++----
 init/main.c              | 29 +++++++++++++++++++++++++++--
 3 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/drivers/base/arch_numa.c b/drivers/base/arch_numa.c
index 5b59d133b6af..867a477fa975 100644
--- a/drivers/base/arch_numa.c
+++ b/drivers/base/arch_numa.c
@@ -61,6 +61,17 @@ EXPORT_SYMBOL(cpumask_of_node);
 
 #endif
 
+#ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID
+#ifndef cpu_to_node
+int _cpu_to_node(int cpu)
+{
+	return per_cpu(numa_node, cpu);
+}
+int (*cpu_to_node)(int cpu);
+EXPORT_SYMBOL(cpu_to_node);
+#endif
+#endif
+
 static void numa_update_cpu(unsigned int cpu, bool remove)
 {
 	int nid = cpu_to_node(cpu);
diff --git a/include/linux/topology.h b/include/linux/topology.h
index 52f5850730b3..e7ce2bae11dd 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -91,10 +91,8 @@ static inline int numa_node_id(void)
 #endif
 
 #ifndef cpu_to_node
-static inline int cpu_to_node(int cpu)
-{
-	return per_cpu(numa_node, cpu);
-}
+extern int (*cpu_to_node)(int cpu);
+extern int _cpu_to_node(int cpu);
 #endif
 
 #ifndef set_numa_node
diff --git a/init/main.c b/init/main.c
index e24b0780fdff..b142e9c51161 100644
--- a/init/main.c
+++ b/init/main.c
@@ -870,6 +870,18 @@ static void __init print_unknown_bootoptions(void)
 	memblock_free(unknown_options, len);
 }
 
+static void __init smp_prepare_boot_cpu_start(void)
+{
+	smp_prepare_boot_cpu();	/* arch-specific boot-cpu hooks */
+
+#ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID
+#ifndef cpu_to_node
+	/* The early_cpu_to_node should be ready now. */
+	cpu_to_node = early_cpu_to_node;
+#endif
+#endif
+}
+
 asmlinkage __visible __init __no_sanitize_address __noreturn __no_stack_protector
 void start_kernel(void)
 {
@@ -899,7 +911,7 @@ void start_kernel(void)
 	setup_command_line(command_line);
 	setup_nr_cpu_ids();
 	setup_per_cpu_areas();
-	smp_prepare_boot_cpu();	/* arch-specific boot-cpu hooks */
+	smp_prepare_boot_cpu_start();
 	boot_cpu_hotplug_init();
 
 	pr_notice("Kernel command line: %s\n", saved_command_line);
@@ -1519,6 +1531,19 @@ void __init console_on_rootfs(void)
 	fput(file);
 }
 
+static void __init smp_prepare_cpus_done(unsigned int setup_max_cpus)
+{
+	/* Different ARCHs may override smp_prepare_cpus() */
+	smp_prepare_cpus(setup_max_cpus);
+
+#ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID
+#ifndef cpu_to_node
+	/* Change to the formal function. */
+	cpu_to_node = _cpu_to_node;
+#endif
+#endif
+}
+
 static noinline void __init kernel_init_freeable(void)
 {
 	/* Now the scheduler is fully set up and can do blocking allocations */
@@ -1531,7 +1556,7 @@ static noinline void __init kernel_init_freeable(void)
 
 	cad_pid = get_pid(task_pid(current));
 
-	smp_prepare_cpus(setup_max_cpus);
+	smp_prepare_cpus_done(setup_max_cpus);
 
 	workqueue_init();
 
-- 
2.40.1