[PATCH 1/2] nmi: Export CPU backtrace APIs for loadable modules

[Mayank Rungta via B4 Relay <devnull+mrungta.google.com@kernel.org>]

From: Mayank Rungta <mrungta@google.com>

Currently, CPU backtrace functions cannot be called from loadable
modules because the underlying helper arch_trigger_cpumask_backtrace()
is not exported.

Instead of exporting arch_trigger_cpumask_backtrace() individually
across every supported architecture, introduce and export a common
helper, cpumask_backtrace(), in lib/nmi_backtrace.c. Update the four
inline CPU backtrace macros in include/linux/nmi.h to route through this
centralized helper.

Signed-off-by: Mayank Rungta <mrungta@google.com>
---
 include/linux/nmi.h | 10 ++++++----
 lib/nmi_backtrace.c |  7 +++++++
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index 89c5465e2524..af69712df5f4 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -157,27 +157,29 @@ static inline void touch_nmi_watchdog(void)
  * to allow calling code to fall back to some other mechanism:
  */
 #ifdef arch_trigger_cpumask_backtrace
+void cpumask_backtrace(const cpumask_t *mask, int exclude_cpu);
+
 static inline bool trigger_all_cpu_backtrace(void)
 {
-	arch_trigger_cpumask_backtrace(cpu_online_mask, -1);
+	cpumask_backtrace(cpu_online_mask, -1);
 	return true;
 }
 
 static inline bool trigger_allbutcpu_cpu_backtrace(int exclude_cpu)
 {
-	arch_trigger_cpumask_backtrace(cpu_online_mask, exclude_cpu);
+	cpumask_backtrace(cpu_online_mask, exclude_cpu);
 	return true;
 }
 
 static inline bool trigger_cpumask_backtrace(struct cpumask *mask)
 {
-	arch_trigger_cpumask_backtrace(mask, -1);
+	cpumask_backtrace(mask, -1);
 	return true;
 }
 
 static inline bool trigger_single_cpu_backtrace(int cpu)
 {
-	arch_trigger_cpumask_backtrace(cpumask_of(cpu), -1);
+	cpumask_backtrace(cpumask_of(cpu), -1);
 	return true;
 }
 
diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c
index a3bfa9360b23..f39c9eca8888 100644
--- a/lib/nmi_backtrace.c
+++ b/lib/nmi_backtrace.c
@@ -19,6 +19,7 @@
 #include <linux/stringify.h>
 #include <linux/nmi.h>
 #include <linux/cpu.h>
+#include <linux/export.h>
 #include <linux/sched/debug.h>
 
 #ifdef arch_trigger_cpumask_backtrace
@@ -129,4 +130,10 @@ bool nmi_cpu_backtrace(struct pt_regs *regs)
 	return false;
 }
 NOKPROBE_SYMBOL(nmi_cpu_backtrace);
+
+void cpumask_backtrace(const cpumask_t *mask, int exclude_cpu)
+{
+	arch_trigger_cpumask_backtrace(mask, exclude_cpu);
+}
+EXPORT_SYMBOL_GPL(cpumask_backtrace);
 #endif

-- 
2.55.0.508.g3f0d502094-goog