nmi_backtrace: generate one-line reports for idle cpus

[cascardo/linux.git] / lib / nmi_backtrace.c

diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c
index df347e3..7555475 100644 (file)
--- a/lib/nmi_backtrace.c
+++ b/lib/nmi_backtrace.c
@@ -16,6 +16,7 @@
 #include <linux/delay.h>
 #include <linux/kprobes.h>
 #include <linux/nmi.h>
+#include <linux/cpu.h>
 
 #ifdef arch_trigger_cpumask_backtrace
 /* For reliability, we're prepared to waste bits here. */
@@ -49,6 +50,15 @@ void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
        if (exclude_self)
                cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask));
 
+       /*
+        * Don't try to send an NMI to this cpu; it may work on some
+        * architectures, but on others it may not, and we'll get
+        * information at least as useful just by doing a dump_stack() here.
+        * Note that nmi_cpu_backtrace(NULL) will clear the cpu bit.
+        */
+       if (cpumask_test_cpu(this_cpu, to_cpumask(backtrace_mask)))
+               nmi_cpu_backtrace(NULL);
+
        if (!cpumask_empty(to_cpumask(backtrace_mask))) {
                pr_info("Sending NMI from CPU %d to CPUs %*pbl:\n",
                        this_cpu, nr_cpumask_bits, to_cpumask(backtrace_mask));
@@ -78,11 +88,16 @@ bool nmi_cpu_backtrace(struct pt_regs *regs)
        int cpu = smp_processor_id();
 
        if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
-               pr_warn("NMI backtrace for cpu %d\n", cpu);
-               if (regs)
-                       show_regs(regs);
-               else
-                       dump_stack();
+               if (regs && cpu_in_idle(instruction_pointer(regs))) {
+                       pr_warn("NMI backtrace for cpu %d skipped: idling at pc %#lx\n",
+                               cpu, instruction_pointer(regs));
+               } else {
+                       pr_warn("NMI backtrace for cpu %d\n", cpu);
+                       if (regs)
+                               show_regs(regs);
+                       else
+                               dump_stack();
+               }
                cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
                return true;
        }