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 26caf51..7555475 100644 (file)
--- a/lib/nmi_backtrace.c
+++ b/lib/nmi_backtrace.c
@@ -16,21 +16,23 @@
 #include <linux/delay.h>
 #include <linux/kprobes.h>
 #include <linux/nmi.h>
+#include <linux/cpu.h>
 
-#ifdef arch_trigger_all_cpu_backtrace
+#ifdef arch_trigger_cpumask_backtrace
 /* For reliability, we're prepared to waste bits here. */
 static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
 
-/* "in progress" flag of arch_trigger_all_cpu_backtrace */
+/* "in progress" flag of arch_trigger_cpumask_backtrace */
 static unsigned long backtrace_flag;
 
 /*
- * When raise() is called it will be is passed a pointer to the
+ * When raise() is called it will be passed a pointer to the
  * backtrace_mask. Architectures that call nmi_cpu_backtrace()
  * directly from their raise() functions may rely on the mask
  * they are passed being updated as a side effect of this call.
  */
-void nmi_trigger_all_cpu_backtrace(bool include_self,
+void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
+                                  bool exclude_self,
                                   void (*raise)(cpumask_t *mask))
 {
        int i, this_cpu = get_cpu();
@@ -44,13 +46,22 @@ void nmi_trigger_all_cpu_backtrace(bool include_self,
                return;
        }
 
-       cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask);
-       if (!include_self)
+       cpumask_copy(to_cpumask(backtrace_mask), 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 to %s CPUs:\n",
-                       (include_self ? "all" : "other"));
+               pr_info("Sending NMI from CPU %d to CPUs %*pbl:\n",
+                       this_cpu, nr_cpumask_bits, to_cpumask(backtrace_mask));
                raise(to_cpumask(backtrace_mask));
        }
 
@@ -77,11 +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;
        }