From bb81a09e55eaf7e5f798468ab971469b6f66a259 Mon Sep 17 00:00:00 2001
From: Andrew Morton <akpm@osdl.org>
Date: Thu, 7 Dec 2006 02:14:01 +0100
Subject: [PATCH] x86: all cpu backtrace

When a spinlock lockup occurs, arrange for the NMI code to emit an all-cpu
backtrace, so we get to see which CPU is holding the lock, and where.

Cc: Andi Kleen <ak@muc.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Andi Kleen <ak@suse.de>
---
 arch/x86_64/kernel/nmi.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

(limited to 'arch/x86_64/kernel')

diff --git a/arch/x86_64/kernel/nmi.c b/arch/x86_64/kernel/nmi.c
index 7af9cb3e2d9..27e95e7922c 100644
--- a/arch/x86_64/kernel/nmi.c
+++ b/arch/x86_64/kernel/nmi.c
@@ -12,14 +12,15 @@
  *  Mikael Pettersson	: PM converted to driver model. Disable/enable API.
  */
 
+#include <linux/nmi.h>
 #include <linux/mm.h>
 #include <linux/delay.h>
 #include <linux/interrupt.h>
 #include <linux/module.h>
 #include <linux/sysdev.h>
-#include <linux/nmi.h>
 #include <linux/sysctl.h>
 #include <linux/kprobes.h>
+#include <linux/cpumask.h>
 
 #include <asm/smp.h>
 #include <asm/nmi.h>
@@ -41,6 +42,8 @@ int panic_on_unrecovered_nmi;
 static DEFINE_PER_CPU(unsigned, perfctr_nmi_owner);
 static DEFINE_PER_CPU(unsigned, evntsel_nmi_owner[2]);
 
+static cpumask_t backtrace_mask = CPU_MASK_NONE;
+
 /* this number is calculated from Intel's MSR_P4_CRU_ESCR5 register and it's
  * offset from MSR_P4_BSU_ESCR0.  It will be the max for all platforms (for now)
  */
@@ -782,6 +785,7 @@ int __kprobes nmi_watchdog_tick(struct pt_regs * regs, unsigned reason)
 {
 	int sum;
 	int touched = 0;
+	int cpu = smp_processor_id();
 	struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);
 	u64 dummy;
 	int rc=0;
@@ -799,6 +803,16 @@ int __kprobes nmi_watchdog_tick(struct pt_regs * regs, unsigned reason)
 		touched = 1;
 	}
 
+	if (cpu_isset(cpu, backtrace_mask)) {
+		static DEFINE_SPINLOCK(lock);	/* Serialise the printks */
+
+		spin_lock(&lock);
+		printk("NMI backtrace for cpu %d\n", cpu);
+		dump_stack();
+		spin_unlock(&lock);
+		cpu_clear(cpu, backtrace_mask);
+	}
+
 #ifdef CONFIG_X86_MCE
 	/* Could check oops_in_progress here too, but it's safer
 	   not too */
@@ -931,6 +945,19 @@ int proc_nmi_enabled(struct ctl_table *table, int write, struct file *file,
 
 #endif
 
+void __trigger_all_cpu_backtrace(void)
+{
+	int i;
+
+	backtrace_mask = cpu_online_map;
+	/* Wait for up to 10 seconds for all CPUs to do the backtrace */
+	for (i = 0; i < 10 * 1000; i++) {
+		if (cpus_empty(backtrace_mask))
+			break;
+		mdelay(1);
+	}
+}
+
 EXPORT_SYMBOL(nmi_active);
 EXPORT_SYMBOL(nmi_watchdog);
 EXPORT_SYMBOL(avail_to_resrv_perfctr_nmi);
-- 
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