7 files changed, 56 insertions, 21 deletions

diff --git a/arch/sparc/include/asm/irq_64.h b/arch/sparc/include/asm/irq_64.h
index 1934f2cbf513..a0b443cb3c1f 100644
--- a/arch/sparc/include/asm/irq_64.h
+++ b/arch/sparc/include/asm/irq_64.h
@@ -89,8 +89,8 @@ static inline unsigned long get_softint(void)
         return retval;
 }
 
-void __trigger_all_cpu_backtrace(void);
-#define trigger_all_cpu_backtrace() __trigger_all_cpu_backtrace()
+void arch_trigger_all_cpu_backtrace(void);
+#define arch_trigger_all_cpu_backtrace arch_trigger_all_cpu_backtrace
 
 extern void *hardirq_stack[NR_CPUS];
 extern void *softirq_stack[NR_CPUS];
diff --git a/arch/sparc/kernel/process_64.c b/arch/sparc/kernel/process_64.c
index 4041f94e7724..18d67854a1b8 100644
--- a/arch/sparc/kernel/process_64.c
+++ b/arch/sparc/kernel/process_64.c
@@ -251,7 +251,7 @@ static void __global_reg_poll(struct global_reg_snapshot *gp)
         }
 }
 
-void __trigger_all_cpu_backtrace(void)
+void arch_trigger_all_cpu_backtrace(void)
 {
         struct thread_info *tp = current_thread_info();
         struct pt_regs *regs = get_irq_regs();
@@ -304,7 +304,7 @@ void __trigger_all_cpu_backtrace(void)
 
 static void sysrq_handle_globreg(int key, struct tty_struct *tty)
 {
-        __trigger_all_cpu_backtrace();
+        arch_trigger_all_cpu_backtrace();
 }
 
 static struct sysrq_key_op sparc_globalreg_op = {
diff --git a/arch/x86/include/asm/nmi.h b/arch/x86/include/asm/nmi.h
index c86e5ed4af51..e63cf7d441e1 100644
--- a/arch/x86/include/asm/nmi.h
+++ b/arch/x86/include/asm/nmi.h
@@ -45,8 +45,8 @@ extern int proc_nmi_enabled(struct ctl_table *, int , struct file *,
                         void __user *, size_t *, loff_t *);
 extern int unknown_nmi_panic;
 
-void __trigger_all_cpu_backtrace(void);
-#define trigger_all_cpu_backtrace() __trigger_all_cpu_backtrace()
+void arch_trigger_all_cpu_backtrace(void);
+#define arch_trigger_all_cpu_backtrace arch_trigger_all_cpu_backtrace
 
 static inline void localise_nmi_watchdog(void)
 {
diff --git a/arch/x86/kernel/apic/nmi.c b/arch/x86/kernel/apic/nmi.c
index b3025b43b63a..db7220220d09 100644
--- a/arch/x86/kernel/apic/nmi.c
+++ b/arch/x86/kernel/apic/nmi.c
@@ -39,7 +39,7 @@
 int unknown_nmi_panic;
 int nmi_watchdog_enabled;
 
-static cpumask_var_t backtrace_mask;
+static cpumask_t backtrace_mask __read_mostly;
 
 /* nmi_active:
  * >0: the lapic NMI watchdog is active, but can be disabled
@@ -138,7 +138,6 @@ int __init check_nmi_watchdog(void)
         if (!prev_nmi_count)
                 goto error;
 
-        alloc_cpumask_var(&backtrace_mask, GFP_KERNEL|__GFP_ZERO);
         printk(KERN_INFO "Testing NMI watchdog ... ");
 
 #ifdef CONFIG_SMP
@@ -415,14 +414,17 @@ nmi_watchdog_tick(struct pt_regs *regs, unsigned reason)
         }
 
         /* We can be called before check_nmi_watchdog, hence NULL check. */
-        if (backtrace_mask != NULL && cpumask_test_cpu(cpu, backtrace_mask)) {
+        if (cpumask_test_cpu(cpu, &backtrace_mask)) {
                 static DEFINE_SPINLOCK(lock);   /* Serialise the printks */
 
                 spin_lock(&lock);
                 printk(KERN_WARNING "NMI backtrace for cpu %d\n", cpu);
+                show_regs(regs);
                 dump_stack();
                 spin_unlock(&lock);
-                cpumask_clear_cpu(cpu, backtrace_mask);
+                cpumask_clear_cpu(cpu, &backtrace_mask);
+
+                rc = 1;
         }
 
         /* Could check oops_in_progress here too, but it's safer not to */
@@ -552,14 +554,18 @@ int do_nmi_callback(struct pt_regs *regs, int cpu)
         return 0;
 }
 
-void __trigger_all_cpu_backtrace(void)
+void arch_trigger_all_cpu_backtrace(void)
 {
         int i;
 
-        cpumask_copy(backtrace_mask, cpu_online_mask);
+        cpumask_copy(&backtrace_mask, cpu_online_mask);
+
+        printk(KERN_INFO "sending NMI to all CPUs:\n");
+        apic->send_IPI_all(NMI_VECTOR);
+
         /* Wait for up to 10 seconds for all CPUs to do the backtrace */
         for (i = 0; i < 10 * 1000; i++) {
-                if (cpumask_empty(backtrace_mask))
+                if (cpumask_empty(&backtrace_mask))
                         break;
                 mdelay(1);
         }
diff --git a/drivers/char/sysrq.c b/drivers/char/sysrq.c
index 5d7a02f63e1c..50eecfe1d724 100644
--- a/drivers/char/sysrq.c
+++ b/drivers/char/sysrq.c
@@ -24,6 +24,7 @@
 #include <linux/sysrq.h>
 #include <linux/kbd_kern.h>
 #include <linux/proc_fs.h>
+#include <linux/nmi.h>
 #include <linux/quotaops.h>
 #include <linux/perf_counter.h>
 #include <linux/kernel.h>
@@ -222,12 +223,20 @@ static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus);
 
 static void sysrq_handle_showallcpus(int key, struct tty_struct *tty)
 {
-        struct pt_regs *regs = get_irq_regs();
-        if (regs) {
-                printk(KERN_INFO "CPU%d:\n", smp_processor_id());
-                show_regs(regs);
+        /*
+         * Fall back to the workqueue based printing if the
+         * backtrace printing did not succeed or the
+         * architecture has no support for it:
+         */
+        if (!trigger_all_cpu_backtrace()) {
+                struct pt_regs *regs = get_irq_regs();
+
+                if (regs) {
+                        printk(KERN_INFO "CPU%d:\n", smp_processor_id());
+                        show_regs(regs);
+                }
+                schedule_work(&sysrq_showallcpus);
         }
-        schedule_work(&sysrq_showallcpus);
 }
 
 static struct sysrq_key_op sysrq_showallcpus_op = {
diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index 29af2d5df097..b752e807adde 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -28,8 +28,23 @@ static inline void acpi_nmi_disable(void) { }
 static inline void acpi_nmi_enable(void) { }
 #endif
 
-#ifndef trigger_all_cpu_backtrace
-#define trigger_all_cpu_backtrace() do { } while (0)
+/*
+ * Create trigger_all_cpu_backtrace() out of the arch-provided
+ * base function. Return whether such support was available,
+ * to allow calling code to fall back to some other mechanism:
+ */
+#ifdef arch_trigger_all_cpu_backtrace
+static inline bool trigger_all_cpu_backtrace(void)
+{
+        arch_trigger_all_cpu_backtrace();
+
+        return true;
+}
+#else
+static inline bool trigger_all_cpu_backtrace(void)
+{
+        return false;
+}
 #endif
 
 #endif
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 7717b95c2027..9c5fa9fc57ec 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -35,6 +35,7 @@
 #include <linux/rcupdate.h>
 #include <linux/interrupt.h>
 #include <linux/sched.h>
+#include <linux/nmi.h>
 #include <asm/atomic.h>
 #include <linux/bitops.h>
 #include <linux/module.h>
@@ -469,6 +470,8 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
         }
         printk(" (detected by %d, t=%ld jiffies)\n",
                smp_processor_id(), (long)(jiffies - rsp->gp_start));
+        trigger_all_cpu_backtrace();
+
         force_quiescent_state(rsp, 0);  /* Kick them all. */
 }
 
@@ -479,12 +482,14 @@ static void print_cpu_stall(struct rcu_state *rsp)
 
         printk(KERN_ERR "INFO: RCU detected CPU %d stall (t=%lu jiffies)\n",
                         smp_processor_id(), jiffies - rsp->gp_start);
-        dump_stack();
+        trigger_all_cpu_backtrace();
+
         spin_lock_irqsave(&rnp->lock, flags);
         if ((long)(jiffies - rsp->jiffies_stall) >= 0)
                 rsp->jiffies_stall =
                         jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
         spin_unlock_irqrestore(&rnp->lock, flags);
+
         set_need_resched();  /* kick ourselves to get things going. */
 }