1 files changed, 39 insertions, 2 deletions

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 516203e665fc..c3319bd1b040 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -31,6 +31,12 @@
 
 int watchdog_user_enabled = 1;
 int __read_mostly watchdog_thresh = 10;
+#ifdef CONFIG_SMP
+int __read_mostly sysctl_softlockup_all_cpu_backtrace;
+#else
+#define sysctl_softlockup_all_cpu_backtrace 0
+#endif
+
 static int __read_mostly watchdog_running;
 static u64 __read_mostly sample_period;
 
@@ -47,6 +53,7 @@ static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
 static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
 #endif
+static unsigned long soft_lockup_nmi_warn;
 
 /* boot commands */
 /*
@@ -95,6 +102,15 @@ static int __init nosoftlockup_setup(char *str)
 }
 __setup("nosoftlockup", nosoftlockup_setup);
 /*  */
+#ifdef CONFIG_SMP
+static int __init softlockup_all_cpu_backtrace_setup(char *str)
+{
+        sysctl_softlockup_all_cpu_backtrace =
+                !!simple_strtol(str, NULL, 0);
+        return 1;
+}
+__setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
+#endif
 
 /*
  * Hard-lockup warnings should be triggered after just a few seconds. Soft-
@@ -271,6 +287,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
         unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
         struct pt_regs *regs = get_irq_regs();
         int duration;
+        int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
 
         /* kick the hardlockup detector */
         watchdog_interrupt_count();
@@ -317,6 +334,17 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
                 if (__this_cpu_read(soft_watchdog_warn) == true)
                         return HRTIMER_RESTART;
 
+                if (softlockup_all_cpu_backtrace) {
+                        /* Prevent multiple soft-lockup reports if one cpu is already
+                         * engaged in dumping cpu back traces
+                         */
+                        if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
+                                /* Someone else will report us. Let's give up */
+                                __this_cpu_write(soft_watchdog_warn, true);
+                                return HRTIMER_RESTART;
+                        }
+                }
+
                 printk(KERN_EMERG "BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
                         smp_processor_id(), duration,
                         current->comm, task_pid_nr(current));
@@ -327,6 +355,17 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
                 else
                         dump_stack();
 
+                if (softlockup_all_cpu_backtrace) {
+                        /* Avoid generating two back traces for current
+                         * given that one is already made above
+                         */
+                        trigger_allbutself_cpu_backtrace();
+
+                        clear_bit(0, &soft_lockup_nmi_warn);
+                        /* Barrier to sync with other cpus */
+                        smp_mb__after_atomic();
+                }
+
                 if (softlockup_panic)
                         panic("softlockup: hung tasks");
                 __this_cpu_write(soft_watchdog_warn, true);
@@ -527,10 +566,8 @@ static void update_timers_all_cpus(void)
         int cpu;
 
         get_online_cpus();
-        preempt_disable();
         for_each_online_cpu(cpu)
                 update_timers(cpu);
-        preempt_enable();
         put_online_cpus();
 }