kernel/watchdog.c: perform all-CPU backtrace in case of hard lockup

[mirror_ubuntu-artful-kernel.git] / kernel / watchdog.c

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 284f0e62a927ebe0852513e53acd57296d10f262..f6b32b8cbffe297b89d0437ad387cfb36517384b 100644 (file)
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -57,8 +57,10 @@ int __read_mostly watchdog_thresh = 10;
 
 #ifdef CONFIG_SMP
 int __read_mostly sysctl_softlockup_all_cpu_backtrace;
+int __read_mostly sysctl_hardlockup_all_cpu_backtrace;
 #else
 #define sysctl_softlockup_all_cpu_backtrace 0
+#define sysctl_hardlockup_all_cpu_backtrace 0
 #endif
 static struct cpumask watchdog_cpumask __read_mostly;
 unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);
@@ -112,6 +114,7 @@ static unsigned long soft_lockup_nmi_warn;
 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 static int hardlockup_panic =
                        CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
+static unsigned long hardlockup_allcpu_dumped;
 /*
  * We may not want to enable hard lockup detection by default in all cases,
  * for example when running the kernel as a guest on a hypervisor. In these
@@ -173,6 +176,13 @@ static int __init softlockup_all_cpu_backtrace_setup(char *str)
        return 1;
 }
 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
+static int __init hardlockup_all_cpu_backtrace_setup(char *str)
+{
+       sysctl_hardlockup_all_cpu_backtrace =
+               !!simple_strtol(str, NULL, 0);
+       return 1;
+}
+__setup("hardlockup_all_cpu_backtrace=", hardlockup_all_cpu_backtrace_setup);
 #endif
 
 /*
@@ -318,17 +328,30 @@ static void watchdog_overflow_callback(struct perf_event *event,
         */
        if (is_hardlockup()) {
                int this_cpu = smp_processor_id();
+               struct pt_regs *regs = get_irq_regs();
 
                /* only print hardlockups once */
                if (__this_cpu_read(hard_watchdog_warn) == true)
                        return;
 
-               if (hardlockup_panic)
-                       panic("Watchdog detected hard LOCKUP on cpu %d",
-                             this_cpu);
+               pr_emerg("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
+               print_modules();
+               print_irqtrace_events(current);
+               if (regs)
+                       show_regs(regs);
                else
-                       WARN(1, "Watchdog detected hard LOCKUP on cpu %d",
-                            this_cpu);
+                       dump_stack();
+
+               /*
+                * Perform all-CPU dump only once to avoid multiple hardlockups
+                * generating interleaving traces
+                */
+               if (sysctl_hardlockup_all_cpu_backtrace &&
+                               !test_and_set_bit(0, &hardlockup_allcpu_dumped))
+                       trigger_allbutself_cpu_backtrace();
+
+               if (hardlockup_panic)
+                       panic("Hard LOCKUP");
 
                __this_cpu_write(hard_watchdog_warn, true);
                return;
@@ -347,6 +370,9 @@ static void watchdog_interrupt_count(void)
 static int watchdog_nmi_enable(unsigned int cpu);
 static void watchdog_nmi_disable(unsigned int cpu);
 
+static int watchdog_enable_all_cpus(void);
+static void watchdog_disable_all_cpus(void);
+
 /* watchdog kicker functions */
 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 {
@@ -651,6 +677,12 @@ static struct smp_hotplug_thread watchdog_threads = {
 
 /*
  * park all watchdog threads that are specified in 'watchdog_cpumask'
+ *
+ * This function returns an error if kthread_park() of a watchdog thread
+ * fails. In this situation, the watchdog threads of some CPUs can already
+ * be parked and the watchdog threads of other CPUs can still be runnable.
+ * Callers are expected to handle this special condition as appropriate in
+ * their context.
  */
 static int watchdog_park_threads(void)
 {
@@ -662,10 +694,6 @@ static int watchdog_park_threads(void)
                if (ret)
                        break;
        }
-       if (ret) {
-               for_each_watchdog_cpu(cpu)
-                       kthread_unpark(per_cpu(softlockup_watchdog, cpu));
-       }
        put_online_cpus();
 
        return ret;
@@ -704,6 +732,11 @@ int lockup_detector_suspend(void)
 
        if (ret == 0)
                watchdog_suspended++;
+       else {
+               watchdog_disable_all_cpus();
+               pr_err("Failed to suspend lockup detectors, disabled\n");
+               watchdog_enabled = 0;
+       }
 
        mutex_unlock(&watchdog_proc_mutex);
 
@@ -728,10 +761,17 @@ void lockup_detector_resume(void)
        mutex_unlock(&watchdog_proc_mutex);
 }
 
-static void update_watchdog_all_cpus(void)
+static int update_watchdog_all_cpus(void)
 {
-       watchdog_park_threads();
+       int ret;
+
+       ret = watchdog_park_threads();
+       if (ret)
+               return ret;
+
        watchdog_unpark_threads();
+
+       return 0;
 }
 
 static int watchdog_enable_all_cpus(void)
@@ -750,15 +790,20 @@ static int watchdog_enable_all_cpus(void)
                 * Enable/disable the lockup detectors or
                 * change the sample period 'on the fly'.
                 */
-               update_watchdog_all_cpus();
+               err = update_watchdog_all_cpus();
+
+               if (err) {
+                       watchdog_disable_all_cpus();
+                       pr_err("Failed to update lockup detectors, disabled\n");
+               }
        }
 
+       if (err)
+               watchdog_enabled = 0;
+
        return err;
 }
 
-/* prepare/enable/disable routines */
-/* sysctl functions */
-#ifdef CONFIG_SYSCTL
 static void watchdog_disable_all_cpus(void)
 {
        if (watchdog_running) {
@@ -767,6 +812,8 @@ static void watchdog_disable_all_cpus(void)
        }
 }
 
+#ifdef CONFIG_SYSCTL
+
 /*
  * Update the run state of the lockup detectors.
  */
@@ -849,12 +896,13 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write,
                } while (cmpxchg(&watchdog_enabled, old, new) != old);
 
                /*
-                * Update the run state of the lockup detectors.
-                * Restore 'watchdog_enabled' on failure.
+                * Update the run state of the lockup detectors. There is _no_
+                * need to check the value returned by proc_watchdog_update()
+                * and to restore the previous value of 'watchdog_enabled' as
+                * both lockup detectors are disabled if proc_watchdog_update()
+                * returns an error.
                 */
                err = proc_watchdog_update();
-               if (err)
-                       watchdog_enabled = old;
        }
 out:
        mutex_unlock(&watchdog_proc_mutex);