4 files changed, 72 insertions, 62 deletions

diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index db50840e6355..6a45fb583ff1 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -46,7 +46,7 @@ static inline bool trigger_all_cpu_backtrace(void)
 #ifdef CONFIG_LOCKUP_DETECTOR
 int hw_nmi_is_cpu_stuck(struct pt_regs *);
 u64 hw_nmi_get_sample_period(int watchdog_thresh);
-extern int watchdog_enabled;
+extern int watchdog_user_enabled;
 extern int watchdog_thresh;
 struct ctl_table;
 extern int proc_dowatchdog(struct ctl_table *, int ,
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 4ce13c3cedb9..5c9e33b5c0eb 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -800,7 +800,7 @@ static struct ctl_table kern_table[] = {
 #if defined(CONFIG_LOCKUP_DETECTOR)
         {
                 .procname       = "watchdog",
-                .data           = &watchdog_enabled,
+                .data           = &watchdog_user_enabled,
                 .maxlen         = sizeof (int),
                 .mode           = 0644,
                 .proc_handler   = proc_dowatchdog,
@@ -827,7 +827,7 @@ static struct ctl_table kern_table[] = {
         },
         {
                 .procname       = "nmi_watchdog",
-                .data           = &watchdog_enabled,
+                .data           = &watchdog_user_enabled,
                 .maxlen         = sizeof (int),
                 .mode           = 0644,
                 .proc_handler   = proc_dowatchdog,
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 0cf1c1453181..69601726a745 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -178,6 +178,11 @@ static bool can_stop_full_tick(void)
          */
         if (!sched_clock_stable) {
                 trace_tick_stop(0, "unstable sched clock\n");
+                /*
+                 * Don't allow the user to think they can get
+                 * full NO_HZ with this machine.
+                 */
+                WARN_ONCE(1, "NO_HZ FULL will not work with unstable sched clock");
                 return false;
         }
 #endif
@@ -346,16 +351,6 @@ void __init tick_nohz_init(void)
         }
 
         cpu_notifier(tick_nohz_cpu_down_callback, 0);
-
-        /* Make sure full dynticks CPU are also RCU nocbs */
-        for_each_cpu(cpu, nohz_full_mask) {
-                if (!rcu_is_nocb_cpu(cpu)) {
-                        pr_warning("NO_HZ: CPU %d is not RCU nocb: "
-                                   "cleared from nohz_full range", cpu);
-                        cpumask_clear_cpu(cpu, nohz_full_mask);
-                }
-        }
-
         cpulist_scnprintf(nohz_full_buf, sizeof(nohz_full_buf), nohz_full_mask);
         pr_info("NO_HZ: Full dynticks CPUs: %s.\n", nohz_full_buf);
 }
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 05039e348f07..1241d8c91d5e 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -29,9 +29,9 @@
 #include <linux/kvm_para.h>
 #include <linux/perf_event.h>
 
-int watchdog_enabled = 1;
+int watchdog_user_enabled = 1;
 int __read_mostly watchdog_thresh = 10;
-static int __read_mostly watchdog_disabled;
+static int __read_mostly watchdog_running;
 static u64 __read_mostly sample_period;
 
 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
@@ -63,7 +63,7 @@ static int __init hardlockup_panic_setup(char *str)
         else if (!strncmp(str, "nopanic", 7))
                 hardlockup_panic = 0;
         else if (!strncmp(str, "0", 1))
-                watchdog_enabled = 0;
+                watchdog_user_enabled = 0;
         return 1;
 }
 __setup("nmi_watchdog=", hardlockup_panic_setup);
@@ -82,7 +82,7 @@ __setup("softlockup_panic=", softlockup_panic_setup);
 
 static int __init nowatchdog_setup(char *str)
 {
-        watchdog_enabled = 0;
+        watchdog_user_enabled = 0;
         return 1;
 }
 __setup("nowatchdog", nowatchdog_setup);
@@ -90,7 +90,7 @@ __setup("nowatchdog", nowatchdog_setup);
 /* deprecated */
 static int __init nosoftlockup_setup(char *str)
 {
-        watchdog_enabled = 0;
+        watchdog_user_enabled = 0;
         return 1;
 }
 __setup("nosoftlockup", nosoftlockup_setup);
@@ -158,7 +158,7 @@ void touch_all_softlockup_watchdogs(void)
 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 void touch_nmi_watchdog(void)
 {
-        if (watchdog_enabled) {
+        if (watchdog_user_enabled) {
                 unsigned cpu;
 
                 for_each_present_cpu(cpu) {
@@ -347,11 +347,6 @@ static void watchdog_enable(unsigned int cpu)
         hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
         hrtimer->function = watchdog_timer_fn;
 
-        if (!watchdog_enabled) {
-                kthread_park(current);
-                return;
-        }
-
         /* Enable the perf event */
         watchdog_nmi_enable(cpu);
 
@@ -374,6 +369,11 @@ static void watchdog_disable(unsigned int cpu)
         watchdog_nmi_disable(cpu);
 }
 
+static void watchdog_cleanup(unsigned int cpu, bool online)
+{
+        watchdog_disable(cpu);
+}
+
 static int watchdog_should_run(unsigned int cpu)
 {
         return __this_cpu_read(hrtimer_interrupts) !=
@@ -475,28 +475,40 @@ static int watchdog_nmi_enable(unsigned int cpu) { return 0; }
 static void watchdog_nmi_disable(unsigned int cpu) { return; }
 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
 
-/* prepare/enable/disable routines */
-/* sysctl functions */
-#ifdef CONFIG_SYSCTL
-static void watchdog_enable_all_cpus(void)
+static struct smp_hotplug_thread watchdog_threads = {
+        .store                  = &softlockup_watchdog,
+        .thread_should_run      = watchdog_should_run,
+        .thread_fn              = watchdog,
+        .thread_comm            = "watchdog/%u",
+        .setup                  = watchdog_enable,
+        .cleanup                = watchdog_cleanup,
+        .park                   = watchdog_disable,
+        .unpark                 = watchdog_enable,
+};
+
+static int watchdog_enable_all_cpus(void)
 {
-        unsigned int cpu;
+        int err = 0;
 
-        if (watchdog_disabled) {
-                watchdog_disabled = 0;
-                for_each_online_cpu(cpu)
-                        kthread_unpark(per_cpu(softlockup_watchdog, cpu));
+        if (!watchdog_running) {
+                err = smpboot_register_percpu_thread(&watchdog_threads);
+                if (err)
+                        pr_err("Failed to create watchdog threads, disabled\n");
+                else
+                        watchdog_running = 1;
         }
+
+        return err;
 }
 
+/* prepare/enable/disable routines */
+/* sysctl functions */
+#ifdef CONFIG_SYSCTL
 static void watchdog_disable_all_cpus(void)
 {
-        unsigned int cpu;
-
-        if (!watchdog_disabled) {
-                watchdog_disabled = 1;
-                for_each_online_cpu(cpu)
-                        kthread_park(per_cpu(softlockup_watchdog, cpu));
+        if (watchdog_running) {
+                watchdog_running = 0;
+                smpboot_unregister_percpu_thread(&watchdog_threads);
         }
 }
 
@@ -507,45 +519,48 @@ static void watchdog_disable_all_cpus(void)
 int proc_dowatchdog(struct ctl_table *table, int write,
                     void __user *buffer, size_t *lenp, loff_t *ppos)
 {
-        int ret;
+        int err, old_thresh, old_enabled;
 
-        if (watchdog_disabled < 0)
-                return -ENODEV;
+        old_thresh = ACCESS_ONCE(watchdog_thresh);
+        old_enabled = ACCESS_ONCE(watchdog_user_enabled);
 
-        ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
-        if (ret || !write)
-                return ret;
+        err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+        if (err || !write)
+                return err;
 
         set_sample_period();
         /*
          * Watchdog threads shouldn't be enabled if they are
-         * disabled. The 'watchdog_disabled' variable check in
+         * disabled. The 'watchdog_running' variable check in
          * watchdog_*_all_cpus() function takes care of this.
          */
-        if (watchdog_enabled && watchdog_thresh)
-                watchdog_enable_all_cpus();
+        if (watchdog_user_enabled && watchdog_thresh)
+                err = watchdog_enable_all_cpus();
         else
                 watchdog_disable_all_cpus();
 
-        return ret;
+        /* Restore old values on failure */
+        if (err) {
+                watchdog_thresh = old_thresh;
+                watchdog_user_enabled = old_enabled;
+        }
+
+        return err;
 }
 #endif /* CONFIG_SYSCTL */
 
-static struct smp_hotplug_thread watchdog_threads = {
-        .store                  = &softlockup_watchdog,
-        .thread_should_run      = watchdog_should_run,
-        .thread_fn              = watchdog,
-        .thread_comm            = "watchdog/%u",
-        .setup                  = watchdog_enable,
-        .park                   = watchdog_disable,
-        .unpark                 = watchdog_enable,
-};
-
 void __init lockup_detector_init(void)
 {
         set_sample_period();
-        if (smpboot_register_percpu_thread(&watchdog_threads)) {
-                pr_err("Failed to create watchdog threads, disabled\n");
-                watchdog_disabled = -ENODEV;
+
+#ifdef CONFIG_NO_HZ_FULL
+        if (watchdog_user_enabled) {
+                watchdog_user_enabled = 0;
+                pr_warning("Disabled lockup detectors by default for full dynticks\n");
+                pr_warning("You can reactivate it with 'sysctl -w kernel.watchdog=1'\n");
         }
+#endif
+
+        if (watchdog_user_enabled)
+                watchdog_enable_all_cpus();
 }