debug: softlockup looping fix

Rafael J. Wysocki reported weird, multi-seconds delays during
suspend/resume and bisected it back to:

  commit 82a1fcb90287052aabfa235e7ffc693ea003fe69
  Author: Ingo Molnar <mingo@elte.hu>
  Date:   Fri Jan 25 21:08:02 2008 +0100

      softlockup: automatically detect hung TASK_UNINTERRUPTIBLE tasks

fix it:

 - restore the old wakeup mechanism
 - fix break usage in do_each_thread() { } while_each_thread().
 - fix the hotplug switch stmt, a fall-through case was broken.

Bisected-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 20 insertions, 10 deletions

diff --git a/kernel/softlockup.c b/kernel/softlockup.c
index c1d76552446e..7c2da88db4ed 100644
--- a/kernel/softlockup.c
+++ b/kernel/softlockup.c
@@ -101,6 +101,10 @@ void softlockup_tick(void)
 
         now = get_timestamp(this_cpu);
 
+        /* Wake up the high-prio watchdog task every second: */
+        if (now > (touch_timestamp + 1))
+                wake_up_process(per_cpu(watchdog_task, this_cpu));
+
         /* Warn about unreasonable delays: */
         if (now <= (touch_timestamp + softlockup_thresh))
                 return;
@@ -191,11 +195,11 @@ static void check_hung_uninterruptible_tasks(int this_cpu)
         read_lock(&tasklist_lock);
         do_each_thread(g, t) {
                 if (!--max_count)
-                        break;
+                        goto unlock;
                 if (t->state & TASK_UNINTERRUPTIBLE)
                         check_hung_task(t, now);
         } while_each_thread(g, t);
-
+ unlock:
         read_unlock(&tasklist_lock);
 }
 
@@ -218,14 +222,19 @@ static int watchdog(void *__bind_cpu)
          * debug-printout triggers in softlockup_tick().
          */
         while (!kthread_should_stop()) {
+                set_current_state(TASK_INTERRUPTIBLE);
                 touch_softlockup_watchdog();
-                msleep_interruptible(10000);
+                schedule();
+
+                if (kthread_should_stop())
+                        break;
 
                 if (this_cpu != check_cpu)
                         continue;
 
                 if (sysctl_hung_task_timeout_secs)
                         check_hung_uninterruptible_tasks(this_cpu);
+
         }
 
         return 0;
@@ -259,13 +268,6 @@ cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
                 wake_up_process(per_cpu(watchdog_task, hotcpu));
                 break;
 #ifdef CONFIG_HOTPLUG_CPU
-        case CPU_UP_CANCELED:
-        case CPU_UP_CANCELED_FROZEN:
-                if (!per_cpu(watchdog_task, hotcpu))
-                        break;
-                /* Unbind so it can run.  Fall thru. */
-                kthread_bind(per_cpu(watchdog_task, hotcpu),
-                             any_online_cpu(cpu_online_map));
         case CPU_DOWN_PREPARE:
         case CPU_DOWN_PREPARE_FROZEN:
                 if (hotcpu == check_cpu) {
@@ -275,6 +277,14 @@ cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
                         check_cpu = any_online_cpu(temp_cpu_online_map);
                 }
                 break;
+
+        case CPU_UP_CANCELED:
+        case CPU_UP_CANCELED_FROZEN:
+                if (!per_cpu(watchdog_task, hotcpu))
+                        break;
+                /* Unbind so it can run.  Fall thru. */
+                kthread_bind(per_cpu(watchdog_task, hotcpu),
+                             any_online_cpu(cpu_online_map));
         case CPU_DEAD:
         case CPU_DEAD_FROZEN:
                 p = per_cpu(watchdog_task, hotcpu);