softlockup: decouple hung tasks check from softlockup detection

Decoupling allows:

* hung tasks check to happen at very low priority

* hung tasks check and softlockup to be enabled/disabled independently
  at compile and/or run-time

* individual panic settings to be enabled disabled independently
  at compile and/or run-time

* softlockup threshold to be reduced without increasing hung tasks
  poll frequency (hung task check is expensive relative to softlock watchdog)

* hung task check to be zero over-head when disabled at run-time

Signed-off-by: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 0 insertions, 100 deletions

diff --git a/kernel/softlockup.c b/kernel/softlockup.c
index 85d5a2455103..88796c330838 100644
--- a/kernel/softlockup.c
+++ b/kernel/softlockup.c
@@ -166,97 +166,11 @@ void softlockup_tick(void)
 }
 
 /*
- * Have a reasonable limit on the number of tasks checked:
- */
-unsigned long __read_mostly sysctl_hung_task_check_count = 1024;
-
-/*
- * Zero means infinite timeout - no checking done:
- */
-unsigned long __read_mostly sysctl_hung_task_timeout_secs = 480;
-
-unsigned long __read_mostly sysctl_hung_task_warnings = 10;
-
-/*
- * Only do the hung-tasks check on one CPU:
- */
-static int check_cpu __read_mostly = -1;
-
-static void check_hung_task(struct task_struct *t, unsigned long now)
-{
-        unsigned long switch_count = t->nvcsw + t->nivcsw;
-
-        if (t->flags & PF_FROZEN)
-                return;
-
-        if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
-                t->last_switch_count = switch_count;
-                t->last_switch_timestamp = now;
-                return;
-        }
-        if ((long)(now - t->last_switch_timestamp) <
-                                        sysctl_hung_task_timeout_secs)
-                return;
-        if (!sysctl_hung_task_warnings)
-                return;
-        sysctl_hung_task_warnings--;
-
-        /*
-         * Ok, the task did not get scheduled for more than 2 minutes,
-         * complain:
-         */
-        printk(KERN_ERR "INFO: task %s:%d blocked for more than "
-                        "%ld seconds.\n", t->comm, t->pid,
-                        sysctl_hung_task_timeout_secs);
-        printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
-                        " disables this message.\n");
-        sched_show_task(t);
-        __debug_show_held_locks(t);
-
-        t->last_switch_timestamp = now;
-        touch_nmi_watchdog();
-
-        if (softlockup_panic)
-                panic("softlockup: blocked tasks");
-}
-
-/*
- * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
- * a really long time (120 seconds). If that happens, print out
- * a warning.
- */
-static void check_hung_uninterruptible_tasks(int this_cpu)
-{
-        int max_count = sysctl_hung_task_check_count;
-        unsigned long now = get_timestamp(this_cpu);
-        struct task_struct *g, *t;
-
-        /*
-         * If the system crashed already then all bets are off,
-         * do not report extra hung tasks:
-         */
-        if (test_taint(TAINT_DIE) || did_panic)
-                return;
-
-        read_lock(&tasklist_lock);
-        do_each_thread(g, t) {
-                if (!--max_count)
-                        goto unlock;
-                /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
-                if (t->state == TASK_UNINTERRUPTIBLE)
-                        check_hung_task(t, now);
-        } while_each_thread(g, t);
- unlock:
-        read_unlock(&tasklist_lock);
-}
-
-/*
  * The watchdog thread - runs every second and touches the timestamp.
  */
 static int watchdog(void *__bind_cpu)
 {
         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
-        int this_cpu = (long)__bind_cpu;
 
         sched_setscheduler(current, SCHED_FIFO, &param);
 
@@ -276,11 +190,6 @@ static int watchdog(void *__bind_cpu)
                 if (kthread_should_stop())
                         break;
 
-                if (this_cpu == check_cpu) {
-                        if (sysctl_hung_task_timeout_secs)
-                                check_hung_uninterruptible_tasks(this_cpu);
-                }
-
                 set_current_state(TASK_INTERRUPTIBLE);
         }
         __set_current_state(TASK_RUNNING);
@@ -312,18 +221,9 @@ cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
                 break;
         case CPU_ONLINE:
         case CPU_ONLINE_FROZEN:
-                check_cpu = cpumask_any(cpu_online_mask);
                 wake_up_process(per_cpu(watchdog_task, hotcpu));
                 break;
 #ifdef CONFIG_HOTPLUG_CPU
-        case CPU_DOWN_PREPARE:
-        case CPU_DOWN_PREPARE_FROZEN:
-                if (hotcpu == check_cpu) {
-                        /* Pick any other online cpu. */
-                        check_cpu = cpumask_any_but(cpu_online_mask, hotcpu);
-                }
-                break;
-
         case CPU_UP_CANCELED:
         case CPU_UP_CANCELED_FROZEN:
                 if (!per_cpu(watchdog_task, hotcpu))