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SubjectRe: [BUG 2.6.25-rc3] scheduler/hotplug: some processes are dealocked when cpu is set to offline
On 03/04, Gautham R Shenoy wrote:
>
> So at times, the callback thread is blocked on kthread_stop(k) in
> softlockup.c, while other time, it was blocked in
> cleanup_workqueue_threads() in workqueue.c.

From another message:
>
> However, it remains in R< state

What about cwq->thread? Was it TASK_RUNNING too?

Perhaps, for some reason the task can't get CPU after migrating from
the now dead CPU.

I can't reproduce this problem on my one cpu P4-ht, perhaps you can
try something like the untested/uncompiled patch below?

Oleg.

--- include/linux/sched.h 2008-02-15 16:59:17.000000000 +0300
+++ include/linux/sched.h 2008-03-04 17:44:53.136738605 +0300
@@ -1121,6 +1121,7 @@ struct task_struct {
/* hung task detection */
unsigned long last_switch_timestamp;
unsigned long last_switch_count;
+ unsigned long xxx;
#endif
/* CPU-specific state of this task */
struct thread_struct thread;
--- kernel/fork.c 2008-02-15 16:59:17.000000000 +0300
+++ kernel/fork.c 2008-03-04 17:45:14.773033839 +0300
@@ -1097,6 +1097,7 @@ static struct task_struct *copy_process(
#ifdef CONFIG_DETECT_SOFTLOCKUP
p->last_switch_count = 0;
p->last_switch_timestamp = 0;
+ p->xxx = 0;
#endif

#ifdef CONFIG_TASK_XACCT
--- kernel/sched.c 2008-02-15 16:59:17.000000000 +0300
+++ kernel/sched.c 2008-03-04 17:48:42.308798646 +0300
@@ -1291,6 +1291,7 @@ static void enqueue_task(struct rq *rq,
sched_info_queued(p);
p->sched_class->enqueue_task(rq, p, wakeup);
p->se.on_rq = 1;
+ p->xxx = jiffies | 1;
}

static void dequeue_task(struct rq *rq, struct task_struct *p, int sleep)
@@ -3944,6 +3945,8 @@ need_resched_nonpreemptible:
preempt_enable_no_resched();
if (unlikely(test_thread_flag(TIF_NEED_RESCHED)))
goto need_resched;
+
+ current->xxx = 0;
}
EXPORT_SYMBOL(schedule);

--- kernel/softlockup.c 2008-02-15 16:59:17.000000000 +0300
+++ kernel/softlockup.c 2008-03-04 17:49:05.584414763 +0300
@@ -174,6 +174,27 @@ static void check_hung_task(struct task_
touch_nmi_watchdog();
}

+static void check_running_task(struct task_struct *t, unsigned long now)
+{
+ if (!sysctl_hung_task_timeout_secs)
+ return;
+
+ if (time_before(now, t->xxx + HZ * sysctl_hung_task_timeout_secs)
+ return;
+
+ printk(KERN_ERR "INFO: task %s:%d can't get CPU for more than "
+ "%ld seconds.\n", t->comm, t->pid,
+ sysctl_hung_task_timeout_secs);
+
+ if (!cpus_intersects(t->cpus_allowed, cpu_online_map))
+ printk(KERN_ERR "bad ->cpus_allowed\n");
+ if (!cpu_online(task_cpu(t)))
+ printk(KERN_ERR "bad ->cpu\n");
+
+ sched_show_task(t);
+ touch_nmi_watchdog();
+}
+
/*
* Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
* a really long time (120 seconds). If that happens, print out
@@ -183,6 +204,7 @@ static void check_hung_uninterruptible_t
{
int max_count = sysctl_hung_task_check_count;
unsigned long now = get_timestamp(this_cpu);
+ unsigned long jiff = jiffies;
struct task_struct *g, *t;

/*
@@ -192,15 +214,17 @@ static void check_hung_uninterruptible_t
if ((tainted & TAINT_DIE) || did_panic)
return;

- read_lock(&tasklist_lock);
+ rcu_read_lock();
do_each_thread(g, t) {
if (!--max_count)
goto unlock;
if (t->state & TASK_UNINTERRUPTIBLE)
check_hung_task(t, now);
+ if (!t->xxx)
+ check_running_task(t, jiff);
} while_each_thread(g, t);
unlock:
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
}

/*


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