On 09/06/11 19:53, Frank Rowand wrote:
> On 08/26/11 16:55, Paul E. McKenney wrote:
>> On Wed, Aug 24, 2011 at 04:58:49PM -0700, Frank Rowand wrote:
>>> On 08/13/11 03:53, Peter Zijlstra wrote:
>>>>
>>>> Whee, I can skip release announcements too!
>>>>
>>>> So no the subject ain't no mistake its not, 3.0.1-rt11 is there for the
>>>> grabs.
>
> < snip >
>
>>> I have a consistent (every boot) hang on boot. With a few
>>> hacks to get console output, I get the
>>>
>>> rcu_preempt_state detected stalls on CPUs/tasks
>
> < snip >
>
>>> This is an ARM NaviEngine (out of tree, so I also have applied
>>> a series of pages for platform support).
>>>
>>> CONFIG_PREEMPT_RT_FULL is set. Full config is attached.
>
> I have also replicated the problem on the ARM RealView (in tree) and
> without the RT patches.
>
>>
>> Hmmm... The last few that I have seen that looked like this were
>> due to my messing up rcutorture so that the RCU-boost testing kthreads
>> ran CPU-bound at real-time priority.
>>
>> Is it possible that something similar is happening on your system?
>>
>> Thanx, Paul
>
> The problem ended up being caused by the allowed cpus mask being set
> to all possible cpus for the ksoftirqd on the secondary processors.
> So the RCU softirq was never executing on cpu 2.
>
> I'll test the following patch on 3.1 tomorrow.
And the following patch is some clean up for code that is in the
RT patch. I do not know if this is needed, but after making the
changes in my first patch it seemed reasonable to add some extra
checks here, just in case softirq_check_pending_idle() gets
called in the window before the variable ksoftirqd gets set.
Signed-off-by: Frank Rowand <frank.rowand@xxxxxxxxxxx>
---
kernel/softirq.c | 25 14 + 11 - 0 !
1 file changed, 14 insertions(+), 11 deletions(-)
Index: b/kernel/softirq.c
===================================================================
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -87,18 +87,21 @@ void softirq_check_pending_idle(void)
struct task_struct *tsk;
tsk = __get_cpu_var(ksoftirqd);
- /*
- * The wakeup code in rtmutex.c wakes up the task
- * _before_ it sets pi_blocked_on to NULL under
- * tsk->pi_lock. So we need to check for both: state
- * and pi_blocked_on.
- */
- raw_spin_lock(&tsk->pi_lock);
+ if (tsk) {
+ /*
+ * The wakeup code in rtmutex.c wakes up the task
+ * _before_ it sets pi_blocked_on to NULL under
+ * tsk->pi_lock. So we need to check for both: state
+ * and pi_blocked_on.
+ */
+ raw_spin_lock(&tsk->pi_lock);
+
+ if (!tsk->pi_blocked_on &&
+ !(tsk->state == TASK_RUNNING))
+ warnpending = 1;
- if (!tsk->pi_blocked_on && !(tsk->state == TASK_RUNNING))
- warnpending = 1;
-
- raw_spin_unlock(&tsk->pi_lock);
+ raw_spin_unlock(&tsk->pi_lock);
+ }
}
if (warnpending) {
--
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