Darren Hart wrote:
> Subrata Modak wrote:
>>
>>
>> Hi,
>>> We have seen that prio_preempt testcase that is part of realtime
>>> tests occasionally hangs. This can be easily recreated on a 8-cpu
>>> system, but can be recreated on a 4-cpu system as well when run for
>>> a number of iterations.
>>>
>>> The problem occurs because the first worker thread sometimes fails
>>> to call cond_wait on the condvar through which the master thread
>>> signals it to start. Since the first thread needs to start the chain
>>> of signalling from then on, all other threads just sit in a
>>> cond_wait without ever being woken up.
>>>
>>> The fix is to have a barrier to ensure that the first worker thread
>>> doesn't miss the cond_signal.
>>>
>>> I have tested this patch by running 10s of thousands of iterations
>>> of the testcase. Without the patch I can recreate the problem fairly
>>> easily.
>>>
>>> Thanks,
>>> Sripathi.
>>>
>>> Signed-off-by: Sripathi Kodi <[EMAIL PROTECTED]>
>
> Acked-by: Darren Hart <[EMAIL PROTECTED]>
Thanks for the Ack. This has been merged.
Regards--
Subrata
>
>>>
>>
>> Over to the Real Time Linux Community for comments :-)
>>
>> Regards--
>> Subrata
>>> ---
>>> ltp-full-20080229/testcases/realtime/func/prio-preempt/prio-preempt.c.org
>>>
>>>
>>> 2008-03-12 22:10:05.000000000 +0530
>>> +++
>>> ltp-full-20080229/testcases/realtime/func/prio-preempt/prio-preempt.c
>>> 2008-03-12 22:14:02.000000000 +0530
>>> @@ -90,6 +90,8 @@ static int t_after_wait[NUM_WORKERS];
>>> static int ret = 0;
>>> static int run_jvmsim=0;
>>>
>>> +pthread_barrier_t barrier;
>>> +
>>> void usage(void)
>>> {
>>> rt_help();
>>> @@ -184,6 +186,8 @@ void *worker_thread(void* arg)
>>>
>>> /* block */
>>> rc = pthread_mutex_lock(&mutex[tid]);
>>> + if (tid == 0)
>>> + pthread_barrier_wait(&barrier);
>>> rc = pthread_cond_wait(&cond[tid], &mutex[tid]);
>>> rc = pthread_mutex_unlock(&mutex[tid]);
>>>
>>> @@ -234,6 +238,8 @@ void *master_thread(void* arg)
>>> {
>>> int i, pri_boost;
>>>
>>> + pthread_barrier_init(&barrier, NULL, 2);
>>> +
>>> /* start interrupter thread */
>>> if (int_threads) {
>>> pri_boost = 90;
>>> @@ -270,6 +276,9 @@ void *master_thread(void* arg)
>>> while (threads_running < NUM_WORKERS)
>>> usleep(100);
>>>
>>> + /* Ensure the first worker has called cond_wait */
>>> + pthread_barrier_wait(&barrier);
>>> +
>>> printf("Signaling first thread\n");
>>> pthread_mutex_lock(&mutex[0]);
>>> pthread_cond_signal(&cond[0]);
>>>
>>>
>>
>>
>
>
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