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]>
>
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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