Re: [LTP] [PATCH] prio-wake: avoid glibc to kernel sleep race

[Darren Hart <dvhltc@us.ibm.com>]

This patch does not appear in current CVS. Please apply.

Thanks,

Darren Hart

Darren Hart wrote:
> prio-wake: avoid glibc to kernel sleep race
> 
> In the unlocked broadcast scenario, there exists a race between when the
> running_threads variable reaches rt_threads and when the last worker_thread
> blocks in the kernel after a cond_wait(). It is possible for a thread to miss
> the broadcast if it fails to sleep before the broadcast is issued.  
> 
> The previous code did not guarantee a small window of time to allow the threads
> to get to sleep.  It also used an unreasonably large sleep time which
> unnecessarily extended the length of the test run time.  This patch ensures some
> time is given to the threads to get to sleep and at the same time uses a much
> shorter (1000x) sleep period which results in a 50-100x reduction in test run
> time. Lastly, two unecessary loops waiting for the threads to complete were
> removed, relying on pthread_join() instead to wait for the threads to complete.
> 
> Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
> Acked-by: Will Schmidt <will_schmidt@vnet.ibm.com>
> 
> ---
>  func/prio-wake/prio-wake.c |   10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> Index: realtime/func/prio-wake/prio-wake.c
> ===================================================================
> --- realtime.orig/func/prio-wake/prio-wake.c
> +++ realtime/func/prio-wake/prio-wake.c
> @@ -108,7 +108,10 @@ void *master_thread(void* arg)
> 
>  	/* make sure children are started */
>  	while (running_threads < rt_threads)
> -		sleep(1);
> +		usleep(1000);
> +	/* give the worker threads a chance to get to sleep in the kernel
> +	 * in the unlocked broadcast case. */
> +	usleep(1000);
> 
>  	start = rt_gettime() - beginrun;
> 
> @@ -120,8 +123,6 @@ void *master_thread(void* arg)
>  	if (locked_broadcast)
>  		rc = pthread_mutex_unlock(&mutex);
> 
> -	while (running_threads > 0)
> -		sleep(1);
>  	return NULL;
>  }
> 
> @@ -157,9 +158,6 @@ void *worker_thread(void* arg)
> 
>  	rc = pthread_mutex_unlock(&mutex);
> 
> -	/* wait for all threads to quit */
> -	while (running_threads > 0)
> -		sleep(1);
>  	return NULL;
>  }
> 


-- 
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team

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