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

[Rishikesh K Rajak <risrajak@linux.vnet.ibm.com>]

On Wed, Apr 21, 2010 at 01:23:18PM -0700, Darren Hart wrote:
> This patch does not appear in current CVS. Please apply.
Hi darren,

Committed
5162b710bfc574107d915093c08b198f0a15727e

Thanks.

-Rishi
> 
> 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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-- 
Thanks & Regards
Rishi
LTP Maintainer
IBM, LTC, Bangalore
Please join IRC #ltp @ irc.freenode.net

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