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

Rishikesh K Rajak
2010-04-22T06:09:27Z

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
>
> ------------------------------------------------------------------------------
> _______________________________________________
> Ltp-list mailing list
> Ltp-list@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/ltp-list

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