On Wed, Oct 01, 2014 at 01:04:22AM +0400, Kirill Tkhai wrote: > From: Kirill Tkhai <ktk...@parallels.com> > > hrtimer_try_to_cancel() may bring a suprise, its call may fail.
Well, not really a surprise that, its a _try_ operation after all. > raw_spin_lock(&rq->lock) > ... dl_task_timer > raw_spin_lock(&rq->lock) > ... raw_spin_lock(&rq->lock) ... > switched_from_dl() ... ... > hrtimer_try_to_cancel() ... ... > switched_to_fair() ... ... > ... ... ... > ... ... ... > raw_spin_unlock(&rq->lock) ... (asquired) > ... ... ... > ... ... ... > do_exit() ... ... > schedule() ... ... > raw_spin_lock(&rq->lock) ... > raw_spin_unlock(&rq->lock) > ... ... ... > raw_spin_unlock(&rq->lock) ... > raw_spin_lock(&rq->lock) > ... ... (asquired) > put_task_struct() ... ... > free_task_struct() ... ... > ... ... > raw_spin_unlock(&rq->lock) > ... (asquired) ... > ... ... ... > ... Surprise!!! ... > > So, let's implement 100% guaranteed way to cancel the timer and let's > be sure we are safe even in very unlikely situations. > > We do not create any problem with rq unlocking, because it already > may happed below in pull_dl_task(). No problem with deadline tasks > balancing too. That doesn't sound right. pull_dl_task() is an entirely different callchain than switched_from(). Now it might still be fine, but you cannot compare it with pull_dl_task. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
