On Fri, Aug 16, 2019 at 06:06:26PM +0200, Sebastian Andrzej Siewior wrote: > If a task is PI-blocked (blocking on sleeping spinlock) then we don't want to > schedule a new kworker if we schedule out due to lock contention because !RT > does not do that as well.
s/as well/either/ > A spinning spinlock disables preemption and a worker > does not schedule out on lock contention (but spin). I'm not much liking this; it means that rt_mutex and mutex have different behaviour, and there are 'normal' rt_mutex users in the tree. > On RT the RW-semaphore implementation uses an rtmutex so > tsk_is_pi_blocked() will return true if a task blocks on it. In this case we > will now start a new worker I'm confused, by bailing out early it does _NOT_ start a new worker; or am I reading it wrong? > which may deadlock if one worker is waiting on > progress from another worker. > Since a RW-semaphore starts a new worker on !RT, we should do the same on RT. > > XFS is able to trigger this deadlock. > > Allow to schedule new worker if the current worker is PI-blocked. Which contradicts earlier parts of this changelog. > Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de> > --- > kernel/sched/core.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3945,7 +3945,7 @@ void __noreturn do_task_dead(void) > > static inline void sched_submit_work(struct task_struct *tsk) > { > - if (!tsk->state || tsk_is_pi_blocked(tsk)) > + if (!tsk->state) > return; > > /* > @@ -3961,6 +3961,9 @@ static inline void sched_submit_work(str > preempt_enable_no_resched(); > } > > + if (tsk_is_pi_blocked(tsk)) > + return; > + > /* > * If we are going to sleep and we have plugged IO queued, > * make sure to submit it to avoid deadlocks. What do we need that clause for? Why is pi_blocked special _at_all_?