Messages in this thread | | | Date | Tue, 5 May 2015 12:29:20 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH] sched: Handle priority boosted tasks proper in setscheduler() |
| |
On Tue, 5 May 2015 18:08:01 +0200 (CEST) Thomas Gleixner <tglx@linutronix.de> wrote:
> Reported-by: Ronny Meeus <ronny.meeus@gmail.com> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > --- > kernel/locking/rtmutex.c | 10 ++++++---- > kernel/sched/core.c | 11 +++++------ > 2 files changed, 11 insertions(+), 10 deletions(-) > > Index: tip/kernel/locking/rtmutex.c > =================================================================== > --- tip.orig/kernel/locking/rtmutex.c > +++ tip/kernel/locking/rtmutex.c > @@ -265,15 +265,17 @@ struct task_struct *rt_mutex_get_top_tas > } > > /* > - * Called by sched_setscheduler() to check whether the priority change > - * is overruled by a possible priority boosting. > + * Called by sched_setscheduler() to get the priority which will be > + * effective after the change. > */ > int rt_mutex_check_prio(struct task_struct *task, int newprio) > { > if (!task_has_pi_waiters(task)) > - return 0; > + return newprio; > > - return task_top_pi_waiter(task)->task->prio <= newprio; > + if (task_top_pi_waiter(task)->task->prio <= newprio) > + return task_top_pi_waiter(task)->task->prio; > + return newprio; > } > > /* > Index: tip/kernel/sched/core.c > =================================================================== > --- tip.orig/kernel/sched/core.c > +++ tip/kernel/sched/core.c > @@ -3414,7 +3414,7 @@ static int __sched_setscheduler(struct t > int newprio = dl_policy(attr->sched_policy) ? MAX_DL_PRIO - 1 : > MAX_RT_PRIO - 1 - attr->sched_priority; > int retval, oldprio, oldpolicy = -1, queued, running; > - int policy = attr->sched_policy; > + int new_effective_prio, policy = attr->sched_policy; > unsigned long flags; > const struct sched_class *prev_class; > struct rq *rq; > @@ -3596,15 +3596,14 @@ change: > oldprio = p->prio; > > /* > - * Special case for priority boosted tasks. > - * > - * If the new priority is lower or equal (user space view) > - * than the current (boosted) priority, we just store the new > + * Take priority boosted tasks into account. If the new > + * effective priority is unchanged, we just store the new > * normal parameters and do not touch the scheduler class and > * the runqueue. This will be done when the task deboost > * itself. > */ > - if (rt_mutex_check_prio(p, newprio)) { > + new_effective_prio = rt_mutex_check_prio(p, newprio); > + if (new_effective_prio == oldprio) {
When I first heard of this problem, I started writing code to fix this and came up with pretty much the exact same answer.
I got pulled onto other things so I never finished it, but one thing that worried me about this fix is this:
T1 - FIFO policy (prio = 10) lock(rtmutex);
T2 (prio = 20) lock(rtmutex) boost T1 (prio = 20)
TI (prio = 20) sys_sched_setscheduler(prio = 30) TI (prio = 30)
T1 (prio = 30) sys_sched_setscheduler(SCHED_OTHER) new_effective_prio = 20, oldprio = 30
Before the code stopped at the rt_mutex_check_prio(), but now it continues. Will having the policy change cause problems here?
-- Steve
> __setscheduler_params(p, attr); > task_rq_unlock(rq, p, &flags); > return 0;
| |