On Tue, 5 May 2015 18:08:01 +0200 (CEST)
Thomas Gleixner <t...@linutronix.de> wrote:
> Reported-by: Ronny Meeus <ronny.me...@gmail.com>
> Signed-off-by: Thomas Gleixner <t...@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;
--
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