Re: Why can't I set the priority of softirq-hrt? (Re: 2.6.17-rt1)

[Esben Nielsen]

On Wed, 21 Jun 2006, Thomas Gleixner wrote:

> On Wed, 2006-06-21 at 16:43 +0100, Esben Nielsen wrote:
> > What about the patch below. It compiles and my UP labtop runs fine, but I
> > haven't otherwise tested it.  My labtop runs RTExec without hichups
> > until now.
>
> NAK, it puts the burden into the lock path and
What burden? An extra if (waiter.task) is the only thing!

> also does a remove / add
> which results in walking the chain twice.

The twice running through can be fixed.

> Find an version against the code in -mm below. Not too much tested yet.

What if setscheduler is called from interrup context as in the hrt timers?

Esben

> 	tglx
>
> Index: linux-2.6.17-rc6-mm/kernel/rtmutex.c
> ===================================================================
> --- linux-2.6.17-rc6-mm.orig/kernel/rtmutex.c	2006-06-21 13:34:34.000000000 +0200
> +++ linux-2.6.17-rc6-mm/kernel/rtmutex.c	2006-06-21 15:45:21.000000000 +0200
> @@ -160,7 +160,8 @@
> static int rt_mutex_adjust_prio_chain(task_t *task,
> 				      int deadlock_detect,
> 				      struct rt_mutex *orig_lock,
> -				      struct rt_mutex_waiter *orig_waiter)
> +				      struct rt_mutex_waiter *orig_waiter,
> +				      struct task_struct *top_task)
> {
> 	struct rt_mutex *lock;
> 	struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
> @@ -188,7 +189,7 @@
> 			prev_max = max_lock_depth;
> 			printk(KERN_WARNING "Maximum lock depth %d reached "
> 			       "task: %s (%d)\n", max_lock_depth,
> -			       current->comm, current->pid);
> +			       top_task->comm, top_task->pid);
> 		}
> 		put_task_struct(task);
>
> @@ -228,7 +229,7 @@
> 	}
>
> 	/* Deadlock detection */
> -	if (lock == orig_lock || rt_mutex_owner(lock) == current) {
> +	if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
> 		debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
> 		spin_unlock(&lock->wait_lock);
> 		ret = deadlock_detect ? -EDEADLK : 0;
> @@ -448,7 +449,8 @@
>
> 	spin_unlock(&lock->wait_lock);
>
> -	res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter);
> +	res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
> +					 current);
>
> 	spin_lock(&lock->wait_lock);
>
> @@ -561,12 +563,35 @@
>
> 	spin_unlock(&lock->wait_lock);
>
> -	rt_mutex_adjust_prio_chain(owner, 0, lock, NULL);
> +	rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current);
>
> 	spin_lock(&lock->wait_lock);
> }
>
> /*
> + * Recheck the pi chain, in case we got a priority setting
> + *
> + * Called from sched_setscheduler
> + */
> +void rt_mutex_adjust_pi(struct task_struct *task)
> +{
> +	struct rt_mutex_waiter *waiter = task->pi_blocked_on;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&task->pi_lock, flags);
> +
> +	if (!waiter || waiter->list_entry.prio == task->prio) {
> +		spin_unlock_irqrestore(&task->pi_lock, flags);
> +		return;
> +	}
> +
> +	get_task_struct(task);
> +	spin_unlock_irqrestore(&task->pi_lock, flags);
> +
> +	rt_mutex_adjust_prio_chain(task, 0, NULL, NULL, task);
> +}
> +
> +/*
>  * Slow path lock function:
>  */
> static int __sched
> @@ -633,6 +658,7 @@
> 			if (unlikely(ret))
> 				break;
> 		}
> +
> 		spin_unlock(&lock->wait_lock);
>
> 		debug_rt_mutex_print_deadlock(&waiter);
> Index: linux-2.6.17-rc6-mm/kernel/sched.c
> ===================================================================
> --- linux-2.6.17-rc6-mm.orig/kernel/sched.c	2006-06-21 13:34:34.000000000 +0200
> +++ linux-2.6.17-rc6-mm/kernel/sched.c	2006-06-21 18:21:16.000000000 +0200
> @@ -4028,8 +4028,7 @@
> int sched_setscheduler(struct task_struct *p, int policy,
> 		       struct sched_param *param)
> {
> -	int retval;
> -	int oldprio, oldpolicy = -1;
> +	int retval, oldprio, oldpolicy = -1;
> 	prio_array_t *array;
> 	unsigned long flags;
> 	runqueue_t *rq;
> @@ -4119,6 +4118,8 @@
> 	__task_rq_unlock(rq);
> 	spin_unlock_irqrestore(&p->pi_lock, flags);
>
> +	rt_mutex_adjust_pi(p);
> +
> 	return 0;
> }
> EXPORT_SYMBOL_GPL(sched_setscheduler);
> Index: linux-2.6.17-rc6-mm/include/linux/sched.h
> ===================================================================
> --- linux-2.6.17-rc6-mm.orig/include/linux/sched.h	2006-06-21 13:37:21.000000000 +0200
> +++ linux-2.6.17-rc6-mm/include/linux/sched.h	2006-06-21 15:43:23.000000000 +0200
> @@ -1123,11 +1123,13 @@
> #ifdef CONFIG_RT_MUTEXES
> extern int rt_mutex_getprio(task_t *p);
> extern void rt_mutex_setprio(task_t *p, int prio);
> +extern void rt_mutex_adjust_pi(task_t *p);
> #else
> static inline int rt_mutex_getprio(task_t *p)
> {
> 	return p->normal_prio;
> }
> +# define rt_mutex_adjust_pi(p)		do { } while (0)
> #endif
>
> extern void set_user_nice(task_t *p, long nice);
-
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