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

[Esben Nielsen <nielsen.esben@googlemail.com>]

On Wed, 21 Jun 2006, Esben Nielsen wrote:

> On Wed, 21 Jun 2006, Steven Rostedt wrote:
>
> >  On Tue, 20 Jun 2006, Esben Nielsen wrote:
> >
> > > 
> > > >  I have to check, whether the priority is propagated when the softirq 
> > > >  is
> > > >  blocked on a lock. If not its a bug and has to be fixed.
> > > 
> > >  I think the simplest solution would be to add
> > > 
> > >           if (p->blocked_on)
> > >                   wake_up_process(p);
> > > 
> > >  in __setscheduler().
> > > 
> >
> >  Except that wake_up_process calls try_to_wakeup which grabs the runqueue
> >  lock, which unfortunately is already held when __setscheduler is called.
>
> Yeah, I saw. Move it out in setscheduler() then. I'll try to fix it, but I am 
> not sure I can make a test if it works.

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.

Esben

Index: linux-2.6.17-rt1/kernel/rtmutex.c
===================================================================
--- linux-2.6.17-rt1.orig/kernel/rtmutex.c
+++ linux-2.6.17-rt1/kernel/rtmutex.c
@@ -625,6 +625,7 @@ rt_lock_slowlock(struct rt_mutex *lock _

 	debug_rt_mutex_init_waiter(&waiter);
 	waiter.task = NULL;
+	waiter.save_state = 1;

 	spin_lock(&lock->wait_lock);

@@ -687,6 +688,19 @@ rt_lock_slowlock(struct rt_mutex *lock _
 		state = xchg(&current->state, TASK_UNINTERRUPTIBLE);
 		if (unlikely(state == TASK_RUNNING))
 			saved_state = TASK_RUNNING;
+
+		if (unlikely(waiter.task) &&
+		    waiter.list_entry.prio != current->prio) {
+			/*
+			 * We still not have the lock, but we are woken up with
+			 * a different prio than the one we waited with
+			 * originally. We remove the wait entry now and then
+			 * reinsert ourselves with the right priority
+			 */
+			remove_waiter(lock, &waiter __IP__);
+			waiter.task = NULL;
+		}
+
 	}

 	state = xchg(&current->state, saved_state);
@@ -798,6 +812,7 @@ rt_mutex_slowlock(struct rt_mutex *lock,

 	debug_rt_mutex_init_waiter(&waiter);
 	waiter.task = NULL;
+	waiter.save_state = 0;

 	spin_lock(&lock->wait_lock);

@@ -877,6 +892,18 @@ rt_mutex_slowlock(struct rt_mutex *lock,

 		current->flags |= saved_flags;
 		set_current_state(state);
+
+		if (unlikely(waiter.task) &&
+		    waiter.list_entry.prio != current->prio) {
+			/*
+			 * We still not have the lock, but we are woken up with
+			 * a different prio than the one we waited with
+			 * originally. We remove the wait entry now and then
+			 * reinsert ourselves with the right priority
+			 */
+			remove_waiter(lock, &waiter __IP__);
+			waiter.task = NULL;
+		}
 	}

 	set_current_state(TASK_RUNNING);
Index: linux-2.6.17-rt1/kernel/sched.c
===================================================================
--- linux-2.6.17-rt1.orig/kernel/sched.c
+++ linux-2.6.17-rt1/kernel/sched.c
@@ -57,6 +57,8 @@

 #include <asm/unistd.h>

+#include "rtmutex_common.h"
+
 /*
  * Convert user-nice values [ -20 ... 0 ... 19 ]
  * to static priority [ MAX_RT_PRIO..MAX_PRIO-1 ],
@@ -646,7 +648,9 @@ static inline void sched_info_switch(tas
 #define sched_info_switch(t, next)	do { } while (0)
 #endif /* CONFIG_SCHEDSTATS */

+#ifdef CONFIG_SMP
 static __cacheline_aligned_in_smp atomic_t rt_overload;
+#endif

 static inline void inc_rt_tasks(task_t *p, runqueue_t *rq)
 {
@@ -1473,10 +1477,11 @@ static inline int wake_idle(int cpu, tas
 static int try_to_wake_up(task_t *p, unsigned int state, int sync, int mutex)
 {
 	int cpu, this_cpu, success = 0;
-	runqueue_t *this_rq, *rq;
+	runqueue_t *rq;
 	unsigned long flags;
 	long old_state;
 #ifdef CONFIG_SMP
+	runqueue_t *this_rq;
 	unsigned long load, this_load;
 	struct sched_domain *sd, *this_sd = NULL;
 	int new_cpu;
@@ -4351,6 +4356,18 @@ int setscheduler(struct task_struct *p,
 			resched_task(rq->curr);
 	}
 	task_rq_unlock(rq, &flags);
+
+	/*
+	 * If the process is blocked on rt-mutex, it will now wake up and
+	 * reinsert itself into the wait list and boost the owner correctly
+	 */
+	if (p->pi_blocked_on) {
+		if (p->pi_blocked_on->save_state)
+			wake_up_process_mutex(p);
+		else
+			wake_up_process(p);
+	}
+
 	spin_unlock_irqrestore(&p->pi_lock, fp);
 	return 0;
 }
@@ -7086,4 +7103,3 @@ void notrace preempt_enable_no_resched(v

 EXPORT_SYMBOL(preempt_enable_no_resched);
 #endif
-
Index: linux-2.6.17-rt1/kernel/rtmutex_common.h
===================================================================
--- linux-2.6.17-rt1.orig/kernel/rtmutex_common.h
+++ linux-2.6.17-rt1/kernel/rtmutex_common.h
@@ -49,6 +49,7 @@ struct rt_mutex_waiter {
 	struct plist_node	pi_list_entry;
 	struct task_struct	*task;
 	struct rt_mutex		*lock;
+	int                     save_state;
 #ifdef CONFIG_DEBUG_RT_MUTEXES
 	unsigned long		ip;
 	pid_t			deadlock_task_pid;
-
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