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Commit db1f2312 authored by Stephen Dickey's avatar Stephen Dickey
Browse files

sched/cpupri: skip isolated cpus 



Currently there exists a path where cpupri_find could
return lowest_mask without removing isolated cpus. This
happened when __cpu_pri() didn't consider isolated
cpus and indicated that the lowest_mask was not empty.
Subsequently, cpupri_find_fitness() would find the
lowest_mask was empty, after removing isolated cpus.
This led to cpupri_find() being called again,
cpupri_find_fitness being re-entered, and this time,
since fitness_fn is NULL, returns true. This means there
is a case where lowest_mask only has isolated CPUs
and cpupri_find_fitness will indicate yes, cpus were found.

When invokved in the rt wakeup path through find_lowest_rq(),
this caused the pushes of rt tasks to be placed on
isolated cpus.  This also causes the the wakeups of rt
tasks on isolated cpus, although this is a rare occurrence.

Fix it by ensuring __cpu_pri() removes isolated cpus from
lowest_mask, which in turn causes cpupri_find_fitness() to
skip the current task_pri index prior to making any other
decision.  For the case where lowest_mask only has isolated
cpus left, this will result in no CPU being found, and
a return of false from cpupri_find_fitness().

Change-Id: I3e28b8366513ee51dc5c2d4eb0a2eb146c82f255
Signed-off-by: default avatarStephen Dickey <dickey@codeaurora.org>
parent 0afd6cbe

kernel/sched/cpupri.c

+27 −7
Original line number Diff line number Diff line
@@ -41,6 +41,7 @@ static int convert_prio(int prio) 
	return cpupri;

}



#ifdef CONFIG_SCHED_WALT

/**

 * drop_nopreempt_cpus - remove a cpu from the mask if it is likely

 *			 non-preemptible
@@ -61,9 +62,16 @@ drop_nopreempt_cpus(struct cpumask *lowest_mask) 
		cpu = cpumask_next(cpu, lowest_mask);

	}

}

#endif /* CONFIG_SCHED_WALT */



#ifndef CONFIG_SCHED_WALT

static inline int __cpupri_find(struct cpupri *cp, struct task_struct *p,

				struct cpumask *lowest_mask, int idx)

#else

static inline int __cpupri_find(struct cpupri *cp, struct task_struct *p,

				struct cpumask *lowest_mask, int idx,

				bool drop_nopreempts)

#endif

{

	struct cpupri_vec *vec  = &cp->pri_to_cpu[idx];

	int skip = 0;
@@ -100,6 +108,13 @@ static inline int __cpupri_find(struct cpupri *cp, struct task_struct *p, 
	if (lowest_mask) {

		cpumask_and(lowest_mask, p->cpus_ptr, vec->mask);



#ifdef CONFIG_SCHED_WALT

		if (drop_nopreempts)

			drop_nopreempt_cpus(lowest_mask);



		cpumask_andnot(lowest_mask, lowest_mask,

			       cpu_isolated_mask);

#endif

		/*

		 * We have to ensure that we have at least one bit

		 * still set in the array, since the map could have
@@ -144,26 +159,28 @@ int cpupri_find_fitness(struct cpupri *cp, struct task_struct *p, 
{

	int task_pri = convert_prio(p->prio);

	int idx, cpu;



#ifdef CONFIG_SCHED_WALT

	bool drop_nopreempts = task_pri <= MAX_RT_PRIO;

#endif



	BUG_ON(task_pri >= CPUPRI_NR_PRIORITIES);



#ifdef CONFIG_SCHED_WALT

retry:

#endif

	for (idx = 0; idx < task_pri; idx++) {



#ifndef CONFIG_SCHED_WALT

		if (!__cpupri_find(cp, p, lowest_mask, idx))

#else

		if (!__cpupri_find(cp, p, lowest_mask, idx, drop_nopreempts))

			continue;

#endif



		if (!lowest_mask || !fitness_fn)

			return 1;



#ifdef CONFIG_SCHED_WALT

		cpumask_andnot(lowest_mask, lowest_mask,

			       cpu_isolated_mask);

#endif

		if (drop_nopreempts)

			drop_nopreempt_cpus(lowest_mask);



		/* Ensure the capacity of the CPUs fit the task */

		for_each_cpu(cpu, lowest_mask) {

			if (!fitness_fn(p, cpu))
@@ -179,6 +196,8 @@ int cpupri_find_fitness(struct cpupri *cp, struct task_struct *p, 


		return 1;

	}



#ifdef CONFIG_SCHED_WALT

	/*

	 * If we can't find any non-preemptible cpu's, retry so we can

	 * find the lowest priority target and avoid priority inversion.
@@ -187,6 +206,7 @@ int cpupri_find_fitness(struct cpupri *cp, struct task_struct *p, 
		drop_nopreempts = false;

		goto retry;

	}

#endif



	/*

	 * If we failed to find a fitting lowest_mask, kick off a new search