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sched/cpupri: skip isolated cpus

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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: Stephen Dickey <[email protected]>
This commit is contained in:
Stephen Dickey 2020-08-24 13:17:01 -07:00
commit db1f231281
1 changed files with 27 additions and 7 deletions
Download patch file Download diff file Expand all files Collapse all files

34
kernel/sched/cpupri.c
View file

@ -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 @@ retry:
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 @@ retry:
drop_nopreempts = false;
goto retry;
}
#endif
/*
* If we failed to find a fitting lowest_mask, kick off a new search