When a high priority process is acquiring a rtmutex which is held by a
low priority process, the latter's priority will be boosted up by calling
rt_mutex_setprio->__setscheduler_prio.
However, p->prio is changed but p->rt_priority is not, as a result, the
equation between prio and rt_priority is broken, which is:
prio = MAX_RT_PRIO - 1 - rt_priority
It's confusing to the user when it calls sched_getparam, which only
returns rt_priority.
This patch addresses this issue by adjusting rt_priority according to
the new value of prio, what's more, it also returns normal_prio for
CFS processes instead of just a zero.
Signed-off-by: Song Chen <[email protected]>
---
kernel/sched/core.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bb1ee6d7bdde..1c2c4ada08cc 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6933,14 +6933,16 @@ EXPORT_SYMBOL(default_wake_function);
static void __setscheduler_prio(struct task_struct *p, int prio)
{
+ p->prio = prio;
+
if (dl_prio(prio))
p->sched_class = &dl_sched_class;
- else if (rt_prio(prio))
+ else if (rt_prio(prio)) {
+ p->rt_priority = MAX_RT_PRIO - 1 - prio;
p->sched_class = &rt_sched_class;
+ }
else
p->sched_class = &fair_sched_class;
-
- p->prio = prio;
}
#ifdef CONFIG_RT_MUTEXES
@@ -8058,6 +8060,8 @@ SYSCALL_DEFINE2(sched_getparam, pid_t, pid, struct sched_param __user *, param)
if (task_has_rt_policy(p))
lp.sched_priority = p->rt_priority;
+ else
+ lp.sched_priority = normal_prio(p);
rcu_read_unlock();
/*
--
2.25.1
On Wed, 1 Feb 2023 18:01:20 +0800
Song Chen <[email protected]> wrote:
> When a high priority process is acquiring a rtmutex which is held by a
> low priority process, the latter's priority will be boosted up by calling
> rt_mutex_setprio->__setscheduler_prio.
>
> However, p->prio is changed but p->rt_priority is not, as a result, the
> equation between prio and rt_priority is broken, which is:
>
> prio = MAX_RT_PRIO - 1 - rt_priority
>
> It's confusing to the user when it calls sched_getparam, which only
> returns rt_priority.
If it is boosted, then that's an internal implementation and not the real
priority of the task. It should not be exposed to a user interface. In
fact, there's discussion of implementing a "proxy" algorithm which will
make what the "priority" of a task is even more complicated when acquiring
mutexes.
>
> This patch addresses this issue by adjusting rt_priority according to
> the new value of prio, what's more, it also returns normal_prio for
> CFS processes instead of just a zero.
The comment above sched_getparam() is:
/**
* sys_sched_getparam - get the RT priority of a thread
* @pid: the pid in question.
* @param: structure containing the RT priority.
*
* Return: On success, 0 and the RT priority is in @param. Otherwise, an error
* code.
*/
So returning the nice value is incorrect. If anything, perhaps it should
return -EINVAL if the task is not an RT task?
-- Steve
>
> Signed-off-by: Song Chen <[email protected]>
> ---