[PATCH] sched: Fixup scheduler syscall LTP fails

[Peter Zijlstra]

Subject: sched: Fixup scheduler syscall LTP fails

Wu reported:

> ltp.sched_setparam02.1.TFAIL
> ltp.sched_setparam02.2.TFAIL
> ltp.sched_setparam02.3.TFAIL
> ltp.sched_setparam03.1.TFAIL

There were 2 things wrong; firstly __setscheduler() failed on
sched_setparam()'s policy = -1, fix that by reading from p->policy in
that case.

Secondly, getparam() (and getattr()) would still report !0
sched_priority for !FIFO/RR tasks after having been such. So
unconditionally set p->rt_priority.

Fixes: d50dde5a10f3 ("sched: Add new scheduler syscalls to support an extended scheduling parameters ABI")
Reported-by: Fengguang Wu <fengguang.wu@xxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
 kernel/sched/core.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0326c06953eb..50e99f2cf98b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3183,15 +3183,23 @@ static void __setscheduler(struct rq *rq, struct task_struct *p,
 {
 	int policy = attr->sched_policy;
 
+	if (policy == -1) /* setparam */
+		policy = p->policy;
+
 	p->policy = policy;
 
 	if (dl_policy(policy))
 		__setparam_dl(p, attr);
-	else if (rt_policy(policy))
-		p->rt_priority = attr->sched_priority;
-	else
+	else if (fair_policy(policy))
 		p->static_prio = NICE_TO_PRIO(attr->sched_nice);
 
+	/*
+	 * __sched_setscheduler() ensures attr->sched_priority == 0 when
+	 * !rt_policy. Always setting this ensures that things like
+	 * getparam()/getattr() don't report silly values for !rt tasks.
+	 */
+	p->rt_priority = attr->sched_priority;
+
 	p->normal_prio = normal_prio(p);
 	p->prio = rt_mutex_getprio(p);
 
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