[PATCH 1/3] sched/deadline: clear dl_entity params when setscheduling to different class

[Juri Lelli]

When a task is using SCHED_DEADLINE and the user setschedules it to a different
class its sched_dl_entity static parameters are not cleaned up. This causes a
bug if the user sets it back to SCHED_DEADLINE with the same parameters again.
The problem resides in the check we perform at the very beginning of
dl_overflow():

	if (new_bw == p->dl.dl_bw)
		return 0;

This condition is met in the case depicted above, so the function returns and
dl_b->total_bw is not updated (the p->dl.dl_bw is not added to it). After this,
admission control is broken.

This patch fixes the thing, properly clearing static parameters for a task
that ceases to use SCHED_DEADLINE.

Reported-by: Daniele Alessandrelli <daniele.alessandrelli@xxxxxxxxx>
Reported-by: Daniel Wagner <daniel.wagner@xxxxxxxxxxxx>
Reported-by: Vincent Legout <vincent@xxxxxxxxxxx>
Tested-by: Luca Abeni <luca.abeni@xxxxxxxx>
Signed-off-by: Juri Lelli <juri.lelli@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxx>
Cc: Dario Faggioli <raistlin@xxxxxxxx>
Cc: Michael Trimarchi <michael@xxxxxxxxxxxxxxxxxxxx>
Cc: Fabio Checconi <fchecconi@xxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 kernel/sched/core.c     | 19 +++++++++++++++----
 kernel/sched/deadline.c |  2 ++
 kernel/sched/sched.h    |  3 +++
 3 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ec1a286..581a429 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1776,6 +1776,20 @@ int wake_up_state(struct task_struct *p, unsigned int state)
 }
 
 /*
+ * This function clears the sched_dl_entity static params.
+ */
+void __dl_clear_params(struct task_struct *p)
+{
+	struct sched_dl_entity *dl_se = &p->dl;
+
+	dl_se->dl_runtime = 0;
+	dl_se->dl_deadline = 0;
+	dl_se->dl_period = 0;
+	dl_se->flags = 0;
+	dl_se->dl_bw = 0;
+}
+
+/*
  * Perform scheduler related setup for a newly forked process p.
  * p is forked by current.
  *
@@ -1799,10 +1813,7 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
 
 	RB_CLEAR_NODE(&p->dl.rb_node);
 	hrtimer_init(&p->dl.dl_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
-	p->dl.dl_runtime = p->dl.runtime = 0;
-	p->dl.dl_deadline = p->dl.deadline = 0;
-	p->dl.dl_period = 0;
-	p->dl.flags = 0;
+	__dl_clear_params(p);
 
 	INIT_LIST_HEAD(&p->rt.run_list);
 
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 255ce13..4a51b14 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1569,6 +1569,8 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
 	if (hrtimer_active(&p->dl.dl_timer) && !dl_policy(p->policy))
 		hrtimer_try_to_cancel(&p->dl.dl_timer);
 
+	__dl_clear_params(p);
+
 #ifdef CONFIG_SMP
 	/*
 	 * Since this might be the only -deadline task on the rq,
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 579712f..4890484 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -126,6 +126,9 @@ struct rt_bandwidth {
 	u64			rt_runtime;
 	struct hrtimer		rt_period_timer;
 };
+
+void __dl_clear_params(struct task_struct *p);
+
 /*
  * To keep the bandwidth of -deadline tasks and groups under control
  * we need some place where:
-- 
2.1.0


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