linux-kernel - [PATCH] sched/deadline: fix switching to -deadline

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Message-Id: <1492716656-5362-1-git-send-email-luca.abeni@santannapisa.it>
Date:   Thu, 20 Apr 2017 21:30:56 +0200
From:   luca abeni <luca.abeni@...tannapisa.it>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@....com>,
        Claudio Scordino <claudio@...dence.eu.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tommaso Cucinotta <tommaso.cucinotta@...up.it>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Luca Abeni <luca.abeni@...tannapisa.it>
Subject: [PATCH] sched/deadline: fix switching to -deadline

From: Luca Abeni <luca.abeni@...tannapisa.it>

When switching to -deadline, if the scheduling deadline of a task is
in the past then switched_to_dl() calls setup_new_entity() to properly
initialize the scheduling deadline and runtime.

The problem is that the task is enqueued _before_ having its parameters
initialized by setup_new_entity(), and this can cause problems.
For example, a task with its out-of-date deadline in the past will
potentially be enqueued as the highest priority one; however, its
adjusted deadline may not be the earliest one.

This patch fixes the problem by initializing the task's parameters before
enqueuing it.

Signed-off-by: Luca Abeni <luca.abeni@...tannapisa.it>
Reviewed-by: Daniel Bristot de Oliveira <bristot@...hat.com>
---
 kernel/sched/deadline.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index a2ce590..ec53d24 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -950,6 +950,10 @@ enqueue_dl_entity(struct sched_dl_entity *dl_se,
 		update_dl_entity(dl_se, pi_se);
 	else if (flags & ENQUEUE_REPLENISH)
 		replenish_dl_entity(dl_se, pi_se);
+	else if ((flags & ENQUEUE_RESTORE) &&
+		  dl_time_before(dl_se->deadline,
+				 rq_clock(rq_of_dl_rq(dl_rq_of_se(dl_se)))))
+		setup_new_dl_entity(dl_se);
 
 	__enqueue_dl_entity(dl_se);
 }
@@ -1767,14 +1771,6 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
 	if (!task_on_rq_queued(p))
 		return;
 
-	/*
-	 * If p is boosted we already updated its params in
-	 * rt_mutex_setprio()->enqueue_task(..., ENQUEUE_REPLENISH),
-	 * p's deadline being now already after rq_clock(rq).
-	 */
-	if (dl_time_before(p->dl.deadline, rq_clock(rq)))
-		setup_new_dl_entity(&p->dl);
-
 	if (rq->curr != p) {
 #ifdef CONFIG_SMP
 		if (p->nr_cpus_allowed > 1 && rq->dl.overloaded)
-- 
2.7.4