linux-kernel - [PATCH 6/8] sched/deadline: Don't return meaningless cpu in cpudl_maximum

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Date:   Thu, 23 Mar 2017 19:32:41 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     <peterz@...radead.org>, <mingo@...nel.org>
CC:     <linux-kernel@...r.kernel.org>, <juri.lelli@...il.com>,
        <rostedt@...dmis.org>, <kernel-team@....com>
Subject: [PATCH 6/8] sched/deadline: Don't return meaningless cpu in cpudl_maximum_cpu()

When the heap tree is empty, cp->elements[0].cpu has meaningless value.
We need to consider the case.

Signed-off-by: Byungchul Park <byungchul.park@....com>
---
 kernel/sched/cpudeadline.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index 37bbb66..21404b8 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -107,7 +107,8 @@ static void cpudl_heapify(struct cpudl_item *e, int size, int idx)
 
 static inline int cpudl_maximum_cpu(struct cpudl *cp)
 {
-	return cp->elements[0].cpu;
+	int cpu = cp->elements[0].cpu;
+	return cp->elements[cpu].idx == IDX_INVALID ? -1 : cpu;
 }
 
 static inline u64 cpudl_maximum_dl(struct cpudl *cp)
@@ -127,7 +128,8 @@ static int cpudl_fast_find(struct cpudl *cp, struct task_struct *p)
 	max_dl = cpudl_maximum_dl(cp);
 	raw_spin_unlock_irqrestore(&cp->lock, flags);
 
-	if (cpumask_test_cpu(max_cpu, &p->cpus_allowed) &&
+	if (max_cpu != -1 &&
+	    cpumask_test_cpu(max_cpu, &p->cpus_allowed) &&
 	    dl_time_before(dl_se->deadline, max_dl))
 		return max_cpu;
 
-- 
1.9.1