linux-kernel - [PATCH] sched: Fix rt/dl hotplug condition

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Date:	Wed, 12 Feb 2014 10:49:30 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	kbuild@...org, Ingo Molnar <mingo@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] sched: Fix rt/dl hotplug condition

Dan Carpenter reported:

> kernel/sched/rt.c:1347 pick_next_task_rt() warn: variable dereferenced before check 'prev' (see line 1338)
> kernel/sched/deadline.c:1011 pick_next_task_dl() warn: variable dereferenced before check 'prev' (see line 1005)

Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Juri Lelli <juri.lelli@...il.com>
Fixes: 38033c37faab ("sched: Push down pre_schedule() and idle_balance()")
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
---
 kernel/sched/deadline.c | 2 +-
 kernel/sched/rt.c       | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index ed31ef66ab9d..d60008e4bce9 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1001,7 +1001,7 @@ struct task_struct *pick_next_task_dl(struct rq *rq, struct task_struct *prev)
 	dl_rq = &rq->dl;
 
 #ifdef CONFIG_SMP
-	if (dl_task(prev))
+	if (prev && dl_task(prev))
 		pull_dl_task(rq);
 #endif
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 72f9ec759972..7294b498b2c1 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1334,7 +1334,7 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev)
 
 #ifdef CONFIG_SMP
 	/* Try to pull RT tasks here if we lower this rq's prio */
-	if (rq->rt.highest_prio.curr > prev->prio)
+	if (prev && (rq->rt.highest_prio.curr > prev->prio))
 		pull_rt_task(rq);
 #endif
 
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