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Subject[144/145] sched: Dont use possibly stale sched_class
2.6.32-stable review patch.  If anyone has any objections, please let me know.

----------------
From: Thomas Gleixner <tglx@linutronix.de>

commit 83ab0aa0d5623d823444db82c3b3c34d7ec364ae upstream.

setscheduler() saves task->sched_class outside of the rq->lock held
region for a check after the setscheduler changes have become
effective. That might result in checking a stale value.

rtmutex_setprio() has the same problem, though it is protected by
p->pi_lock against setscheduler(), but for correctness sake (and to
avoid bad examples) it needs to be fixed as well.

Retrieve task->sched_class inside of the rq->lock held region.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
kernel/sched.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6009,7 +6009,7 @@ void rt_mutex_setprio(struct task_struct
unsigned long flags;
int oldprio, on_rq, running;
struct rq *rq;
- const struct sched_class *prev_class = p->sched_class;
+ const struct sched_class *prev_class;

BUG_ON(prio < 0 || prio > MAX_PRIO);

@@ -6017,6 +6017,7 @@ void rt_mutex_setprio(struct task_struct
update_rq_clock(rq);

oldprio = p->prio;
+ prev_class = p->sched_class;
on_rq = p->se.on_rq;
running = task_current(rq, p);
if (on_rq)
@@ -6244,7 +6245,7 @@ static int __sched_setscheduler(struct t
{
int retval, oldprio, oldpolicy = -1, on_rq, running;
unsigned long flags;
- const struct sched_class *prev_class = p->sched_class;
+ const struct sched_class *prev_class;
struct rq *rq;
int reset_on_fork;

@@ -6358,6 +6359,7 @@ recheck:
p->sched_reset_on_fork = reset_on_fork;

oldprio = p->prio;
+ prev_class = p->sched_class;
__setscheduler(rq, p, policy, param->sched_priority);

if (running)



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