[patch 2/2] sched: Protect sched_rr_get_param access to task->sched_class

[Thomas Gleixner <tglx@linutronix.de>]

[-- Attachment #1: sched-fix-sched-get-rr-param-race.patch --]
[-- Type: text/plain, Size: 988 bytes --]

sched_rr_get_param calls task->sched_class->get_rr_interval(task)
without protection against a concurrent sched_setscheduler() call
which modifies task->sched_class.

Serialize the access with task_rq_lock(task);

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/sched.c |    4 ++++
 1 file changed, 4 insertions(+)

Index: linux-2.6-tip/kernel/sched.c
===================================================================
--- linux-2.6-tip.orig/kernel/sched.c
+++ linux-2.6-tip/kernel/sched.c
@@ -6887,6 +6887,8 @@ SYSCALL_DEFINE2(sched_rr_get_interval, p
 {
 	struct task_struct *p;
 	unsigned int time_slice;
+	unsigned long flags;
+	struct rq *rq;
 	int retval;
 	struct timespec t;
 
@@ -6903,7 +6905,9 @@ SYSCALL_DEFINE2(sched_rr_get_interval, p
 	if (retval)
 		goto out_unlock;
 
+	rq = task_rq_lock(p, &flags);
 	time_slice = p->sched_class->get_rr_interval(p);
+	task_rq_unlock(rq, &flags);
 
 	read_unlock(&tasklist_lock);
 	jiffies_to_timespec(time_slice, &t);