[patch 4/4] sched: Use rcu in sched_get_rr_param

[Thomas Gleixner]

read_lock(&tasklist_lock) does not protect sys_sched_get_rr_param()
against a concurrent update of the policy or scheduler parameters as
do_sched_scheduler() does not take the tasklist_lock.

The access to task->sched_class->get_rr_interval is protected by
task_rq_lock(task).

Use rcu_read_lock() to protect find_task_by_vpid() and prevent the
task struct from going away.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 kernel/sched.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Index: linux-2.6-tip/kernel/sched.c
===================================================================
--- linux-2.6-tip.orig/kernel/sched.c
+++ linux-2.6-tip/kernel/sched.c
@@ -6892,7 +6892,7 @@ SYSCALL_DEFINE2(sched_rr_get_interval, p
 		return -EINVAL;
 
 	retval = -ESRCH;
-	read_lock(&tasklist_lock);
+	rcu_read_lock();
 	p = find_process_by_pid(pid);
 	if (!p)
 		goto out_unlock;
@@ -6905,13 +6905,13 @@ SYSCALL_DEFINE2(sched_rr_get_interval, p
 	time_slice = p->sched_class->get_rr_interval(rq, p);
 	task_rq_unlock(rq, &flags);
 
-	read_unlock(&tasklist_lock);
+	rcu_read_unlock();
 	jiffies_to_timespec(time_slice, &t);
 	retval = copy_to_user(interval, &t, sizeof(t)) ? -EFAULT : 0;
 	return retval;
 
 out_unlock:
-	read_unlock(&tasklist_lock);
+	rcu_read_unlock();
 	return retval;
 }
 


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