sched: Use rcu in sched_get_rr_param()

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@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20091209100706.862897167@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/sched.c b/kernel/sched.c
index 7989312..db5c266 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6873,7 +6873,7 @@ SYSCALL_DEFINE2(sched_rr_get_interval, pid_t, pid,
                return -EINVAL;
 
        retval = -ESRCH;
-       read_lock(&tasklist_lock);
+       rcu_read_lock();
        p = find_process_by_pid(pid);
        if (!p)
                goto out_unlock;
@@ -6886,13 +6886,13 @@ SYSCALL_DEFINE2(sched_rr_get_interval, pid_t, pid,
        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;
 }