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>

1 files changed, 3 insertions, 3 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 79893123325c..db5c26692dd5 100644
--- 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;
 }