Fix RCU locking in sys_get_rt_task_param()

sys_get_rt_task_param() is rarely used and apparently attracted some
bitrot.

1 files changed, 10 insertions, 7 deletions

diff --git a/litmus/litmus.c b/litmus/litmus.c
index db5ce0e9c76e..885d75493118 100644
--- a/litmus/litmus.c
+++ b/litmus/litmus.c
@@ -184,21 +184,24 @@ asmlinkage long sys_get_rt_task_param(pid_t pid, struct rt_task __user * param)
         int retval = -EINVAL;
         struct task_struct *source;
         struct rt_task lp;
+
         if (param == 0 || pid < 0)
                 goto out;
-        read_lock(&tasklist_lock);
-        if (!(source = find_task_by_vpid(pid))) {
+
+        read_lock_irq(&tasklist_lock);
+        rcu_read_lock();
+        source = find_task_by_vpid(pid);
+        rcu_read_unlock();
+        if (!source) {
                 retval = -ESRCH;
-                goto out_unlock;
+                read_unlock_irq(&tasklist_lock);
+                goto out;
         }
         lp = source->rt_param.task_params;
-        read_unlock(&tasklist_lock);
+        read_unlock_irq(&tasklist_lock);
         /* Do copying outside the lock */
         retval =
             copy_to_user(param, &lp, sizeof(lp)) ? -EFAULT : 0;
-        return retval;
-      out_unlock:
-        read_unlock(&tasklist_lock);
       out:
         return retval;