sched: fix broken SCHED_RESET_ON_FORK handling

Setting child->prio = current->normal_prio _after_ SCHED_RESET_ON_FORK has
been handled for an RT parent gives birth to a deranged mutant child with
non-RT policy, but RT prio and sched_class.

Move PI leakage protection up, always set priorities and weight, and if the
child is leaving RT class, reset rt_priority to the proper value.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1311779695.8691.2.camel@marge.simson.net
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 12 insertions, 13 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index b1e8f0eca1f9..cf427bb2b65e 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2844,19 +2844,23 @@ void sched_fork(struct task_struct *p)
         p->state = TASK_RUNNING;
 
         /*
+         * Make sure we do not leak PI boosting priority to the child.
+         */
+        p->prio = current->normal_prio;
+
+        /*
          * Revert to default priority/policy on fork if requested.
          */
         if (unlikely(p->sched_reset_on_fork)) {
-                if (p->policy == SCHED_FIFO || p->policy == SCHED_RR) {
+                if (task_has_rt_policy(p)) {
                         p->policy = SCHED_NORMAL;
-                        p->normal_prio = p->static_prio;
-                }
-
-                if (PRIO_TO_NICE(p->static_prio) < 0) {
                         p->static_prio = NICE_TO_PRIO(0);
-                        p->normal_prio = p->static_prio;
-                        set_load_weight(p);
-                }
+                        p->rt_priority = 0;
+                } else if (PRIO_TO_NICE(p->static_prio) < 0)
+                        p->static_prio = NICE_TO_PRIO(0);
+
+                p->prio = p->normal_prio = __normal_prio(p);
+                set_load_weight(p);
 
                 /*
                  * We don't need the reset flag anymore after the fork. It has
@@ -2865,11 +2869,6 @@ void sched_fork(struct task_struct *p)
                 p->sched_reset_on_fork = 0;
         }
 
-        /*
-         * Make sure we do not leak PI boosting priority to the child.
-         */
-        p->prio = current->normal_prio;
-
         if (!rt_prio(p->prio))
                 p->sched_class = &fair_sched_class;