Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fixes from Ingo Molnar:

 - Apply a number of membarrier related fixes and cleanups, which fixes
   a use-after-free race in the membarrier code

 - Introduce proper RCU protection for tasks on the runqueue - to get
   rid of the subtle task_rcu_dereference() interface that was easy to
   get wrong

 - Misc fixes, but also an EAS speedup

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/fair: Avoid redundant EAS calculation
  sched/core: Remove double update_max_interval() call on CPU startup
  sched/core: Fix preempt_schedule() interrupt return comment
  sched/fair: Fix -Wunused-but-set-variable warnings
  sched/core: Fix migration to invalid CPU in __set_cpus_allowed_ptr()
  sched/membarrier: Return -ENOMEM to userspace on memory allocation failure
  sched/membarrier: Skip IPIs when mm->mm_users == 1
  selftests, sched/membarrier: Add multi-threaded test
  sched/membarrier: Fix p->mm->membarrier_state racy load
  sched/membarrier: Call sync_core only before usermode for same mm
  sched/membarrier: Remove redundant check
  sched/membarrier: Fix private expedited registration check
  tasks, sched/core: RCUify the assignment of rq->curr
  tasks, sched/core: With a grace period after finish_task_switch(), remove unnecessary code
  tasks, sched/core: Ensure tasks are available for a grace period after leaving the runqueue
  tasks: Add a count of task RCU users
  sched/core: Convert vcpu_is_preempted() from macro to an inline function
  sched/fair: Remove unused cfs_rq_clock_task() function

1 files changed, 5 insertions, 3 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 60763c043aa3..f9572f416126 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -915,10 +915,12 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
                 tsk->cpus_ptr = &tsk->cpus_mask;
 
         /*
-         * One for us, one for whoever does the "release_task()" (usually
-         * parent)
+         * One for the user space visible state that goes away when reaped.
+         * One for the scheduler.
          */
-        refcount_set(&tsk->usage, 2);
+        refcount_set(&tsk->rcu_users, 2);
+        /* One for the rcu users */
+        refcount_set(&tsk->usage, 1);
 #ifdef CONFIG_BLK_DEV_IO_TRACE
         tsk->btrace_seq = 0;
 #endif