2 files changed, 8 insertions, 17 deletions

diff --git a/litmus/litmus.c b/litmus/litmus.c
index 73af6c3010d6..301390148d02 100644
--- a/litmus/litmus.c
+++ b/litmus/litmus.c
@@ -529,6 +529,8 @@ static int __init _init_litmus(void)
          */
         printk("Starting LITMUS^RT kernel\n");
 
+        BUILD_BUG_ON(sizeof(union np_flag) != sizeof(uint32_t));
+
         register_sched_plugin(&linux_sched_plugin);
 
         bheap_node_cache    = KMEM_CACHE(bheap_node, SLAB_PANIC);
diff --git a/litmus/sched_plugin.c b/litmus/sched_plugin.c
index d54886df1f57..00a1900d6457 100644
--- a/litmus/sched_plugin.c
+++ b/litmus/sched_plugin.c
@@ -35,29 +35,18 @@ void preempt_if_preemptable(struct task_struct* t, int cpu)
                         /* local CPU case */
                         /* check if we need to poke userspace */
                         if (is_user_np(t))
-                                /* yes, poke it */
+                                /* Yes, poke it. This doesn't have to be atomic since
+                                 * the task is definitely not executing. */
                                 request_exit_np(t);
                         else if (!is_kernel_np(t))
                                 /* only if we are allowed to preempt the
                                  * currently-executing task */
                                 reschedule = 1;
                 } else {
-                        /* remote CPU case */
-                        if (is_user_np(t)) {
-                                /* need to notify user space of delayed
-                                 * preemption */
-
-                                /* to avoid a race, set the flag, then test
-                                 * again */
-                                request_exit_np(t);
-                                /* make sure it got written */
-                                mb();
-                        }
-                        /* Only send an ipi if remote task might have raced our
-                         * request, i.e., send an IPI to make sure in case it
-                         * exited its critical section.
-                         */
-                        reschedule = !is_np(t) && !is_kernel_np(t);
+                        /* Remote CPU case.  Only notify if it's not a kernel
+                         * NP section and if we didn't set the userspace
+                         * flag. */
+                        reschedule = !(is_kernel_np(t) || request_exit_np_atomic(t));
                 }
         }
         if (likely(reschedule))