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

Pull scheduler fixes from Ingo Molnar:
 "Two fixes: one for a lost wakeup, the other to fix the compiler
  optimizing out preempt operations on ARM64 (and possibly other non-x86
  architectures)"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/core: Fix remote wakeups
  sched/preempt: Fix preempt_count manipulations

3 files changed, 14 insertions, 9 deletions

diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h
index 5d8ffa3e6f8c..c1cde3577551 100644
--- a/include/asm-generic/preempt.h
+++ b/include/asm-generic/preempt.h
@@ -7,10 +7,10 @@
 
 static __always_inline int preempt_count(void)
 {
-        return current_thread_info()->preempt_count;
+        return READ_ONCE(current_thread_info()->preempt_count);
 }
 
-static __always_inline int *preempt_count_ptr(void)
+static __always_inline volatile int *preempt_count_ptr(void)
 {
         return &current_thread_info()->preempt_count;
 }
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 21c26e78aec5..23e075dcdfe4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1539,6 +1539,7 @@ struct task_struct {
         unsigned sched_reset_on_fork:1;
         unsigned sched_contributes_to_load:1;
         unsigned sched_migrated:1;
+        unsigned sched_remote_wakeup:1;
         unsigned :0; /* force alignment to the next boundary */
 
         /* unserialized, strictly 'current' */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 404c0784b1fc..7f2cae4620c7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1768,13 +1768,15 @@ void sched_ttwu_pending(void)
         cookie = lockdep_pin_lock(&rq->lock);
 
         while (llist) {
+                int wake_flags = 0;
+
                 p = llist_entry(llist, struct task_struct, wake_entry);
                 llist = llist_next(llist);
-                /*
-                 * See ttwu_queue(); we only call ttwu_queue_remote() when
-                 * its a x-cpu wakeup.
-                 */
-                ttwu_do_activate(rq, p, WF_MIGRATED, cookie);
+
+                if (p->sched_remote_wakeup)
+                        wake_flags = WF_MIGRATED;
+
+                ttwu_do_activate(rq, p, wake_flags, cookie);
         }
 
         lockdep_unpin_lock(&rq->lock, cookie);
@@ -1819,10 +1821,12 @@ void scheduler_ipi(void)
         irq_exit();
 }
 
-static void ttwu_queue_remote(struct task_struct *p, int cpu)
+static void ttwu_queue_remote(struct task_struct *p, int cpu, int wake_flags)
 {
         struct rq *rq = cpu_rq(cpu);
 
+        p->sched_remote_wakeup = !!(wake_flags & WF_MIGRATED);
+
         if (llist_add(&p->wake_entry, &cpu_rq(cpu)->wake_list)) {
                 if (!set_nr_if_polling(rq->idle))
                         smp_send_reschedule(cpu);
@@ -1869,7 +1873,7 @@ static void ttwu_queue(struct task_struct *p, int cpu, int wake_flags)
 #if defined(CONFIG_SMP)
         if (sched_feat(TTWU_QUEUE) && !cpus_share_cache(smp_processor_id(), cpu)) {
                 sched_clock_cpu(cpu); /* sync clocks x-cpu */
-                ttwu_queue_remote(p, cpu);
+                ttwu_queue_remote(p, cpu, wake_flags);
                 return;
         }
 #endif