Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler fix from Thomas Gleixner:
"A single scheduler fix:
Prevent idle task from ever being preempted. That makes sure that
synchronize_rcu_tasks() which is ignoring idle task does not pretend
that no task is stuck in preempted state. If that happens and idle was
preempted on a ftrace trampoline the machine crashes due to
inconsistent state"
* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched/core: Call __schedule() from do_idle() without enabling preemption
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 759f4bd..803c3bc 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3502,6 +3502,31 @@
}
EXPORT_SYMBOL(schedule);
+/*
+ * synchronize_rcu_tasks() makes sure that no task is stuck in preempted
+ * state (have scheduled out non-voluntarily) by making sure that all
+ * tasks have either left the run queue or have gone into user space.
+ * As idle tasks do not do either, they must not ever be preempted
+ * (schedule out non-voluntarily).
+ *
+ * schedule_idle() is similar to schedule_preempt_disable() except that it
+ * never enables preemption because it does not call sched_submit_work().
+ */
+void __sched schedule_idle(void)
+{
+ /*
+ * As this skips calling sched_submit_work(), which the idle task does
+ * regardless because that function is a nop when the task is in a
+ * TASK_RUNNING state, make sure this isn't used someplace that the
+ * current task can be in any other state. Note, idle is always in the
+ * TASK_RUNNING state.
+ */
+ WARN_ON_ONCE(current->state);
+ do {
+ __schedule(false);
+ } while (need_resched());
+}
+
#ifdef CONFIG_CONTEXT_TRACKING
asmlinkage __visible void __sched schedule_user(void)
{
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 2a25a9e..ef63adc 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -265,7 +265,7 @@
smp_mb__after_atomic();
sched_ttwu_pending();
- schedule_preempt_disabled();
+ schedule_idle();
if (unlikely(klp_patch_pending(current)))
klp_update_patch_state(current);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 7808ab0..6dda2aa 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1467,6 +1467,8 @@
}
#endif
+extern void schedule_idle(void);
+
extern void sysrq_sched_debug_show(void);
extern void sched_init_granularity(void);
extern void update_max_interval(void);
