[patch V2 17/17] sched: Enable might_sleep() and smp_processor_id() checks early

[Thomas Gleixner]

might_sleep() and smp_processor_id() checks are enabled after the boot
process is done. That hides bugs in the smp bringup and driver
initialization code.

Enable it right when the scheduler starts working, i.e. when init task and
kthreadd have been created and right before the idle task enables
preemption.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 init/main.c            |   10 ++++++++++
 kernel/sched/core.c    |    4 +++-
 lib/smp_processor_id.c |    2 +-
 3 files changed, 14 insertions(+), 2 deletions(-)

--- a/init/main.c
+++ b/init/main.c
@@ -414,6 +414,16 @@ static noinline void __ref rest_init(voi
 	rcu_read_lock();
 	kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
 	rcu_read_unlock();
+
+	/*
+	 * Enable might_sleep() and smp_processor_id() checks.
+	 * They cannot be enabled earlier because with CONFIG_PRREMPT=y
+	 * kernel_thread() would trigger might_sleep() splats. With
+	 * CONFIG_PREEMPT_VOLUNTARY=y the init task might have scheduled
+	 * already, but it's stuck on the kthreadd_done completion.
+	 */
+	system_state = SYSTEM_SCHEDULING;
+
 	complete(&kthreadd_done);
 
 	/*
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6226,8 +6226,10 @@ void ___might_sleep(const char *file, in
 
 	if ((preempt_count_equals(preempt_offset) && !irqs_disabled() &&
 	     !is_idle_task(current)) ||
-	    system_state != SYSTEM_RUNNING || oops_in_progress)
+	    system_state == SYSTEM_BOOTING || system_state > SYSTEM_RUNNING ||
+	    oops_in_progress)
 		return;
+
 	if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
 		return;
 	prev_jiffy = jiffies;
--- a/lib/smp_processor_id.c
+++ b/lib/smp_processor_id.c
@@ -28,7 +28,7 @@ notrace static unsigned int check_preemp
 	/*
 	 * It is valid to assume CPU-locality during early bootup:
 	 */
-	if (system_state != SYSTEM_RUNNING)
+	if (system_state < SYSTEM_SCHEDULING)
 		goto out;
 
 	/*