[tip:sched/core] sched/core: Enable might_sleep() and smp_processor_id() checks early

[tip-bot for Thomas Gleixner <tipbot@zytor.com>]

Commit-ID:  1c3c5eab171590f86edd8d31389d61dd1efe3037
Gitweb:     http://git.kernel.org/tip/1c3c5eab171590f86edd8d31389d61dd1efe3037
Author:     Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Tue, 16 May 2017 20:42:48 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 23 May 2017 10:01:38 +0200

sched/core: Enable might_sleep() and smp_processor_id() checks early

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.

Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20170516184736.272225698@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 init/main.c            | 10 ++++++++++
 kernel/sched/core.c    |  4 +++-
 lib/smp_processor_id.c |  2 +-
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/init/main.c b/init/main.c
index badae3b..df58a41 100644
--- a/init/main.c
+++ b/init/main.c
@@ -414,6 +414,16 @@ static noinline void __ref rest_init(void)
 	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);
 
 	/*
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 877241e..c3e50ca 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6238,8 +6238,10 @@ void ___might_sleep(const char *file, int line, int preempt_offset)
 
 	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;
diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c
index 690d75b..2fb007b 100644
--- a/lib/smp_processor_id.c
+++ b/lib/smp_processor_id.c
@@ -28,7 +28,7 @@ notrace static unsigned int check_preemption_disabled(const char *what1,
 	/*
 	 * It is valid to assume CPU-locality during early bootup:
 	 */
-	if (system_state != SYSTEM_RUNNING)
+	if (system_state < SYSTEM_SCHEDULING)
 		goto out;
 
 	/*