From b75a22531588e77aa8c2daf228c9723916ae2cd0 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra
Date: Tue, 6 Oct 2015 14:36:17 +0200
Subject: sched/core: Better document the try_to_wake_up() barriers

Explain how the control dependency and smp_rmb() end up providing
ACQUIRE semantics and pair with smp_store_release() in
finish_lock_switch().

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/sched.h | 3 +++
 1 file changed, 3 insertions(+)

(limited to 'kernel/sched/sched.h')

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index efd3bfc7e347..b242775bf670 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1073,6 +1073,9 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
 	 * We must ensure this doesn't happen until the switch is completely
 	 * finished.
 	 *
+	 * In particular, the load of prev->state in finish_task_switch() must
+	 * happen before this.
+	 *
 	 * Pairs with the control dependency and rmb in try_to_wake_up().
 	 */
 	smp_store_release(&prev->on_cpu, 0);
-- 
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