linux-kernel - [PATCH 3/5] rcuwait: Introduce prepare_to and finish

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Date:   Tue, 21 Apr 2020 21:07:37 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     tglx@...utronix.de, pbonzini@...hat.com
Cc:     bigeasy@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        torvalds@...ux-foundation.org, will@...nel.org,
        joel@...lfernandes.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, dave@...olabs.net,
        Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 3/5] rcuwait: Introduce prepare_to and finish_rcuwait

This allows further flexibility for some callers to implement
ad-hoc versions of the generic rcuwait_wait_event(). For example,
kvm will need this to maintain tracing semantics. The naming
is of course similar to what waitqueue apis offer.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 include/linux/rcuwait.h | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/include/linux/rcuwait.h b/include/linux/rcuwait.h
index 6ebb23258a27..0c6a3d0d25ab 100644
--- a/include/linux/rcuwait.h
+++ b/include/linux/rcuwait.h
@@ -29,12 +29,25 @@ extern int rcuwait_wake_up(struct rcuwait *w);
 
 /*
  * The caller is responsible for locking around rcuwait_wait_event(),
- * such that writes to @task are properly serialized.
+ * and prepare_to_rcuwait() such that writes to @task are properly
+ * serialized.
  */
+
+static inline void prepare_to_rcuwait(struct rcuwait *w)
+{
+	rcu_assign_pointer(w->task, current);
+}
+
+static inline void finish_rcuwait(struct rcuwait *w)
+{
+	WRITE_ONCE(w->task, NULL);
+	__set_current_state(TASK_RUNNING);
+}
+
 #define rcuwait_wait_event(w, condition, state)				\
 ({									\
 	int __ret = 0;							\
-	rcu_assign_pointer((w)->task, current);				\
+	prepare_to_rcuwait(w);						\
 	for (;;) {							\
 		/*							\
 		 * Implicit barrier (A) pairs with (B) in		\
@@ -51,9 +64,7 @@ extern int rcuwait_wake_up(struct rcuwait *w);
 									\
 		schedule();						\
 	}								\
-									\
-	WRITE_ONCE((w)->task, NULL);					\
-	__set_current_state(TASK_RUNNING);				\
+	finish_rcuwait(w);						\
 	__ret;								\
 })
 
-- 
2.16.4