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From: Davidlohr Bueso <dave@stgolabs.net>
To: tglx@linutronix.de, pbonzini@redhat.com
Cc: peterz@infradead.org, maz@kernel.org, bigeasy@linutronix.de,
	rostedt@goodmis.org, torvalds@linux-foundation.org,
	will@kernel.org, joel@joelfernandes.org,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	dave@stgolabs.net, Davidlohr Bueso <dbueso@suse.de>
Subject: [PATCH 3/5] rcuwait: Introduce prepare_to and finish_rcuwait
Date: Thu, 23 Apr 2020 22:48:35 -0700	[thread overview]
Message-ID: <20200424054837.5138-4-dave@stgolabs.net> (raw)
In-Reply-To: <20200424054837.5138-1-dave@stgolabs.net>

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.

Also go ahead and make use of rcu_assign_pointer() for both task
writes as it will make the __rcu sparse people happy - this will
be the special nil case, thus no added serialization.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Davidlohr Bueso <dbueso@suse.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..45bc6604e9b1 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/finish]_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)
+{
+        rcu_assign_pointer(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


  parent reply	other threads:[~2020-04-24  5:52 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-24  5:48 [PATCH v4 0/5] kvm: Use rcuwait for vcpu blocking Davidlohr Bueso
2020-04-24  5:48 ` [PATCH 1/5] rcuwait: Fix stale wake call name in comment Davidlohr Bueso
2020-04-24  5:48 ` [PATCH 2/5] rcuwait: Let rcuwait_wake_up() return whether or not a task was awoken Davidlohr Bueso
2020-04-24  5:48 ` Davidlohr Bueso [this message]
2020-04-24  5:48 ` [PATCH 4/5] rcuwait: Introduce rcuwait_active() Davidlohr Bueso
2020-04-24  9:55   ` Peter Zijlstra
2020-05-18 10:33   ` Paolo Bonzini
2020-05-18 16:37     ` Davidlohr Bueso
2020-05-19  0:34     ` Wanpeng Li
2020-04-24  5:48 ` [PATCH 5/5] kvm: Replace vcpu->swait with rcuwait Davidlohr Bueso
2020-04-25 10:24   ` Paolo Bonzini
2020-04-25 22:30     ` Davidlohr Bueso
2020-05-18  8:51   ` Wanpeng Li
  -- strict thread matches above, loose matches on Subject: below --
2020-04-22  4:07 [PATCH v3 -tip 0/5] kvm: Use rcuwait for vcpu blocking Davidlohr Bueso
2020-04-22  4:07 ` [PATCH 3/5] rcuwait: Introduce prepare_to and finish_rcuwait Davidlohr Bueso
2020-04-23  9:23   ` Peter Zijlstra

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