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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 4/5] rcuwait: Introduce rcuwait_active()
Date: Thu, 23 Apr 2020 22:48:36 -0700	[thread overview]
Message-ID: <20200424054837.5138-5-dave@stgolabs.net> (raw)
In-Reply-To: <20200424054837.5138-1-dave@stgolabs.net>

This call is lockless and thus should not be trustedblindly,
ie: for wakeup purposes, which is already provided correctly
by rcuwait_wakeup().

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
 include/linux/rcuwait.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/include/linux/rcuwait.h b/include/linux/rcuwait.h
index 45bc6604e9b1..c1414ce44abc 100644
--- a/include/linux/rcuwait.h
+++ b/include/linux/rcuwait.h
@@ -25,6 +25,15 @@ static inline void rcuwait_init(struct rcuwait *w)
 	w->task = NULL;
 }
 
+/*
+ * Note: this provides no serialization and, just as with waitqueues,
+ * requires care to estimate as to whether or not the wait is active.
+ */
+static inline int rcuwait_active(struct rcuwait *w)
+{
+	return !!rcu_dereference(w->task);
+}
+
 extern int rcuwait_wake_up(struct rcuwait *w);
 
 /*
-- 
2.16.4


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

Thread overview: 17+ 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 ` [PATCH 3/5] rcuwait: Introduce prepare_to and finish_rcuwait Davidlohr Bueso
2020-04-24  5:48 ` Davidlohr Bueso [this message]
2020-04-24  9:55   ` [PATCH 4/5] rcuwait: Introduce rcuwait_active() 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
2020-04-24  5:48   ` Davidlohr Bueso
2020-04-25 10:24   ` Paolo Bonzini
2020-04-25 10:24     ` Paolo Bonzini
2020-04-25 22:30     ` Davidlohr Bueso
2020-04-25 22:30       ` Davidlohr Bueso
2020-05-18  8:51   ` Wanpeng Li
2020-05-18  8:51     ` Wanpeng Li

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