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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
Message-Id: <20200424054837.5138-5-dave@stgolabs.net>
In-Reply-To: <20200424054837.5138-1-dave@stgolabs.net>
References: <20200424054837.5138-1-dave@stgolabs.net>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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