linux-kernel - [PATCH 2/2] cpuidle: coupled: fix decrementing ready count

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Date:	Fri, 18 May 2012 11:05:24 -0700
From:	Colin Cross <ccross@...roid.com>
To:	Len Brown <len.brown@...el.com>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-pm@...ts.linux-foundation.org, Kevin Hilman <khilman@...com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Deepthi Dharwar <deepthi@...ux.vnet.ibm.com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Amit Kucheria <amit.kucheria@...aro.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Colin Cross <ccross@...roid.com>
Subject: [PATCH 2/2] cpuidle: coupled: fix decrementing ready count

cpuidle_coupled_set_not_ready sometimes refuses to decrement the
ready count in order to prevent a race condition.  This makes it
unsuitable for use when finished with idle.  Add a new function
cpuidle_coupled_set_done that decrements both the ready count and
waiting count, and call it after idle is complete.

Signed-off-by: Colin Cross <ccross@...roid.com>
---
 drivers/cpuidle/coupled.c |   18 ++++++++++++++++--
 1 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/cpuidle/coupled.c b/drivers/cpuidle/coupled.c
index b02810a..fc427fa 100644
--- a/drivers/cpuidle/coupled.c
+++ b/drivers/cpuidle/coupled.c
@@ -388,6 +388,21 @@ static void cpuidle_coupled_set_not_waiting(int cpu,
 }
 
 /**
+ * cpuidle_coupled_set_done - mark this cpu as leaving the ready loop
+ * @cpu: the current cpu
+ * @coupled: the struct coupled that contains the current cpu
+ *
+ * Marks this cpu as no longer in the ready and waiting loops.  Decrements
+ * the waiting count first to prevent another cpu looping back in and seeing
+ * this cpu as waiting just before it exits idle.
+ */
+static void cpuidle_coupled_set_done(int cpu, struct cpuidle_coupled *coupled)
+{
+	cpuidle_coupled_set_not_waiting(cpu, coupled);
+	atomic_sub(MAX_WAITING_CPUS, &coupled->ready_waiting_counts);
+}
+
+/**
  * cpuidle_coupled_clear_pokes - spin until the poke interrupt is processed
  * @cpu - this cpu
  *
@@ -501,8 +516,7 @@ int cpuidle_enter_state_coupled(struct cpuidle_device *dev,
 
 	entered_state = cpuidle_enter_state(dev, drv, next_state);
 
-	cpuidle_coupled_set_not_waiting(dev->cpu, coupled);
-	cpuidle_coupled_set_not_ready(coupled);
+	cpuidle_coupled_set_done(dev->cpu, coupled);
 
 out:
 	/*
-- 
1.7.7.3

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