linux-kernel - [PATCH tip/core/rcu 47/47] cpuidle: Inform RCU of read-side critical sections

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Date:	Fri,  3 Feb 2012 17:45:22 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Kevin Hilman <khilman@...com>, Len Brown <len.brown@...el.com>,
	Trinabh Gupta <g.trinabh@...il.com>,
	Arjan van de Ven <arjan@...ux.intel.com>
Subject: [PATCH tip/core/rcu 47/47] cpuidle: Inform RCU of read-side critical sections

From: "Paul E. McKenney" <paul.mckenney@...aro.org>

The cpuidle_idle_call() function is invoked in the inner idle loop,
after the call to rcu_idle_enter() and before the call to rcu_idle_exit().
This means that RCU is ignoring the CPU at this point.  Unfortunately,
cpuidle_idle_call() nevertheless contains tracepoints (important ones
used by powertop) that expect RCU to be paying attention.  The consequences
of using RCU read-side critical sections on CPUs that RCU is ignoring
can be severe, including random corruption of random memory.

Therefore, this commit uses the new RCU_NONIDLE() macro to let RCU
do its job with respect to the tracepoints.

Suggested-by: Nicolas Pitre <nicolas.pitre@...aro.org>
Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Kevin Hilman <khilman@...com>
Cc: Len Brown <len.brown@...el.com>
Cc: Trinabh Gupta <g.trinabh@...il.com>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Acked-by: Deepthi Dharwar <deepthi@...ux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@...htriplett.org>
---
 drivers/cpuidle/cpuidle.c |   12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 59f4261..cd8a553 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -94,13 +94,17 @@ int cpuidle_idle_call(void)
 
 	target_state = &drv->states[next_state];
 
-	trace_power_start(POWER_CSTATE, next_state, dev->cpu);
-	trace_cpu_idle(next_state, dev->cpu);
+	RCU_NONIDLE(
+		trace_power_start(POWER_CSTATE, next_state, dev->cpu);
+		trace_cpu_idle(next_state, dev->cpu)
+	);
 
 	entered_state = target_state->enter(dev, drv, next_state);
 
-	trace_power_end(dev->cpu);
-	trace_cpu_idle(PWR_EVENT_EXIT, dev->cpu);
+	RCU_NONIDLE(
+		trace_power_end(dev->cpu);
+		trace_cpu_idle(PWR_EVENT_EXIT, dev->cpu);
+	);
 
 	if (entered_state >= 0) {
 		/* Update cpuidle counters */
-- 
1.7.8

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