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

From: Paul E. McKenney
Date: Fri Feb 03 2012 - 20:46:58 EST

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

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@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Kevin Hilman <khilman@xxxxxx>
Cc: Len Brown <len.brown@xxxxxxxxx>
Cc: Trinabh Gupta <g.trinabh@xxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Acked-by: Deepthi Dharwar <deepthi@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
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);
+ 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);
+ trace_power_end(dev->cpu);
+ trace_cpu_idle(PWR_EVENT_EXIT, dev->cpu);
+ );

if (entered_state >= 0) {
/* Update cpuidle counters */

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