linux-kernel - [PATCH] cpuidle: coupled: fix dead loop corner case

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Date:	Tue, 20 Aug 2013 13:17:44 +0800
From:	Neil Zhang <zhangwm@...vell.com>
To:	<rjw@...k.pl>, <daniel.lezcano@...aro.org>
CC:	<linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Neil Zhang <zhangwm@...vell.com>
Subject: [PATCH] cpuidle: coupled: fix dead loop corner case

There is a corener case when no peripheral irqs route to secondary
cores.
Let's take dual core system for example, the sequence is as following:

		Core 0			        Core1
1.			           set waiting bit and enter waiting loop
2. set waiting bit and poke core1
3. 				   clear poke in irq and enter safe state
4. set ready bit and enter ready loop

Since there is no peripheral irq route to core 1, so it will stay in
safe state forever, and core 0 will dead loop in the following code.
	while (!cpuidle_coupled_cpus_ready(coupled)) {
		/* Check if any other cpus bailed out of idle. */
		if (!cpuidle_coupled_cpus_waiting(coupled))
	}

The solution is don't let secondary core enter safe state when it has
already handled the poke interrupt.

Signed-off-by: Neil Zhang <zhangwm@...vell.com>
Reviewed-by: Fangsuo Wu <fswu@...vell.com>
---
 drivers/cpuidle/coupled.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/drivers/cpuidle/coupled.c b/drivers/cpuidle/coupled.c
index 2a297f8..a37c718 100644
--- a/drivers/cpuidle/coupled.c
+++ b/drivers/cpuidle/coupled.c
@@ -119,6 +119,7 @@ struct cpuidle_coupled {
 #define CPUIDLE_COUPLED_NOT_IDLE	(-1)
 
 static DEFINE_MUTEX(cpuidle_coupled_lock);
+static DEFINE_PER_CPU(bool, poke_sync);
 static DEFINE_PER_CPU(struct call_single_data, cpuidle_coupled_poke_cb);
 
 /*
@@ -295,6 +296,7 @@ static void cpuidle_coupled_poked(void *info)
 {
 	int cpu = (unsigned long)info;
 	cpumask_clear_cpu(cpu, &cpuidle_coupled_poked_mask);
+	__this_cpu_write(poke_sync, true);
 }
 
 /**
@@ -473,6 +475,7 @@ retry:
 	 * allowed for a single cpu.
 	 */
 	while (!cpuidle_coupled_cpus_waiting(coupled)) {
+		__this_cpu_write(poke_sync, false);
 		if (cpuidle_coupled_clear_pokes(dev->cpu)) {
 			cpuidle_coupled_set_not_waiting(dev->cpu, coupled);
 			goto out;
@@ -483,6 +486,10 @@ retry:
 			goto out;
 		}
 
+		if (cpuidle_coupled_cpus_waiting(coupled)
+			&& __this_cpu_read(poke_sync))
+			break;
+
 		entered_state = cpuidle_enter_state(dev, drv,
 			dev->safe_state_index);
 	}
-- 
1.7.4.1

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