linux-kernel - [PATCH v2] cpufreq: Guard against not-yet-initialized policies in cpufreq_cpu

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Date:	Wed, 29 Oct 2014 16:45:47 +0100
From:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:	linux-kernel@...r.kernel.org
Cc:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	linux-pm@...r.kernel.org
Subject: [PATCH v2] cpufreq: Guard against not-yet-initialized policies in cpufreq_cpu_get()

There's a substantial window of opportunity from the time the policy objects
are created until they are initialized, causing this:

WARNING: CPU: 1 PID: 64 at include/linux/kref.h:47 kobject_get+0x64/0x70()
Modules linked in:
CPU: 1 PID: 64 Comm: irq/77-tegra-ac Not tainted 3.18.0-rc1-next-20141027ccu-00049-g21a0041 #248
[<c0016fac>] (unwind_backtrace) from [<c001272c>] (show_stack+0x10/0x14)
[<c001272c>] (show_stack) from [<c0601920>] (dump_stack+0x98/0xd8)
[<c0601920>] (dump_stack) from [<c00288d8>] (warn_slowpath_common+0x70/0x8c)
[<c00288d8>] (warn_slowpath_common) from [<c0028990>] (warn_slowpath_null+0x1c/0x24)
[<c0028990>] (warn_slowpath_null) from [<c02227bc>] (kobject_get+0x64/0x70)
[<c02227bc>] (kobject_get) from [<c03e5238>] (cpufreq_cpu_get+0x88/0xc8)
[<c03e5238>] (cpufreq_cpu_get) from [<c03e52ec>] (cpufreq_get+0xc/0x64)
[<c03e52ec>] (cpufreq_get) from [<c0287818>] (actmon_thread_isr+0x140/0x1a4)
[<c0287818>] (actmon_thread_isr) from [<c0068a68>] (irq_thread_fn+0x1c/0x40)
[<c0068a68>] (irq_thread_fn) from [<c0068d84>] (irq_thread+0x134/0x174)
[<c0068d84>] (irq_thread) from [<c0040284>] (kthread+0xdc/0xf4)
[<c0040284>] (kthread) from [<c000f4b8>] (ret_from_fork+0x14/0x3c)

This commit checks that initialization has finished before trying to do
anything with the policy.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
---
 drivers/cpufreq/cpufreq.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 644b54e..7b84d1a 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -48,6 +48,9 @@ static DEFINE_PER_CPU(char[CPUFREQ_NAME_LEN], cpufreq_cpu_governor);
 /* Flag to suspend/resume CPUFreq governors */
 static bool cpufreq_suspended;
 
+/* Flag that tells whether initialization is completed */
+static atomic_t cpufreq_initialized = ATOMIC_INIT(0);
+
 static inline bool has_target(void)
 {
 	return cpufreq_driver->target_index || cpufreq_driver->target;
@@ -211,7 +214,7 @@ struct cpufreq_policy *cpufreq_cpu_get(unsigned int cpu)
 	/* get the cpufreq driver */
 	read_lock_irqsave(&cpufreq_driver_lock, flags);
 
-	if (cpufreq_driver) {
+	if (atomic_read(&cpufreq_initialized)) {
 		/* get the CPU */
 		policy = per_cpu(cpufreq_cpu_data, cpu);
 		if (policy)
@@ -1289,6 +1292,8 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
 	kobject_uevent(&policy->kobj, KOBJ_ADD);
 	up_read(&cpufreq_rwsem);
 
+	atomic_set(&cpufreq_initialized, 1);
+
 	pr_debug("initialization complete\n");
 
 	return 0;
-- 
1.9.3

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