linux-kernel - [PATCH 2/2] cpufreq: Guard against not-yet-initialized policies in cpufreq_cpu

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Message-Id: <1414510008-7262-2-git-send-email-tomeu.vizoso@collabora.com>
Date:	Tue, 28 Oct 2014 16:26:48 +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 2/2] 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:

[    4.651435] ------------[ cut here ]------------
[    4.651453] WARNING: CPU: 1 PID: 64 at include/linux/kref.h:47 kobject_get+0x64/0x70()
[    4.651463] Modules linked in:
[    4.651473] CPU: 1 PID: 64 Comm: irq/77-tegra-ac Not tainted 3.18.0-rc1-next-20141027ccu-00049-g21a0041 #248
[    4.651497] [<c0016fac>] (unwind_backtrace) from [<c001272c>] (show_stack+0x10/0x14)
[    4.651505] [<c001272c>] (show_stack) from [<c0601920>] (dump_stack+0x98/0xd8)
[    4.651515] [<c0601920>] (dump_stack) from [<c00288d8>] (warn_slowpath_common+0x70/0x8c)
[    4.651522] [<c00288d8>] (warn_slowpath_common) from [<c0028990>] (warn_slowpath_null+0x1c/0x24)
[    4.651530] [<c0028990>] (warn_slowpath_null) from [<c02227bc>] (kobject_get+0x64/0x70)
[    4.651539] [<c02227bc>] (kobject_get) from [<c03e5238>] (cpufreq_cpu_get+0x88/0xc8)
[    4.651547] [<c03e5238>] (cpufreq_cpu_get) from [<c03e52ec>] (cpufreq_get+0xc/0x64)
[    4.651555] [<c03e52ec>] (cpufreq_get) from [<c0287818>] (actmon_thread_isr+0x140/0x1a4)
[    4.651563] [<c0287818>] (actmon_thread_isr) from [<c0068a68>] (irq_thread_fn+0x1c/0x40)
[    4.651570] [<c0068a68>] (irq_thread_fn) from [<c0068d84>] (irq_thread+0x134/0x174)
[    4.651579] [<c0068d84>] (irq_thread) from [<c0040284>] (kthread+0xdc/0xf4)
[    4.651587] [<c0040284>] (kthread) from [<c000f4b8>] (ret_from_fork+0x14/0x3c)
[    4.651591] ---[ end trace 7f6a15d1272e6ef3 ]---

This commit checks that the policy object has been initialized already before
trying to ref it.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
---
 drivers/cpufreq/cpufreq.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 644b54e..37cd6c9 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -214,8 +214,12 @@ struct cpufreq_policy *cpufreq_cpu_get(unsigned int cpu)
 	if (cpufreq_driver) {
 		/* get the CPU */
 		policy = per_cpu(cpufreq_cpu_data, cpu);
-		if (policy)
-			kobject_get(&policy->kobj);
+		if (policy) {
+			if (!kobject_initialized(&policy->kobj))
+				policy = NULL;
+			else
+				kobject_get(&policy->kobj);
+		}
 	}
 
 	read_unlock_irqrestore(&cpufreq_driver_lock, flags);
-- 
1.9.3

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