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From: qiwuchen55@gmail.com
To: mmayer@broadcom.com, rjw@rjwysocki.net, viresh.kumar@linaro.org,
	f.fainelli@gmail.com
Cc: bcm-kernel-feedback-list@broadcom.com, linux-pm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	chenqiwu <chenqiwu@xiaomi.com>
Subject: [PATCH v4] cpufreq: brcmstb-avs: fix imbalance of cpufreq policy refcount
Date: Mon, 20 Jan 2020 15:41:28 +0800	[thread overview]
Message-ID: <1579506088-6736-1-git-send-email-qiwuchen55@gmail.com> (raw)

From: chenqiwu <chenqiwu@xiaomi.com>

brcm_avs_cpufreq_get() calls cpufreq_cpu_get() to get the cpufreq
policy, meanwhile, it also increments the kobject reference count
to mark it busy. However, a corresponding call of cpufreq_cpu_put()
is ignored to decrement the kobject reference count back, which may
lead to a potential stuck risk that the cpuhp thread deadly waits
for dropping of kobject refcount when cpufreq policy free.

With this patch, the cpuhp thread can be easily exercised by
attempting to force an unbind of the CPUfreq driver.

Signed-off-by: chenqiwu <chenqiwu@xiaomi.com>
---
changes in v4:
 - Rewrit commit message.
 - Use cpufreq_cpu_get() and a corresponding cpufreq_cpu_put()
   instead of cpufreq_get_policy() for promoting efficiency.
---
 drivers/cpufreq/brcmstb-avs-cpufreq.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/brcmstb-avs-cpufreq.c b/drivers/cpufreq/brcmstb-avs-cpufreq.c
index 77b0e5d..0767206 100644
--- a/drivers/cpufreq/brcmstb-avs-cpufreq.c
+++ b/drivers/cpufreq/brcmstb-avs-cpufreq.c
@@ -453,7 +453,13 @@ static bool brcm_avs_is_firmware_loaded(struct private_data *priv)
 static unsigned int brcm_avs_cpufreq_get(unsigned int cpu)
 {
 	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
-	struct private_data *priv = policy->driver_data;
+	struct private_data *priv;
+
+	if (!policy)
+		return 0;
+
+	priv = policy->driver_data;
+	cpufreq_cpu_put(policy);
 
 	return brcm_avs_get_frequency(priv->base);
 }
-- 
1.9.1


WARNING: multiple messages have this Message-ID (diff)
From: qiwuchen55@gmail.com
To: mmayer@broadcom.com, rjw@rjwysocki.net, viresh.kumar@linaro.org,
	f.fainelli@gmail.com
Cc: chenqiwu <chenqiwu@xiaomi.com>,
	bcm-kernel-feedback-list@broadcom.com,
	linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org
Subject: [PATCH v4] cpufreq: brcmstb-avs: fix imbalance of cpufreq policy refcount
Date: Mon, 20 Jan 2020 15:41:28 +0800	[thread overview]
Message-ID: <1579506088-6736-1-git-send-email-qiwuchen55@gmail.com> (raw)

From: chenqiwu <chenqiwu@xiaomi.com>

brcm_avs_cpufreq_get() calls cpufreq_cpu_get() to get the cpufreq
policy, meanwhile, it also increments the kobject reference count
to mark it busy. However, a corresponding call of cpufreq_cpu_put()
is ignored to decrement the kobject reference count back, which may
lead to a potential stuck risk that the cpuhp thread deadly waits
for dropping of kobject refcount when cpufreq policy free.

With this patch, the cpuhp thread can be easily exercised by
attempting to force an unbind of the CPUfreq driver.

Signed-off-by: chenqiwu <chenqiwu@xiaomi.com>
---
changes in v4:
 - Rewrit commit message.
 - Use cpufreq_cpu_get() and a corresponding cpufreq_cpu_put()
   instead of cpufreq_get_policy() for promoting efficiency.
---
 drivers/cpufreq/brcmstb-avs-cpufreq.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/brcmstb-avs-cpufreq.c b/drivers/cpufreq/brcmstb-avs-cpufreq.c
index 77b0e5d..0767206 100644
--- a/drivers/cpufreq/brcmstb-avs-cpufreq.c
+++ b/drivers/cpufreq/brcmstb-avs-cpufreq.c
@@ -453,7 +453,13 @@ static bool brcm_avs_is_firmware_loaded(struct private_data *priv)
 static unsigned int brcm_avs_cpufreq_get(unsigned int cpu)
 {
 	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
-	struct private_data *priv = policy->driver_data;
+	struct private_data *priv;
+
+	if (!policy)
+		return 0;
+
+	priv = policy->driver_data;
+	cpufreq_cpu_put(policy);
 
 	return brcm_avs_get_frequency(priv->base);
 }
-- 
1.9.1


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             reply	other threads:[~2020-01-20  7:41 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-20  7:41 qiwuchen55 [this message]
2020-01-20  7:41 ` [PATCH v4] cpufreq: brcmstb-avs: fix imbalance of cpufreq policy refcount qiwuchen55
2020-01-20  7:54 ` Viresh Kumar
2020-01-20  7:54   ` Viresh Kumar

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