linux-kernel - [PATCH 5.10 035/130] cpufreq: Fix get_cpu_device() failure in add_cpu_dev

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Date:   Mon,  6 Dec 2021 15:55:52 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Xiongfeng Wang <wangxiongfeng2@...wei.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: [PATCH 5.10 035/130] cpufreq: Fix get_cpu_device() failure in add_cpu_dev_symlink()

From: Xiongfeng Wang <wangxiongfeng2@...wei.com>

commit 2c1b5a84669d2477d8fffe9136e86a2cff591729 upstream.

When I hot added a CPU, I found 'cpufreq' directory was not created
below /sys/devices/system/cpu/cpuX/.

It is because get_cpu_device() failed in add_cpu_dev_symlink().

cpufreq_add_dev() is the .add_dev callback of a CPU subsys interface.
It will be called when the CPU device registered into the system.
The call chain is as follows:

  register_cpu()
  ->device_register()
   ->device_add()
    ->bus_probe_device()
     ->cpufreq_add_dev()

But only after the CPU device has been registered, we can get the
CPU device by get_cpu_device(), otherwise it will return NULL.

Since we already have the CPU device in cpufreq_add_dev(), pass
it to add_cpu_dev_symlink().

I noticed that the 'kobj' of the CPU device has been added into
the system before cpufreq_add_dev().

Fixes: 2f0ba790df51 ("cpufreq: Fix creation of symbolic links to policy directories")
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@...wei.com>
Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
Cc: All applicable <stable@...r.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/cpufreq/cpufreq.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1004,10 +1004,9 @@ static struct kobj_type ktype_cpufreq =
 	.release	= cpufreq_sysfs_release,
 };
 
-static void add_cpu_dev_symlink(struct cpufreq_policy *policy, unsigned int cpu)
+static void add_cpu_dev_symlink(struct cpufreq_policy *policy, unsigned int cpu,
+				struct device *dev)
 {
-	struct device *dev = get_cpu_device(cpu);
-
 	if (unlikely(!dev))
 		return;
 
@@ -1391,7 +1390,7 @@ static int cpufreq_online(unsigned int c
 	if (new_policy) {
 		for_each_cpu(j, policy->related_cpus) {
 			per_cpu(cpufreq_cpu_data, j) = policy;
-			add_cpu_dev_symlink(policy, j);
+			add_cpu_dev_symlink(policy, j, get_cpu_device(j));
 		}
 
 		policy->min_freq_req = kzalloc(2 * sizeof(*policy->min_freq_req),
@@ -1553,7 +1552,7 @@ static int cpufreq_add_dev(struct device
 	/* Create sysfs link on CPU registration */
 	policy = per_cpu(cpufreq_cpu_data, cpu);
 	if (policy)
-		add_cpu_dev_symlink(policy, cpu);
+		add_cpu_dev_symlink(policy, cpu, dev);
 
 	return 0;
 }