FAILED: patch "[PATCH] cpufreq: Fix get_cpu_device() failure in" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2c1b5a84669d2477d8fffe9136e86a2cff591729 Mon Sep 17 00:00:00 2001
From: Xiongfeng Wang <[email protected]>
Date: Mon, 29 Nov 2021 16:02:48 +0800
Subject: [PATCH] cpufreq: Fix get_cpu_device() failure in
add_cpu_dev_symlink()

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().

index e338d2f010fe..22aa2793e4d2 100644
@@ -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 cpu)
 	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),

@@ -1565,7 +1564,7 @@ static int cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
 	/* 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;
 }