Date:   Mon, 29 Nov 2021 14:40:39 +0530
From:   Viresh Kumar <viresh.kumar@linaro.org>
To:     Xiongfeng Wang <wangxiongfeng2@huawei.com>
Cc:     rafael@kernel.org, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org, guohanjun@huawei.com
Subject: Re: [PATCH] cpufreq: Fix get_cpu_device() failed in
 add_cpu_dev_symlink()
Message-ID: <20211129091039.s7bqq43o4ktuub6t@vireshk-i7>
References: <20211129080248.46240-1-wangxiongfeng2@huawei.com>
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On 29-11-21, 16:02, Xiongfeng Wang wrote:
> When I hot added a CPU, I found 'cpufreq' directory is 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 stack
> 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().
> 
> Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
> ---
>  drivers/cpufreq/cpufreq.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index e338d2f010fe..22aa2793e4d2 100644
> --- 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 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;
>  }

Interesting that I never hit it earlier despite doing rigorous testing of
hotplug stuff :(

Anyway the patch is okay,

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

-- 
viresh