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Message-ID: <558439df-9f0e-9c2a-6332-64e3e2a5c823@huawei.com>
Date: Wed, 1 Dec 2021 09:29:37 +0800
From: Xiongfeng Wang <wangxiongfeng2@...wei.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>,
Viresh Kumar <viresh.kumar@...aro.org>
CC: Linux PM <linux-pm@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Hanjun Guo <guohanjun@...wei.com>
Subject: Re: [PATCH] cpufreq: Fix get_cpu_device() failed in
add_cpu_dev_symlink()
Hi,
On 2021/11/30 19:42, Rafael J. Wysocki wrote:
> On Mon, Nov 29, 2021 at 10:10 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>>
>> 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@...wei.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 :(
>
> This is the real hot-add path which isn't tested on a regular basis.
>
>> Anyway the patch is okay,
>
> It would be good to add a Fixes: tag to it, though. Any idea about
> the commit this should point to?
When I look up the commit history, I found this one.
2f0ba790df51 ("cpufreq: Fix creation of symbolic links to policy directories")
Before this commit, the 'dev' is passed to add_cpu_dev_symlink() in
cpufreq_add_dev(). Maybe we can point to this one.
>
>> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> .
>
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