On Mon, Nov 29, 2021 at 10:10 AM Viresh Kumar [off-list ref] wrote:

On 29-11-21, 16:02, Xiongfeng Wang wrote:

quoted

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 <redacted>
---
 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?

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