Message-ID: <CAJZ5v0g__9g_dfA3=4GVi351f4CKBegKkW9nU81j+Qu=2Hfg1Q@mail.gmail.com>
Date: Thu, 4 Sep 2025 15:17:26 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Zihuan Zhang <zhangzihuan@...inos.cn>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Viresh Kumar <viresh.kumar@...aro.org>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
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Subject: Re: [PATCH v4 07/10] powercap: dtpm_cpu: Use scope-based cleanup helper

On Thu, Sep 4, 2025 at 12:38 PM Zihuan Zhang <zhangzihuan@...inos.cn> wrote:
>
>
> 在 2025/9/3 21:45, Rafael J. Wysocki 写道:
> > On Wed, Sep 3, 2025 at 3:18 PM Zihuan Zhang <zhangzihuan@...inos.cn> wrote:
> >> Replace the manual cpufreq_cpu_put() with __free(put_cpufreq_policy)
> >> annotation for policy references. This reduces the risk of reference
> >> counting mistakes and aligns the code with the latest kernel style.
> >>
> >> No functional change intended.
> >>
> >> Signed-off-by: Zihuan Zhang <zhangzihuan@...inos.cn>
> >> ---
> >>   drivers/powercap/dtpm_cpu.c | 30 +++++++++++-------------------
> >>   1 file changed, 11 insertions(+), 19 deletions(-)
> >>
> >> diff --git a/drivers/powercap/dtpm_cpu.c b/drivers/powercap/dtpm_cpu.c
> >> index 99390ec1481f..f76594185fa2 100644
> >> --- a/drivers/powercap/dtpm_cpu.c
> >> +++ b/drivers/powercap/dtpm_cpu.c
> >> @@ -144,19 +144,17 @@ static int update_pd_power_uw(struct dtpm *dtpm)
> >>   static void pd_release(struct dtpm *dtpm)
> >>   {
> >>          struct dtpm_cpu *dtpm_cpu = to_dtpm_cpu(dtpm);
> >> -       struct cpufreq_policy *policy;
> >>
> >>          if (freq_qos_request_active(&dtpm_cpu->qos_req))
> >>                  freq_qos_remove_request(&dtpm_cpu->qos_req);
> >>
> >> -       policy = cpufreq_cpu_get(dtpm_cpu->cpu);
> >> -       if (policy) {
> >> +       struct cpufreq_policy *policy __free(put_cpufreq_policy) =
> >> +               cpufreq_cpu_get(dtpm_cpu->cpu);
> >> +
> >> +       if (policy)
> >>                  for_each_cpu(dtpm_cpu->cpu, policy->related_cpus)
> >>                          per_cpu(dtpm_per_cpu, dtpm_cpu->cpu) = NULL;
> >>
> >> -               cpufreq_cpu_put(policy);
> >> -       }
> >> -
> >>          kfree(dtpm_cpu);
> >>   }
> >>
> >> @@ -192,7 +190,6 @@ static int cpuhp_dtpm_cpu_online(unsigned int cpu)
> >>   static int __dtpm_cpu_setup(int cpu, struct dtpm *parent)
> >>   {
> >>          struct dtpm_cpu *dtpm_cpu;
> >> -       struct cpufreq_policy *policy;
> >>          struct em_perf_state *table;
> >>          struct em_perf_domain *pd;
> >>          char name[CPUFREQ_NAME_LEN];
> >> @@ -202,21 +199,19 @@ static int __dtpm_cpu_setup(int cpu, struct dtpm *parent)
> >>          if (dtpm_cpu)
> >>                  return 0;
> >>
> >> -       policy = cpufreq_cpu_get(cpu);
> >> +       struct cpufreq_policy *policy __free(put_cpufreq_policy) =
> >> +               cpufreq_cpu_get(cpu);
> >> +
> >>          if (!policy)
> >>                  return 0;
> >>
> >>          pd = em_cpu_get(cpu);
> >> -       if (!pd || em_is_artificial(pd)) {
> >> -               ret = -EINVAL;
> >> -               goto release_policy;
> >> -       }
> >> +       if (!pd || em_is_artificial(pd))
> >> +               return -EINVAL;
> >>
> >>          dtpm_cpu = kzalloc(sizeof(*dtpm_cpu), GFP_KERNEL);
> >> -       if (!dtpm_cpu) {
> >> -               ret = -ENOMEM;
> >> -               goto release_policy;
> >> -       }
> >> +       if (!dtpm_cpu)
> >> +               return -ENOMEM;
> >>
> >>          dtpm_init(&dtpm_cpu->dtpm, &dtpm_ops);
> >>          dtpm_cpu->cpu = cpu;
> >> @@ -239,7 +234,6 @@ static int __dtpm_cpu_setup(int cpu, struct dtpm *parent)
> >>          if (ret < 0)
> >>                  goto out_dtpm_unregister;
> > So this change kind of goes against another recommendation given in cleanup.h:
> >
> >   * Lastly, given that the benefit of cleanup helpers is removal of
> >   * "goto", and that the "goto" statement can jump between scopes, the
> >   * expectation is that usage of "goto" and cleanup helpers is never
> >   * mixed in the same function. I.e. for a given routine, convert all
> >   * resources that need a "goto" cleanup to scope-based cleanup, or
> >   * convert none of them.
>
>
> Should I replace all the memory allocation cleanups here with `__free`?
> That would allow us to drop all the `goto`s, but since this function has
> quite a few of them, I’m concerned it might introduce new issues. What’s
> your recommendation?

Frankly, don't use __free() in this code at all, at least for the time being.

There is a problem with dropping the reference to policy at the end of
__dtpm_cpu_setup() because that policy may be subsequently indirectly
used in set_pd_power_limit() which calls
freq_qos_update_request(&dtpm_cpu->qos_req, freq) and
dtpm_cpu->qos_req->qos is policy->constraints, so using it will cause
policy->constraints to be dereferenced in freq_qos_apply() which will
crash and burn if the policy goes away in the meantime.  So AFAICS
__dtpm_cpu_setup() shouldn't call cpufreq_cpu_put() at all and the
policy should be released in pd_release() without acquiring a new
reference to it.

You may as well try to fix this if you have free cycles.

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