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SubjectRe: [PATCH] cpufreq: Make cpufreq_online() call driver->offline() on errors
On 21-06-21, 19:26, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> In the CPU removal path the ->offline() callback provided by the
> driver is always invoked before ->exit(),

Note that exit() doesn't get called if offline() is present in the CPU
removal path. We call exit() _only_ when the cpufreq driver gets
unregistered.

> but in the cpufreq_online()
> error path it is not, so ->exit() is somehow expected to know the
> context in which it has been called and act accordingly.

I agree, it isn't very clear.

> That is less than straightforward, so make cpufreq_online() invoke
> the driver's ->offline() callback before ->exit() too.
>
> This only potentially affects intel_pstate at this point.
>
> Fixes: 91a12e91dc39 ("cpufreq: Allow light-weight tear down and bring up of CPUs")
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> drivers/cpufreq/cpufreq.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> Index: linux-pm/drivers/cpufreq/cpufreq.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/cpufreq.c
> +++ linux-pm/drivers/cpufreq/cpufreq.c
> @@ -1516,6 +1516,9 @@ out_destroy_policy:
> up_write(&policy->rwsem);
>
> out_exit_policy:
> + if (cpufreq_driver->offline)
> + cpufreq_driver->offline(policy);
> +
> if (cpufreq_driver->exit)
> cpufreq_driver->exit(policy);

If we want to go down this path, then we better do more and make it
very explicit that ->offline() follows a previous invocation of
->online().

Otherwise, with above we will end up calling ->offline() for two separate
states, ->online() failed (i.e. two calls to offline() one after the other
here) and other generic failures after ->init() passed.

So, better make it clear that online/offline are paired like
init/exit.

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 1d1b563cea4b..0ce48dcb2e8a 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1347,14 +1347,11 @@ static int cpufreq_online(unsigned int cpu)
}

if (!new_policy && cpufreq_driver->online) {
- ret = cpufreq_driver->online(policy);
- if (ret) {
- pr_debug("%s: %d: initialization failed\n", __func__,
- __LINE__);
- goto out_exit_policy;
- }
-
- /* Recover policy->cpus using related_cpus */
+ /*
+ * We did light-weight tear down earlier, don't need to do heavy
+ * initialization here. Just recover policy->cpus using
+ * related_cpus.
+ */
cpumask_copy(policy->cpus, policy->related_cpus);
} else {
cpumask_copy(policy->cpus, cpumask_of(cpu));
@@ -1378,6 +1375,13 @@ static int cpufreq_online(unsigned int cpu)
cpumask_copy(policy->related_cpus, policy->cpus);
}

+ ret = cpufreq_driver->online(policy);
+ if (ret) {
+ pr_debug("%s: %d: %d: ->online() failed\n", __func__, __LINE__,
+ ret);
+ goto out_exit_policy;
+ }
+
down_write(&policy->rwsem);
/*
* affected cpus must always be the one, which are online. We aren't
@@ -1518,6 +1522,9 @@ static int cpufreq_online(unsigned int cpu)

up_write(&policy->rwsem);

+ if (cpufreq_driver->offline)
+ cpufreq_driver->offline(policy);
+
out_exit_policy:
if (cpufreq_driver->exit)
cpufreq_driver->exit(policy);

--
viresh

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