Re: [PATCH] cpufreq: Make cpufreq_online() call driver->offline() on errors
From: Viresh Kumar <viresh.kumar@linaro.org>
Date: 2021-06-22 06:20:57
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lkml
Subsystem:
cpu frequency scaling framework, the rest · Maintainers:
"Rafael J. Wysocki", Viresh Kumar, Linus Torvalds
On 21-06-21, 19:26, Rafael J. Wysocki wrote:
From: Rafael J. Wysocki <redacted> 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.
quoted hunk ↗ jump to hunk
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 <redacted> --- 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