Messages in this thread | | | Date | Fri, 26 Jun 2020 09:24:33 +0100 | From | Quentin Perret <> | Subject | Re: [PATCH V3 1/3] cpufreq: Fix locking issues with governors |
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On Friday 26 Jun 2020 at 09:21:42 (+0530), Viresh Kumar wrote: > The locking around governors handling isn't adequate currently. The list > of governors should never be traversed without locking in place. Also we > must make sure the governor isn't removed while it is still referenced > by code. > > Reported-by: Quentin Perret <qperret@google.com> > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> > --- > drivers/cpufreq/cpufreq.c | 59 ++++++++++++++++++++++++--------------- > 1 file changed, 36 insertions(+), 23 deletions(-) > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index 0128de3603df..e798a1193bdf 100644 > --- a/drivers/cpufreq/cpufreq.c > +++ b/drivers/cpufreq/cpufreq.c > @@ -621,6 +621,24 @@ static struct cpufreq_governor *find_governor(const char *str_governor) > return NULL; > } > > +static struct cpufreq_governor *get_governor(const char *str_governor) > +{ > + struct cpufreq_governor *t; > + > + mutex_lock(&cpufreq_governor_mutex); > + t = find_governor(str_governor); > + if (!t) > + goto unlock; > + > + if (!try_module_get(t->owner)) > + t = NULL; > + > +unlock: > + mutex_unlock(&cpufreq_governor_mutex); > + > + return t; > +} > + > static unsigned int cpufreq_parse_policy(char *str_governor) > { > if (!strncasecmp(str_governor, "performance", CPUFREQ_NAME_LEN)) > @@ -640,28 +658,14 @@ static struct cpufreq_governor *cpufreq_parse_governor(char *str_governor) > { > struct cpufreq_governor *t; > > - mutex_lock(&cpufreq_governor_mutex); > - > - t = find_governor(str_governor); > - if (!t) { > - int ret; > - > - mutex_unlock(&cpufreq_governor_mutex); > - > - ret = request_module("cpufreq_%s", str_governor); > - if (ret) > - return NULL; > - > - mutex_lock(&cpufreq_governor_mutex); > + t = get_governor(str_governor); > + if (t) > + return t; > > - t = find_governor(str_governor); > - } > - if (t && !try_module_get(t->owner)) > - t = NULL; > - > - mutex_unlock(&cpufreq_governor_mutex); > + if (request_module("cpufreq_%s", str_governor)) > + return NULL; > > - return t; > + return get_governor(str_governor); > } > > /** > @@ -815,12 +819,14 @@ static ssize_t show_scaling_available_governors(struct cpufreq_policy *policy, > goto out; > } > > + mutex_lock(&cpufreq_governor_mutex); > for_each_governor(t) { > if (i >= (ssize_t) ((PAGE_SIZE / sizeof(char)) > - (CPUFREQ_NAME_LEN + 2))) > - goto out; > + break; > i += scnprintf(&buf[i], CPUFREQ_NAME_PLEN, "%s ", t->name); > } > + mutex_unlock(&cpufreq_governor_mutex); > out: > i += sprintf(&buf[i], "\n"); > return i; > @@ -1058,11 +1064,14 @@ static int cpufreq_init_policy(struct cpufreq_policy *policy) > struct cpufreq_governor *def_gov = cpufreq_default_governor(); > struct cpufreq_governor *gov = NULL; > unsigned int pol = CPUFREQ_POLICY_UNKNOWN; > + bool put_governor = false; > + int ret; > > if (has_target()) { > /* Update policy governor to the one used before hotplug. */ > - gov = find_governor(policy->last_governor); > + gov = get_governor(policy->last_governor); > if (gov) { > + put_governor = true; > pr_debug("Restoring governor %s for cpu %d\n", > policy->governor->name, policy->cpu); > } else if (def_gov) { > @@ -1089,7 +1098,11 @@ static int cpufreq_init_policy(struct cpufreq_policy *policy) > return -ENODATA; > } > > - return cpufreq_set_policy(policy, gov, pol); > + ret = cpufreq_set_policy(policy, gov, pol); > + if (put_governor) > + module_put(gov->owner);
Nit: I think you could safely do
if (gov) module_put(gov->owner);
and get rid of 'put_governor', given that try_module_get() and module_put() are nops if owner is NULL (which is guaranteed for the result of cpufreq_default_governor() as it is builtin).
But other than that:
Reviewed-by: Quentin Perret <qperret@google.com>
Thanks!
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