Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Mon, 29 Jun 2020 15:13:46 +0200 | Subject | Re: [PATCH V3 1/3] cpufreq: Fix locking issues with governors |
| |
On Mon, Jun 29, 2020 at 4:13 AM Viresh Kumar <viresh.kumar@linaro.org> wrote: > > On 26-06-20, 09:24, Quentin Perret wrote: > > 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). > > I described why I chose to keep it that way in the other email, but I > am all for dropping the variable. And so what about this ?
Works for me.
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index e798a1193bdf..d9e9ae7051bb 100644 > --- a/drivers/cpufreq/cpufreq.c > +++ b/drivers/cpufreq/cpufreq.c > @@ -1064,18 +1064,17 @@ 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 = 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) { > gov = def_gov; > + module_get(gov->owner); > } else { > return -ENODATA; > } > @@ -1099,7 +1098,7 @@ static int cpufreq_init_policy(struct cpufreq_policy *policy) > } > > ret = cpufreq_set_policy(policy, gov, pol); > - if (put_governor) > + if (gov) > module_put(gov->owner); > > return ret; > > -- > viresh
| |