Messages in this thread Patch in this message | | | Date | Mon, 29 Jun 2020 07:43:09 +0530 | From | Viresh Kumar <> | Subject | Re: [PATCH V3 1/3] cpufreq: Fix locking issues with governors |
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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 ?
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
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