From: Quentin Perret <qperret@google.com>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Rafael Wysocki <rjw@rjwysocki.net>,
linux-pm@vger.kernel.org,
Vincent Guittot <vincent.guittot@linaro.org>,
kernel-team@android.com, tkjos@google.com,
adharmap@codeaurora.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH V3 1/3] cpufreq: Fix locking issues with governors
Date: Fri, 26 Jun 2020 09:24:33 +0100 [thread overview]
Message-ID: <20200626082433.GA284605@google.com> (raw)
In-Reply-To: <f366ed3dd3dd111e42173b366fe4dd5a0e4647fd.1593143118.git.viresh.kumar@linaro.org>
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!
next prev parent reply other threads:[~2020-06-26 8:24 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-26 3:51 [PATCH v3 0/3] cpufreq: Allow default governor on cmdline and fix locking issues Viresh Kumar
2020-06-26 3:51 ` [PATCH V3 1/3] cpufreq: Fix locking issues with governors Viresh Kumar
2020-06-26 8:24 ` Quentin Perret [this message]
2020-06-29 2:13 ` Viresh Kumar
2020-06-29 8:05 ` Quentin Perret
2020-06-29 13:13 ` Rafael J. Wysocki
2020-06-26 3:51 ` [PATCH V3 2/3] cpufreq: Register governors at core_initcall Viresh Kumar
2020-06-26 3:51 ` [PATCH V3 3/3] cpufreq: Specify default governor on command line Viresh Kumar
2020-06-26 15:57 ` Quentin Perret
2020-06-29 2:08 ` Viresh Kumar
2020-06-29 8:03 ` Quentin Perret
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200626082433.GA284605@google.com \
--to=qperret@google.com \
--cc=adharmap@codeaurora.org \
--cc=kernel-team@android.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pm@vger.kernel.org \
--cc=rjw@rjwysocki.net \
--cc=tkjos@google.com \
--cc=vincent.guittot@linaro.org \
--cc=viresh.kumar@linaro.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).