linux-kernel - Re: [PATCH] cpufreq: unlock when failing cpufreq_update

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Message-ID: <CAKohpo=2fpi7GivgNGE+DgD3xPdku3WzKKD8+Ziz4gQ4P6pMxQ@mail.gmail.com>
Date:	Wed, 18 Jun 2014 13:10:40 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Aaron Plattner <aplattner@...dia.com>
Cc:	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH] cpufreq: unlock when failing cpufreq_update_policy()

On 18 June 2014 05:42, Aaron Plattner <aplattner@...dia.com> wrote:
> Commit bd0fa9bb455d introduced a failure path to cpufreq_update_policy() if
> cpufreq_driver->get(cpu) returns NULL.  However, it jumps to the 'no_policy'
> label, which exits without unlocking any of the locks the function acquired
> earlier.  This causes later calls into cpufreq to hang.
>
> Fix this by creating a new 'unlock' label and jumping to that instead.
>
> Fixes: bd0fa9bb455d ("cpufreq: Return error if ->get() failed in cpufreq_update_policy()")
> Link: https://devtalk.nvidia.com/default/topic/751903/kernel-3-15-and-nv-drivers-337-340-failed-to-initialize-the-nvidia-kernel-module-gtx-550-ti-/
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Signed-off-by: Aaron Plattner <aplattner@...dia.com>
> ---
> I haven't reproduced this problem so I couldn't test it, but the bug and its
> solution seem obvious enough.
>
>  drivers/cpufreq/cpufreq.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index aed2b0cb83dc..5b6d04f3b9ea 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2264,7 +2264,7 @@ int cpufreq_update_policy(unsigned int cpu)
>                 new_policy.cur = cpufreq_driver->get(cpu);
>                 if (WARN_ON(!new_policy.cur)) {
>                         ret = -EIO;
> -                       goto no_policy;
> +                       goto unlock;
>                 }
>
>                 if (!policy->cur) {
> @@ -2279,6 +2279,7 @@ int cpufreq_update_policy(unsigned int cpu)
>
>         ret = cpufreq_set_policy(policy, &new_policy);
>
> +unlock:
>         up_write(&policy->rwsem);
>
>         cpufreq_cpu_put(policy);

Hmm, yes we do have a problem here but the code became a bit ugly
now.. Can you please consider this diff instead?

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index aed2b0c..6caced5 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -2242,10 +2242,8 @@ int cpufreq_update_policy(unsigned int cpu)
        struct cpufreq_policy new_policy;
        int ret;

-       if (!policy) {
-               ret = -ENODEV;
-               goto no_policy;
-       }
+       if (!policy)
+               return = -ENODEV;

        down_write(&policy->rwsem);

@@ -2279,10 +2277,10 @@ int cpufreq_update_policy(unsigned int cpu)

        ret = cpufreq_set_policy(policy, &new_policy);

+no_policy:
        up_write(&policy->rwsem);

        cpufreq_cpu_put(policy);
-no_policy:
        return ret;
 }
 EXPORT_SYMBOL(cpufreq_update_policy);
--
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