Re: [PATCH] cpufreq: unlock when failing cpufreq_update_policy()

[Aaron Plattner]

On 06/18/2014 12:40 AM, Viresh Kumar wrote:
> On 18 June 2014 05:42, Aaron Plattner <aplattner@xxxxxxxxxx> 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@xxxxxxxxxx>
> > Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > Signed-off-by: Aaron Plattner <aplattner@xxxxxxxxxx>
> > ---
> > 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;

I assume you meant "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:

'no_policy' implied to me that policy was NULL, so this label should 
still be renamed to 'unlock'.  I'll send out a v2 that does this.

>          up_write(&policy->rwsem);
>
>          cpufreq_cpu_put(policy);
> -no_policy:
>          return ret;
>   }
>   EXPORT_SYMBOL(cpufreq_update_policy);

--
Aaron
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