netdev - Re: [PATCH v3 1/2] PM: runtime: Add pm_runtime_resume_and

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Date:   Mon, 30 Nov 2020 17:37:52 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Zhang Qilong <zhangqilong3@...wei.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Fugang Duan <fugang.duan@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH v3 1/2] PM: runtime: Add pm_runtime_resume_and_get to deal
 with usage counter

On Fri, Nov 27, 2020 at 11:16 AM Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
>
> Hi Zhang,
>
> On Tue, Nov 10, 2020 at 10:29 AM Zhang Qilong <zhangqilong3@...wei.com> wrote:
> > In many case, we need to check return value of pm_runtime_get_sync, but
> > it brings a trouble to the usage counter processing. Many callers forget
> > to decrease the usage counter when it failed, which could resulted in
> > reference leak. It has been discussed a lot[0][1]. So we add a function
> > to deal with the usage counter for better coding.
> >
> > [0]https://lkml.org/lkml/2020/6/14/88
> > [1]https://patchwork.ozlabs.org/project/linux-tegra/list/?series=178139
> > Signed-off-by: Zhang Qilong <zhangqilong3@...wei.com>
>
> Thanks for your patch, which is now commit dd8088d5a8969dc2 ("PM:
> runtime: Add pm_runtime_resume_and_get to deal with usage counter") in
> v5.10-rc5.
>
> > --- a/include/linux/pm_runtime.h
> > +++ b/include/linux/pm_runtime.h
> > @@ -386,6 +386,27 @@ static inline int pm_runtime_get_sync(struct device *dev)
> >         return __pm_runtime_resume(dev, RPM_GET_PUT);
> >  }
> >
> > +/**
> > + * pm_runtime_resume_and_get - Bump up usage counter of a device and resume it.
> > + * @dev: Target device.
> > + *
> > + * Resume @dev synchronously and if that is successful, increment its runtime
> > + * PM usage counter. Return 0 if the runtime PM usage counter of @dev has been
> > + * incremented or a negative error code otherwise.
> > + */
> > +static inline int pm_runtime_resume_and_get(struct device *dev)
>
> Perhaps this function should be called pm_runtime_resume_and_get_sync(),

No, really.

I might consider calling it pm_runtime_acquire(), and adding a
matching _release() as a pm_runtime_get() synonym for that matter, but
not the above.

> to make it clear it does a synchronous get?
>
> I had to look into the implementation to verify that a change like

I'm not sure why, because the kerneldoc is unambiguous AFAICS.

>
> -       ret = pm_runtime_get_sync(&pdev->dev);
> +       ret = pm_runtime_resume_and_get(&pdev->dev);
>
> in the follow-up patches is actually a valid change, maintaining
> synchronous operation. Oh, pm_runtime_resume() is synchronous, too...

Yes, it is.