linux-kernel - Re: PM runtime auto-cleanup macros

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Message-ID: <CAJZ5v0jafoG--WrZNjt+euY0gtQSTqSDH2_cWotf92ziq5wdUw@mail.gmail.com>
Date: Thu, 18 Sep 2025 22:19:23 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Takashi Iwai <tiwai@...e.de>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: PM runtime auto-cleanup macros

On Thu, Sep 18, 2025 at 1:28 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Thu, Sep 18, 2025 at 9:10 AM Takashi Iwai <tiwai@...e.de> wrote:
> >
> > On Wed, 17 Sep 2025 20:58:36 +0200,
> > Rafael J. Wysocki wrote:
> > >
> > > Hi,
> > >
> > > Sorry for the delay.
> > >
> > > On Thu, Sep 11, 2025 at 9:31 AM Takashi Iwai <tiwai@...e.de> wrote:
> > > >
> > > > On Wed, 10 Sep 2025 16:00:17 +0200,
> > > > Takashi Iwai wrote:
> > > > >
> > > > > Hi,
> > > > >
> > > > > while I worked on the code cleanups in the drivers with the recent
> > > > > auto-cleanup macros, I noticed that pm_runtime_get*() and _put*() can
> > > > > be also managed with the auto-cleanup gracefully, too.  Actually we
> > > > > already defined the __free(pm_runtime_put) in commit bfa4477751e9, and
> > > > > there is a (single) user of it in pci-sysfs.c.
> > > > >
> > > > > Now I wanted to extend it to pm_runtime_put_autosuspend() as:
> > > > >
> > > > > DEFINE_FREE(pm_runtime_put_autosuspend, struct device *,
> > > > >            if (_T) pm_runtime_put_autosuspend(_T))
> > > > >
> > > > > Then one can use it like
> > > > >
> > > > >       ret = pm_runtime_resume_and_get(dev);
> > > > >       if (ret < 0)
> > > > >               return ret;
> > > > >       struct device *pmdev __free(pm_runtime_put_autosuspend) = dev;
> > > > >
> > > > > that is similar as done in pci-sysfs.c.  So far, so good.
> > > > >
> > > > > But, I find putting the line like above at each place a bit ugly.
> > > > > So I'm wondering whether it'd be better to introduce some helper
> > > > > macros, e.g.
> > > > >
> > > > > #define pm_runtime_auto_clean(dev, var) \
> > > > >       struct device *var __free(pm_runtime_put) = (dev)
> > > >
> > > > It can be even simpler by assigning a temporary variable such as:
> > > >
> > > > #define pm_runtime_auto_clean(dev) \
> > > >         struct device *__pm_runtime_var ## __LINE__ __free(pm_runtime_put) = (dev)
> > >
> > > Well, if there's something like
> > >
> > > struct device *pm_runtime_resume_and_get_dev(struct device *dev)
> > > {
> > >         int ret = pm_runtime_resume_and_get(dev);
> > >         if (ret < 0)
> > >                 return ERR_PTR(ret);
> > >
> > >         return dev;
> > > }
> > >
> > > It would be a matter of redefining the FREE to also take error
> > > pointers into account and you could do
> > >
> > > struct device *__dev __free(pm_runtim_put) = pm_runtime_resume_and_get_dev(dev);
> > > if (IS_ERR(__dev))
> > >         return PTR_ERR(__dev);
> >
> > That'll work, too.  Though, I find the notion of __free() and a
> > temporary variable __dev a bit too cumbersome; it's used only for
> > auto-clean stuff, so it could be somewhat anonymous.
>
> No, it is not used only for auto-clean, it is also used for return
> value checking and it represents a reference on the original dev.  It
> cannot be entirely anonymous because of the error checking part.
>
> The point is that this is one statement instead of two and so it is
> arguably harder to mess up with.
>
> > But it's all about a matter of taste, and I'd follow what you and
> > other guys suggest.
> >
> > FWIW, there are lots of code doing like
> >
> >         pm_runtime_get_sync(dev);
> >         mutex_lock(&foo);
> >         ....
> >         mutex_unlock(&foo);
> >         pm_runtime_put(dev);
> >         return;
> >
> > or
> >
> >         ret = pm_runtime_resume_and_get(dev);
> >         if (ret)
> >                 return ret;
> >         mutex_lock(&foo);
> >         ....
> >         mutex_unlock(&foo);
> >         pm_runtime_put_autosuspend(dev);
> >         return 0;
> >
> > and they can be converted nicely with guard() once when PM runtime can
> > be automatically unreferenced.  With my proposed change, it would
> > become like:
> >
> >         pm_runtime_get_sync(dev);
> >         pm_runtime_auto_clean(dev);
>
> For the case in which the pm_runtime_get_sync() return value is
> discarded, you could define a guard and do
>
> guard(pm_runtime_get_sync)(dev);
>
> here.
>
> The case checking the return value is less straightforward.
>
> >         guard(mutex)(&foo);
> >         ....
> >         return;
> >
> > or
> >
> >         ret = pm_runtime_resume_and_get(dev);
> >         if (ret)
> >                 return ret;
> >         pm_runtime_auto_clean_autosuspend(dev);
> >         guard(mutex)(&foo);
> >         ....
> >         return 0;
> >

I guess what I'm saying means basically something like this:

DEFINE_CLASS(pm_runtime_resume_and_get, struct device *,
         if (!IS_ERR_OR_NULL(_T)) pm_tuntime_put(_T),
pm_runtime_resume_and_get_dev(dev), struct device *dev)

DEFINE_CLASS(pm_runtime_resume_and_get_auto, struct device *,
         if (!IS_ERR_OR_NULL(_T)) pm_tuntime_put_autosuspend(_T),
pm_runtime_resume_and_get_dev(dev), struct device *dev)

and analogously for pm_runtime_get_sync().