Re: [RFC PATCH 1/7] drivers: base: Add resource managed version of delayed work init

["gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>]

On Mon, Feb 15, 2021 at 11:37:26AM +0100, Hans de Goede wrote:
> Hi,
> 
> On 2/15/21 8:22 AM, Vaittinen, Matti wrote:
> > 
> > On Sat, 2021-02-13 at 16:59 +0100, Hans de Goede wrote:
> >> Hi,
> >>
> >> On 2/13/21 4:27 PM, Guenter Roeck wrote:
> >>> On 2/13/21 7:03 AM, Hans de Goede wrote:
> >>> [ ... ]
> >>>> I think something like this should work:
> >>>>
> >>>> static int devm_delayed_work_autocancel(struct device *dev,
> >>>> struct delayed_work *w,
> >>>> 					void (*worker)(struct
> >>>> work_struct *work)) {
> >>>> 	INIT_DELAYED_WORK(w, worker);
> >>>> 	return devm_add_action(dev, (void (*action)(void
> >>>> *))cancel_delayed_work_sync, w);
> >>>> }
> >>>>
> >>>> I'm not sure about the cast, that may need something like this
> >>>> instead:
> >>>>
> >>>> typedef void (*devm_action_func)(void *);
> >>>>
> >>>> static int devm_delayed_work_autocancel(struct device *dev,
> >>>> struct delayed_work *w,
> >>>> 					void (*worker)(struct
> >>>> work_struct *work)) {
> >>>> 	INIT_DELAYED_WORK(w, worker);
> >>>> 	return devm_add_action(dev,
> >>>> (devm_action_func)cancel_delayed_work_sync, w);
> >>>
> >>> Unfortunately, you can not type cast function pointers in C. It is
> >>> against the C ABI.
> >>> I am sure it is done in a few places in the kernel anyway, but
> >>> those are wrong.
> >>
> >> I see, bummer.
> > 
> > I think using devm_add_action() is still a good idea.
> 
> Yes, we could also just have a 1 line static inline function to do
> the function-cast. Like this:
> 
> static inline void devm_delayed_work_autocancel_func(void *work)
> {
> 	cancel_delayed_work_sync(work);
> }
> 
> static inline int devm_delayed_work_autocancel(struct device *dev, struct delayed_work *w, void (*worker)(struct work_struct *work))
> {
> 	INIT_DELAYED_WORK(w, worker);
> 	return devm_add_action(dev, devm_delayed_work_autocancel_func, w);
> }
> 
> Both functions will then simply be compiled out in files which do not
> use them.
> 
> >> If we add a devm_clk_prepare_enable() helper that should probably be
> >> added
> >> to drivers/clk/clk-devres.c and not to drivers/base/devres.c .
> >>
> >> I also still wonder if we cannot find a better place for this new
> >> devm_delayed_work_autocancel() helper but nothing comes to mind.
> > 
> > I don't like the idea of including device.h from workqueue.h - and I
> > think this would be necessary if we added
> > devm_delayed_work_autocancel() as inline in workqueue.h, right?
> 
> Yes.
> 
> > I also see strong objection towards the devm managed clean-ups.
> 
> Yes it seems that there are some people who don't like this, where as
> others do like them.
> 
> > How about adding some devm-helpers.c in drivers/base - where we could
> > collect devm-based helpers - and which could be enabled by own CONFIG -
> > and left out by those who dislike it?
> 
> I would make this something configurable through Kconfig, but if
> go the static inline route, which I'm in favor of then we could just
> have a:
> 
> include/linux/devm-cleanup-helpers.h
> 
> And put everything (including kdoc texts) there.
> 
> This way the functionality is 100% opt-in (by explicitly including
> the header if you want the helpers) which hopefully makes this a
> bit more acceptable to people who don't like this style of cleanups.
> 
> I would be even happy to act as the upstream maintainer for such a
> include/linux/devm-cleanup-helpers.h file, I can maintain it as part
> of the platform-drivers-x86 tree (with its own MAINTAINERS entry).
> 
> Greg, would this be an acceptable solution to you ?

I don't know, sorry, let's revisit this after 5.12-rc1 is out, with a
patch set that I can review again, and we can go from there as I can't
do anything until then...

thanks,

greg k-h