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

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Date:   Sat, 13 Feb 2021 12:26:59 +0000
From:   "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
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Subject: Re: [RFC PATCH 1/7] drivers: base: Add resource managed version of
 delayed work init


On Sat, 2021-02-13 at 13:16 +0100, Greg Kroah-Hartman wrote:
> On Sat, Feb 13, 2021 at 01:58:44PM +0200, Matti Vaittinen wrote:
> > A few drivers which need a delayed work-queue must cancel work at
> > exit.
> > Some of those implement remove solely for this purpose. Help
> > drivers
> > to avoid unnecessary remove and error-branch implementation by
> > adding
> > managed verision of delayed work initialization
> > 
> > Signed-off-by: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>
> 
> That's not a good idea.  As this would kick in when the device is
> removed from the system, not when it is unbound from the driver,
> right?
> 
> > ---
> >  drivers/base/devres.c  | 33 +++++++++++++++++++++++++++++++++
> >  include/linux/device.h |  5 +++++
> >  2 files changed, 38 insertions(+)
> > 
> > diff --git a/drivers/base/devres.c b/drivers/base/devres.c
> > index fb9d5289a620..2879595bb5a4 100644
> > --- a/drivers/base/devres.c
> > +++ b/drivers/base/devres.c
> > @@ -1231,3 +1231,36 @@ void devm_free_percpu(struct device *dev,
> > void __percpu *pdata)
> >  			       (void *)pdata));
> >  }
> >  EXPORT_SYMBOL_GPL(devm_free_percpu);
> > +
> > +static void dev_delayed_work_drop(struct device *dev, void *res)
> > +{
> > +	cancel_delayed_work_sync(*(struct delayed_work **)res);
> > +}
> > +
> > +/**
> > + * devm_delayed_work_autocancel - Resource-managed work allocation
> > + * @dev: Device which lifetime work is bound to
> > + * @pdata: work to be cancelled when device exits
> > + *
> > + * Initialize work which is automatically cancelled when device
> > exits.
> 
> There is no such thing in the driver model as "when device exits".
> Please use the proper terminology as I do not understand what you
> think
> this is doing here...
> 
> > + * A few drivers need delayed work which must be cancelled before
> > driver
> > + * is unload to avoid accessing removed resources.
> > + * devm_delayed_work_autocancel() can be used to omit the explicit
> > + * cancelleation when driver is unload.
> > + */
> > +int devm_delayed_work_autocancel(struct device *dev, struct
> > delayed_work *w,
> > +				 void (*worker)(struct work_struct
> > *work))
> > +{
> > +	struct delayed_work **ptr;
> > +
> > +	ptr = devres_alloc(dev_delayed_work_drop, sizeof(*ptr),
> > GFP_KERNEL);
> > +	if (!ptr)
> > +		return -ENOMEM;
> > +
> > +	INIT_DELAYED_WORK(w, worker);
> > +	*ptr = w;
> > +	devres_add(dev, ptr);
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(devm_delayed_work_autocancel);
> > diff --git a/include/linux/device.h b/include/linux/device.h
> > index 1779f90eeb4c..192456198de7 100644
> > --- a/include/linux/device.h
> > +++ b/include/linux/device.h
> > @@ -27,6 +27,7 @@
> >  #include <linux/uidgid.h>
> >  #include <linux/gfp.h>
> >  #include <linux/overflow.h>
> > +#include <linux/workqueue.h>
> >  #include <linux/device/bus.h>
> >  #include <linux/device/class.h>
> >  #include <linux/device/driver.h>
> > @@ -249,6 +250,10 @@ void __iomem *devm_of_iomap(struct device
> > *dev,
> >  			    struct device_node *node, int index,
> >  			    resource_size_t *size);
> >  
> > +/* delayed work which is cancelled when driver exits */
> 
> Not when the "driver exits".
> 
> There is two different lifespans here (well 3).  Code and
> data*2.  Don't
> confuse them as that will just cause lots of problems.
> 
> The move toward more and more "devm" functions is not the way to go
> as
> they just more and more make things easier to get wrong.
> 
> APIs should be impossible to get wrong, this one is going to be
> almost
> impossible to get right.

Thanks for prompt reply. I guess I must've misunderstood some of this
concept. Frankly to say, I don't understand how the devm based irq
management works and this does not. Maybe I'd better study this further
then.

Best Regards
	Matti Vaittinen