linux-kernel - Re: [v1 2/3] include: move lookup_or_create_module_kobject()/to

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Message-ID: <20250207054325.GA25299@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date: Thu, 6 Feb 2025 21:43:25 -0800
From: Shyam Saini <shyamsaini@...ux.microsoft.com>
To: Rasmus Villemoes <linux@...musvillemoes.dk>, hch@...radead.org,
	christophe.leroy@...roup.eu
Cc: linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org,
	code@...icks.com, mcgrof@...nel.org, frkaya@...ux.microsoft.com,
	vijayb@...ux.microsoft.com, petr.pavlu@...e.com,
	linux@...ssschuh.net, samitolvanen@...gle.com, da.gomez@...sung.com,
	gregkh@...uxfoundation.org, rafael@...nel.org, dakr@...nel.org
Subject: Re: [v1 2/3] include: move
 lookup_or_create_module_kobject()/to_module* to module.h

Hi Everyone,

On Wed, Feb 05, 2025 at 09:43:12AM +0100, Rasmus Villemoes wrote:
> On Mon, Feb 03 2025, Shyam Saini <shyamsaini@...ux.microsoft.com> wrote:
> 
> > Move the following to module.h to allow common usages:
> >  - lookup_or_create_module_kobject()
> >  - to_module_attr
> >  - to_module_kobject
> >
> > This makes lookup_or_create_module_kobject() as inline.
> >
> > Signed-off-by: Shyam Saini <shyamsaini@...ux.microsoft.com>
> > ---
> >  include/linux/module.h | 39 +++++++++++++++++++++++++++++++++++++++
> >  kernel/params.c        | 39 ---------------------------------------
> >  2 files changed, 39 insertions(+), 39 deletions(-)
> >
> > diff --git a/include/linux/module.h b/include/linux/module.h
> > index 12f8a7d4fc1c..ba5f5e6c3927 100644
> > --- a/include/linux/module.h
> > +++ b/include/linux/module.h
> > @@ -894,8 +894,47 @@ static inline void *module_writable_address(struct module *mod, void *loc)
> >  #endif /* CONFIG_MODULES */
> >  
> >  #ifdef CONFIG_SYSFS
> > +/* sysfs output in /sys/modules/XYZ/parameters/ */
> > +#define to_module_attr(n) container_of_const(n, struct module_attribute, attr)
> > +#define to_module_kobject(n) container_of(n, struct module_kobject, kobj)
> >  extern struct kset *module_kset;
> >  extern const struct kobj_type module_ktype;
> > +
> > +static inline struct module_kobject * __init lookup_or_create_module_kobject(const char *name)
> 
> As others have said, this is way too big for an inline. Also, __init is
> at best harmless (if it is indeed inlined into all callers), but if for
> whatever reason the compiler decides to emit an OOL version, we
> definitely do not want that in .init.text as we are now calling it from
> non-init code.
> 
> > +{
> > +	struct module_kobject *mk;
> > +	struct kobject *kobj;
> > +	int err;
> > +
> > +	kobj = kset_find_obj(module_kset, name);
> > +	if (kobj) {
> > +		mk = to_module_kobject(kobj);
> > +	} else {
> > +		mk = kzalloc(sizeof(struct module_kobject), GFP_KERNEL);
> > +		BUG_ON(!mk);
> > +
> 
> And while the BUG_ON() is borderline acceptable in the current,
> only-used-during-init, state, that definitely must go away once the
> function can be called from non-init code.
> 
> This is what I alluded to when I said that the function might need some
> refactoring before module_add_driver can start using it.
> 
> I'd say that the BUG_ON can simply be removed and replaced by a return
> NULL; an "impossible" error case that can already be hit by some of the
> code below, so callers have to be prepared for it anyway. If the
> allocation fails (during early boot or later), the allocator already
> makes a lot of noise, so there's no reason to even do a WARN_ON, and
> since it "only" affects certain /sys objects, it's probably better to
> let the machine try to complete boot instead of killing it.
> 
> Also, I agree with the suggestion to drop/outdent the whole else{} branch by
> changing the if() to do "return to_module_kobject(kobj);".
> 
> To summarize:
> 
> - refactor to do an early return
> 
> - drop BUG_ON, replace by return NULL.
> 
> - drop static and __init, perhaps change __init to __modinit (which is a
>   pre-existing #define in params.c, so the function remains __init if
>   !CONFIG_MODULES), add an appropriate declaration somewhere, and if you
>   like, also do the rename
> 
> - make use of it from module_add_driver()

I have addressed these feedback in v2, thank you for the reviews.

Thanks,
Shyam