linux-kernel - Re: [PATCH v2] params: Add support for static keys

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Message-ID: <tjqz5spozvd35egxtfn2n3csvqu2qsaobbkfzf52ovhsokq47y@eq5xl2ugyydq>
Date: Tue, 13 May 2025 19:34:59 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: linux-kernel@...r.kernel.org, Luis Chamberlain <mcgrof@...nel.org>, 
	Petr Pavlu <petr.pavlu@...e.com>, Sami Tolvanen <samitolvanen@...gle.com>, 
	Daniel Gomez <da.gomez@...sung.com>, linux-modules@...r.kernel.org, 
	Peter Zijlstra <peterz@...radead.org>, Jason Baron <jbaron@...mai.com>, 
	Steven Rostedt <rostedt@...dmis.org>, Ard Biesheuvel <ardb@...nel.org>
Subject: Re: [PATCH v2] params: Add support for static keys

On Tue, May 13, 2025 at 02:24:46PM -0700, Josh Poimboeuf wrote:
> On Tue, May 13, 2025 at 09:07:32AM -0400, Kent Overstreet wrote:
> > Static keys can now be a module parameter, e.g.
> > 
> > module_param_named(foo, foo.key, static_key_t, 0644)
> > 
> > bcachefs is now using this.
> > 
> > Cc: Luis Chamberlain <mcgrof@...nel.org>
> > Cc: Petr Pavlu <petr.pavlu@...e.com>
> > Cc: Sami Tolvanen <samitolvanen@...gle.com>
> > Cc: Daniel Gomez <da.gomez@...sung.com>
> > Cc: linux-modules@...r.kernel.org
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Josh Poimboeuf <jpoimboe@...nel.org>
> > Cc: Jason Baron <jbaron@...mai.com>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Ard Biesheuvel <ardb@...nel.org>
> > Signed-off-by: Kent Overstreet <kent.overstreet@...ux.dev>
> > ---
> >  include/linux/jump_label.h  |  2 ++
> >  include/linux/moduleparam.h |  7 +++++++
> >  kernel/params.c             | 35 +++++++++++++++++++++++++++++++++++
> >  3 files changed, 44 insertions(+)
> > 
> > diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
> > index fdb79dd1ebd8..0fc9b71db56f 100644
> > --- a/include/linux/jump_label.h
> > +++ b/include/linux/jump_label.h
> > @@ -107,6 +107,8 @@ struct static_key {
> >  #endif	/* CONFIG_JUMP_LABEL */
> >  };
> >  
> > +typedef struct static_key static_key_t;
> > +
> >  #endif /* __ASSEMBLY__ */
> >  
> >  #ifdef CONFIG_JUMP_LABEL
> > diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
> > index bfb85fd13e1f..11e8d5c57435 100644
> > --- a/include/linux/moduleparam.h
> > +++ b/include/linux/moduleparam.h
> > @@ -122,6 +122,7 @@ struct kparam_array
> >   *	charp: a character pointer
> >   *	bool: a bool, values 0/1, y/n, Y/N.
> >   *	invbool: the above, only sense-reversed (N = true).
> > + *	static_key_t: same as bool, but updates a 'struct static_key'
> 
> The static_key_*() interfaces are deprecated because they're really easy
> to use incorrectly.  I don't think we want to propagate that misuse to
> modules.
> 
> It would be better to have type(s) based on static_key_false and/or
> static_key_true, depending on whatever the default is.

Except those are just wrappers around struct static_key, so why does
that matter here?