linux-kernel - Re: [PATCH 11/15] static_call: Add inline static call infrastructure

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Message-ID: <20190610171929.3xemvsykvkswcvya@treble>
Date:   Mon, 10 Jun 2019 12:19:29 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Nadav Amit <namit@...are.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andy Lutomirski <luto@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jason Baron <jbaron@...mai.com>, Jiri Kosina <jkosina@...e.cz>,
        David Laight <David.Laight@...LAB.COM>,
        Borislav Petkov <bp@...en8.de>,
        Julia Cartwright <julia@...com>, Jessica Yu <jeyu@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Edward Cree <ecree@...arflare.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH 11/15] static_call: Add inline static call infrastructure

On Fri, Jun 07, 2019 at 10:37:56AM +0200, Peter Zijlstra wrote:
> > > +}
> > > +
> > > +static int static_call_module_notify(struct notifier_block *nb,
> > > +				     unsigned long val, void *data)
> > > +{
> > > +	struct module *mod = data;
> > > +	int ret = 0;
> > > +
> > > +	cpus_read_lock();
> > > +	static_call_lock();
> > > +
> > > +	switch (val) {
> > > +	case MODULE_STATE_COMING:
> > > +		module_disable_ro(mod);
> > > +		ret = static_call_add_module(mod);
> > > +		module_enable_ro(mod, false);
> > 
> > Doesn’t it cause some pages to be W+X ?

How so?

>> Can it be avoided?
> 
> I don't know why it does this, jump_labels doesn't seem to need this,
> and I'm not seeing what static_call needs differently.

I forgot why I did this, but it's probably for the case where there's a
static call site in module init code.  It deserves a comment.

Theoretically, jump labels need this to.

BTW, there's a change coming that will require the text_mutex before
calling module_{disable,enable}_ro().

-- 
Josh