linux-kernel - Re: [PATCH RFC] kprobes: Remove MODULES dependency

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Date:   Fri, 10 Jul 2020 08:51:56 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Will Deacon <will@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Alexandre Ghiti <alex@...ti.fr>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH RFC] kprobes: Remove MODULES dependency

On Fri, Jul 10, 2020 at 07:32:57PM +0900, Masami Hiramatsu wrote:
> On Fri, 10 Jul 2020 02:45:19 +0300
> Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com> wrote:
> > +#ifdef CONFIG_MODULES
> >  	/* Lock modules while optimizing kprobes */
> >  	mutex_lock(&module_mutex);
> > +#endif
> 
> Hmm, can you reduce these "#ifdef CONFIG_MODULE"s ?
> 
> e.g. 
> 
> #ifdef CONFIG_MODULES
> static void lock_modules(void)
> {
> 	mutex_lock(&module_mutex);
> }
> ...
> #else
> #define lock_modules() do { } while (0)
> ...
> #endif

I prefer using "static inline" for no-op functions just because they
will maintain argument type validation by the compiler regardless of the
CONFIG state (though it doesn't really matter here since it's void).

#else
static inline lock_modules(void) { }
#endif

-- 
Kees Cook