linux-kernel - Re: [PATCH v4 14/15] kprobes: remove dependency on CONFIG

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Date: Sat, 20 Apr 2024 18:15:00 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Mike Rapoport <rppt@...nel.org>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
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Subject: Re: [PATCH v4 14/15] kprobes: remove dependency on CONFIG_MODULES

On Sat, 20 Apr 2024 10:33:38 +0300
Mike Rapoport <rppt@...nel.org> wrote:

> On Fri, Apr 19, 2024 at 03:59:40PM +0000, Christophe Leroy wrote:
> > 
> > 
> > Le 19/04/2024 à 17:49, Mike Rapoport a écrit :
> > > Hi Masami,
> > > 
> > > On Thu, Apr 18, 2024 at 06:16:15AM +0900, Masami Hiramatsu wrote:
> > >> Hi Mike,
> > >>
> > >> On Thu, 11 Apr 2024 19:00:50 +0300
> > >> Mike Rapoport <rppt@...nel.org> wrote:
> > >>
> > >>> From: "Mike Rapoport (IBM)" <rppt@...nel.org>
> > >>>
> > >>> kprobes depended on CONFIG_MODULES because it has to allocate memory for
> > >>> code.
> > >>>
> > >>> Since code allocations are now implemented with execmem, kprobes can be
> > >>> enabled in non-modular kernels.
> > >>>
> > >>> Add #ifdef CONFIG_MODULE guards for the code dealing with kprobes inside
> > >>> modules, make CONFIG_KPROBES select CONFIG_EXECMEM and drop the
> > >>> dependency of CONFIG_KPROBES on CONFIG_MODULES.
> > >>
> > >> Thanks for this work, but this conflicts with the latest fix in v6.9-rc4.
> > >> Also, can you use IS_ENABLED(CONFIG_MODULES) instead of #ifdefs in
> > >> function body? We have enough dummy functions for that, so it should
> > >> not make a problem.
> > > 
> > > The code in check_kprobe_address_safe() that gets the module and checks for
> > > __init functions does not compile with IS_ENABLED(CONFIG_MODULES).
> > > I can pull it out to a helper or leave #ifdef in the function body,
> > > whichever you prefer.
> > 
> > As far as I can see, the only problem is MODULE_STATE_COMING.
> > Can we move 'enum module_state' out of #ifdef CONFIG_MODULES in module.h  ?
> 
> There's dereference of 'struct module' there:
>  
> 		(*probed_mod)->state != MODULE_STATE_COMING) {
> 			...
> 		}
> 
> so moving out 'enum module_state' won't be enough.

Hmm, this part should be inline functions like;

#ifdef CONFIG_MODULES
static inline bool module_is_coming(struct module *mod)
{
	return mod->state == MODULE_STATE_COMING;
}
#else
#define module_is_coming(mod) (false)
#endif

Then we don't need the enum.
Thank you,

>  
> > >   
> > >> -- 
> > >> Masami Hiramatsu
> > > 
> 
> -- 
> Sincerely yours,
> Mike.
> 

-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>