linux-kernel - Re: [for-next][PATCH 12/16] kprobes: Initialize kprobes at postcore

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Message-Id: <20190709213049.f84b4df6562250ac6ef0b51d@kernel.org>
Date:   Tue, 9 Jul 2019 21:30:49 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Mark Rutland <mark.rutland@....com>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [for-next][PATCH 12/16] kprobes: Initialize kprobes at
 postcore_initcall

Hi Steve,

On Wed, 3 Jul 2019 10:02:05 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Tue, 2 Jul 2019 17:50:09 +0100
> Mark Rutland <mark.rutland@....com> wrote:
> 
> > On Sun, May 26, 2019 at 03:18:40PM -0400, Steven Rostedt wrote:
> > > From: Masami Hiramatsu <mhiramat@...nel.org>
> > > 
> > > Initialize kprobes at postcore_initcall level instead of module_init
> > > since kprobes is not a module, and it depends on only subsystems
> > > initialized in core_initcall.
> > > This will allow ftrace kprobe event to add new events when it is
> > > initializing because ftrace kprobe event is initialized at
> > > later initcall level.
> > > 
> > > Link: http://lkml.kernel.org/r/155851394736.15728.13626739508905120098.stgit@devnote2
> > > 
> > > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> > > Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> > > ---
> > >  kernel/kprobes.c | 3 +--
> > >  1 file changed, 1 insertion(+), 2 deletions(-)
> > > 
> > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > > index b1ea30a5540e..54aaaad00a47 100644
> > > --- a/kernel/kprobes.c
> > > +++ b/kernel/kprobes.c
> > > @@ -2289,6 +2289,7 @@ static int __init init_kprobes(void)
> > >  		init_test_probes();
> > >  	return err;
> > >  }
> > > +postcore_initcall(init_kprobes);  
> > 
> > As a heads-up, this is causing boot-time failures on arm64.
> 
> Thanks for the report.
> 
> > 
> > On arm64 kprobes depends on the BRK handler we register in
> > debug_traps_init(), which is an arch_initcall.
> > 
> > As of this change, init_krprobes() calls init_test_probes() before
> > that's registered, so we end up hitting a BRK before we can handle it.
> > 
> 
> Would something like this help?
> 
> -- Steve
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 5471efbeb937..0ca6f53c8505 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -2235,6 +2235,8 @@ static struct notifier_block kprobe_module_nb = {
>  extern unsigned long __start_kprobe_blacklist[];
>  extern unsigned long __stop_kprobe_blacklist[];
>  
> +static bool run_kprobe_tests __initdata;
> +
>  static int __init init_kprobes(void)
>  {
>  	int i, err = 0;
> @@ -2286,11 +2288,18 @@ static int __init init_kprobes(void)
>  	kprobes_initialized = (err == 0);
>  
>  	if (!err)
> -		init_test_probes();
> +		run_kprobe_tests = true;
>  	return err;
>  }
>  subsys_initcall(init_kprobes);


Just out of curious, if arm64's handler code initialized in arch_initcall,
why this subsys_initcall() function causes a problem?

This is actually related to my boot-time tracing series, so I would like
fix this issue without this patch.

Thank you,

>  
> +static int __init run_init_test_probes(void)
> +{
> +	if (run_kprobe_tests)
> +		init_test_probes();
> +}
> +module_init(run_init_test_probes);
> +
>  #ifdef CONFIG_DEBUG_FS
>  static void report_probe(struct seq_file *pi, struct kprobe *p,
>  		const char *sym, int offset, char *modname, struct kprobe *pp)
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>