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

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Date:   Wed, 3 Jul 2019 14:50:38 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [for-next][PATCH 12/16] kprobes: Initialize kprobes at
 postcore_initcall

On Tue, Jul 02, 2019 at 05:50:09PM +0100, Mark Rutland 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.
> 
> 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.

Thanks Mark for identifying this.

So we either revert the above commit in -next or queue the one below
together with the rest of the kprobes changes (I can queue it via the
arm64 for-next/core assuming that the above commit id remains stable):

--------------8<------------------------------------
>From de4f4d30bab3d77d6643a6fa9ba1deff73dac7f2 Mon Sep 17 00:00:00 2001
From: Catalin Marinas <catalin.marinas@....com>
Date: Wed, 3 Jul 2019 14:44:23 +0100
Subject: [PATCH] arm64: Initialise the debug traps earlier

Commit b5f8b32c93b2 ("kprobes: Initialize kprobes at postcore_initcall")
makes init_kprobes() a postcore_initcall while the arm64 handling of the
BRK instruction is initialised at arch_initcall level. Make the arm64
debug_traps_init() a core_initcall.

Fixes: b5f8b32c93b2 ("kprobes: Initialize kprobes at postcore_initcall")
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
---
 arch/arm64/kernel/debug-monitors.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
index f8719bd30850..81770105cd8e 100644
--- a/arch/arm64/kernel/debug-monitors.c
+++ b/arch/arm64/kernel/debug-monitors.c
@@ -382,7 +382,7 @@ static int __init debug_traps_init(void)
 			      TRAP_BRKPT, "ptrace BRK handler");
 	return 0;
 }
-arch_initcall(debug_traps_init);
+core_initcall(debug_traps_init);
 
 /* Re-enable single step for syscall restarting. */
 void user_rewind_single_step(struct task_struct *task)