linux-kernel - Re: [PATCH -tip v4 6/6] [RFC] kprobes/x86: Call exception handlers directly from do_int3/do

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Message-ID: <20131203213904.5ff1794c@gandalf.local.home>
Date:	Tue, 3 Dec 2013 21:39:04 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Ingo Molnar <mingo@...nel.org>, Andi Kleen <ak@...ux.intel.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>,
	Frederic Weisbecker <fweisbec@...il.com>, x86@...nel.org,
	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>, systemtap@...rceware.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Seiji Aguchi <seiji.aguchi@....com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH -tip v4 6/6] [RFC] kprobes/x86: Call exception handlers
 directly from do_int3/do_debug

On Wed, 04 Dec 2013 01:28:56 +0000
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:

> To avoid a kernel crash by probing on lockdep code, call
> kprobe_int3_handler and kprobe_debug_handler directly
> from do_int3 and do_debug. Since there is a locking code
> in notify_die, lockdep code can be invoked. And because
> the lockdep involves printk() related things, theoretically,
> we need to prohibit probing on much more code...
> 
> Anyway, most of the int3 handlers in the kernel are already
> called from do_int3 directly, e.g. ftrace_int3_handler,
> poke_int3_handler, kgdb_ll_trap. Actually only
> kprobe_exceptions_notify is on the notifier_call_chain.
> 
> So I think this is not a crazy thing.

What? Oh, yeah. No, using notifiers in int3 handler is the crazy
thing ;-)

Hmm, if there's no users of the int3 notifier, should we just remove it?

-- Steve
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