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Date: Thu, 12 Dec 2013 19:31:46 +0900
From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Organization: Hitachi, Ltd., Japan
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To: Jiri Kosina <jkosina@suse.cz>
Cc: Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
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        Frederic Weisbecker <fweisbec@gmail.com>, x86@kernel.org,
        lkml <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@redhat.com>, systemtap@sourceware.org,
        "H. Peter Anvin" <hpa@zytor.com>, Sasha Levin <sasha.levin@oracle.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Seiji Aguchi <seiji.aguchi@hds.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH -tip v4 6/6] [RFC] kprobes/x86: Call exception handlers
 directly from do_int3/do_debug
References: <20131204012841.22118.82992.stgit@kbuild-fedora.novalocal> <20131204012856.22118.91079.stgit@kbuild-fedora.novalocal> <20131203213904.5ff1794c@gandalf.local.home> <alpine.LRH.2.00.1312111418550.6318@twin.jikos.cz> <52A93E3A.9080600@hitachi.com> <alpine.LNX.2.00.1312121058220.1413@pobox.suse.cz>
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(2013/12/12 18:59), Jiri Kosina wrote:
> On Thu, 12 Dec 2013, Masami Hiramatsu wrote:
> 
>>> Yeah, it's broken. Obviously, if you happen to trigger int3 before the 
>>> notifier has been registered, it'd cause int3 exception to be unhandled. 
>>> See
>>>
>>> 	commit 17f41571bb2c4a398785452ac2718a6c5d77180e
>>> 	Author: Jiri Kosina <jkosina@suse.cz>
>>> 	Date:   Tue Jul 23 10:09:28 2013 +0200
>>>
>>> 	    kprobes/x86: Call out into INT3 handler directly instead of using notifier
>>>
>>> for one such issue that happened with jump labels.
>>>
>>>> Hmm, if there's no users of the int3 notifier, should we just remove it?
>>>
>>> Hmm, there are still uprobes, right?
>>
>> Right, uprobes still use it, however, since it only handles user-space
>> breakpoint, there is no problem.
> 
> Agreed. But therefore the notifier can't just be removed, unless uprobes 
> are converted to direct call as well (but I don't think that'd be 
> beneficial, notifier is sufficient in this case).

Ah, I don't intended to remove notify_die from do_int3, since
notify_die notifies many other exceptions too. :)

Thank you,

-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com