linux-kernel - Re: [BUG?]3.0-rc4+ftrace+kprobe: set kprobe at instruction 'stwu' lead to system crash/freeze

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Date:	Fri, 02 Dec 2011 08:37:48 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	"tiejun.chen" <tiejun.chen@...driver.com>
Cc:	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Anton Blanchard <anton@....ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Yong Zhang <yong.zhang0@...il.com>, paulus@...ba.org,
	yrl.pp-manager.tt@...achi.com,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [BUG?]3.0-rc4+ftrace+kprobe: set kprobe at instruction 'stwu'
 lead to system crash/freeze

On Thu, 2011-12-01 at 18:44 +0800, tiejun.chen wrote:

> Do you mean we should push the original pt_regs (or that whole exception stack)
> downwards the location the new r1 point? Then its safe to perform this real
> emulated stw instruction. At last we will reroute r1 to that copied exception
> frame to restore as normal. Right?

Right. That way we don't have to modify the (sensitive) restore path, we
only hook around the do_work branch which is a lot easier and less
risky.

> Here I suppose so, I implement this for PPC32 based on the above understanding.
> I take a validation for kprobing do_fork()/show_interrupts(), now looks fine.
> Tomorrow I will go PPC64, and hope its fine as well.
> 
> If everything is good I'll send these patches to linuxppc-dev next week.

Excellent, thanks !

Cheers,
Ben.


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