linux-kernel - Re: BUG: Kprobe smoke test: 2 out of 6 tests failed

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Message-ID: <503DCE13.5030400@hitachi.com>
Date:	Wed, 29 Aug 2012 17:08:51 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Wu Fengguang <fengguang.wu@...el.com>
Subject: Re: BUG: Kprobe smoke test: 2 out of 6 tests failed

Hi Steven and Fengguang,

(2012/08/25 10:00), Steven Rostedt wrote:
> On Fri, 2012-08-24 at 09:41 -0400, Steven Rostedt wrote:
> 
>> On Fri, 2012-08-24 at 15:15 +0800, Fengguang Wu wrote:
>>> Hi Steven,
>>>
>>> The following test fails are mostly due to this commit, or one of the
>>> last 4 commits in
>>>
>>> tree:   git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git tip/perf/core
>>> head:   d57c5d51a30152f3175d2344cb6395f08bf8ee0c
>>> commit: d57c5d51a30152f3175d2344cb6395f08bf8ee0c [100/100] ftrace/x86: Add support for -mfentry to x86_64
>>>
>>> [    9.084881] Kprobe smoke test failed: register_jprobe returned -22
>>> [    9.086786] Kprobe smoke test failed: register_jprobes returned -22
> 
> Masami,
> 
> Seems that when we use fentry, we break jprobes. I thought the patches
> that we added would just move the call to the next op, not fail totally?

Ah! yes, it would be kprobe-side problem.

Since ftrace_regs_call allows handlers to set regs->ip, it is not necessarily
to move jprobe onto the next instruction (even it will be the simplest one).
Instead, I think we can allow it on ftrace entries. Of course, ftrace side
change is also needed, e.g. sorting handlers for moving such ip-modifying
handler to the last.

Thank you,


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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