linux-kernel - Re: Re: ftrace/kprobes: Warning when insmod two modules

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Date:	Tue, 22 Apr 2014 16:28:06 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Takao Indoh <indou.takao@...fujitsu.com>
Cc:	rusty@...tcorp.com.au, rostedt@...dmis.org, fweisbec@...il.com,
	mingo@...hat.com, ananth@...ibm.com,
	anil.s.keshavamurthy@...el.com, davem@...emloft.net,
	linux-kernel@...r.kernel.org
Subject: Re: Re: ftrace/kprobes: Warning when insmod two modules

(2014/04/22 14:29), Takao Indoh wrote:
> (2014/04/22 12:51), Rusty Russell wrote:
>> Steven Rostedt <rostedt@...dmis.org> writes:
>>> On Mon, 24 Mar 2014 20:26:05 +0900
>>> Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:
>>>
>>>
>>>> Thank you for reporting with this pretty backtrace :)
>>>> Steven, I think this is not the kprobe bug but ftrace (and perhaps, module).
>>>
>>> Looks to be more of a module issue than a ftrace issue.
>>>
>>>>
>>>> If the ftrace can set loading module text read only before the module subsystem
>>>> expected, I think it should be protected by the module subsystem itself
>>>> (e.g. set_all_modules_text_ro(rw) skips the modules which is MODULE_STATE_COMING)
>>>>
>>>
>>> Does this patch fix it?
>>>
>>> In-review-off-by: Steven Rostedt <rostedt@...dmis.org>
>>
>> Sorry, was on paternity leave.
>>
>> I'm always nervous about adding more states, since every place which
>> examines the state has to be audited.
>>
>> We set the mod->state to MOD_STATE_COMING in complete_formation;
>> why don't we set NX there instead?  It also makes more sense to
>> set NX before we hit parse_args() which can execute code in the module.
>>
>> In fact, we should probably call the notifier there too, so people
>> can breakpoint/tracepoint/etc parameter calls.
>>
>> Of course, this means that we set NX before the notifier; does anything
>> break?
> 
> This does not work. ftrace_process_locs() is called from the notifier,
> and it tries to change its text like this.
> 
> load_module
>   blocking_notifier_call_chain
>     ftrace_module_notify_enter
>       ftrace_init_module
>         ftrace_process_locs
>           sort
>             ftrace_swap_ips
> 
> But the text is already RO, so it causes panic. We need to call notifier
> before setting it RO. Or should we unset RO temporarily in
> ftrace_process_locs()?

Perhaps, IMHO, ftrace needs to change the module RW in ftrace_init_module and
makes it RO after modifying the module text.

Thank you,


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


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