linux-kernel - Re: [PATCH/RFC 17/17] tracing/uprobes: Add @+file

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Message-ID: <87ob54oxzt.fsf@sejong.aot.lge.com>
Date:	Fri, 29 Nov 2013 09:25:10 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hyeoncheol Lee <cheol.lee@....com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	"zhangwei\(Jovi\)" <jovi.zhangwei@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Namhyung Kim <namhyung.kim@....com>
Subject: Re: [PATCH/RFC 17/17] tracing/uprobes: Add @+file_offset fetch method

Hi Oleg,

On Thu, 28 Nov 2013 17:31:48 +0100, Oleg Nesterov wrote:
> On 11/28, Namhyung Kim wrote:
>>
>> I thought we need a fetch_param anyway if we will add support for
>> cross-fetch later.  But I won't insist it strongly, I can delay it to
>> later work and make current code simpler if you want. :)
>
> OK, great,

So do you want me to change to make it simpler without a fetch_param?

>
>> >>  static int uprobe_dispatcher(struct uprobe_consumer *con, struct pt_regs *regs)
>> >>  {
>> >>  	struct trace_uprobe *tu;
>> >> +	struct uprobe_task *utask;
>> >>  	int ret = 0;
>> >>
>> >>  	tu = container_of(con, struct trace_uprobe, consumer);
>> >>  	tu->nhit++;
>> >>
>> >> +	utask = current->utask;
>> >> +	if (utask == NULL)
>> >> +		return UPROBE_HANDLER_REMOVE;
>> >
>> > Hmm, why? The previous change ensures ->utask is not NULL? If we hit
>> > NULL we have a bug, we should not remove this uprobe.
>>
>> Yes, I just want to be defensive. :)
>>
>> So do you suggest to add BUG_ON()?
>
> We are going to crash with the same effect if it is NULL ;)

I see.  I'll just get rid of the if (...) part.

>
>> And can I convert or remove a
>> similar check in uprobes.c:pre_ssout() too?
>
> Well, yes, we _can_ do this. But unless you have the strong opinion
> I'd suggest to not do this. At least right now.
>
> To remind, perhaps we can revert the previous patch later if we find
> a better solution (placeholder).

OK, I'll just leave it as is.

>
> And. Note that we will change this code in any case. I suggested to
> use ->vaddr to avoid the other (potentially conflicting) changes in
> uprobes.h. Even if we use current->utask, we should add another member
> into the union. But again, it would be better to do this later, and
> the change will be trivial.

Got it.  Thank you for the explanation.

Thanks,
Namhyung
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