linux-kernel - Re: Re: [PATCH 16/17] uprobes: Allocate ->utask before handler

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Date:	Thu, 12 Dec 2013 14:55:57 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Namhyung Kim <namhyung@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Hyeoncheol Lee <cheol.lee@....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: Re: [PATCH 16/17] uprobes: Allocate ->utask before handler_chain()
 for tracing handlers

(2013/12/12 3:11), Oleg Nesterov wrote:
> On 12/11, Masami Hiramatsu wrote:
>>
>> (2013/12/11 0:57), Oleg Nesterov wrote:
>>> On 12/10, Masami Hiramatsu wrote:
>>>>
>>>> and isn't it better to increment
>>>> miss-hit counter of the uprobe?
>>>
>>> What do you mean? This is not miss-hit and ->utask == NULL is quite normal.
>>
>> But it could skip the handler_chain silently. It could confuse users
>> why their probe doesn't hit as expected.
> 
> No, we will restart the same (probed) instruction, handle_swbp()
> will be called again, get_utask() will be called again.

Hmm, in that case, how would you avoid infinite recursive loop??
Would you repeat it until get_utask() != NULL?

> Not to mention that (in practice) if GFP_KERNEL fails the task is
> already killed.
> 
>>> For example, on ppc it can be always NULL because ppc likely emulates the
>>> probed insn.
>>
>> Hmm, in that case, should uprobes handlers never be called on ppc with
>> this change?
> 
> Why? With this change ppc will have ->utask != NULL even if it doesn't
> need it at all.

Ah, I see. This changes that.

Thank you,

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


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