linux-kernel - Re: [RFC PATCH V2] tracing: Check f_dentry before accessing event_file/call in inode->i

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Date:	Thu, 18 Jul 2013 11:20:36 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	jovi.zhangwei@...wei.com, Jiri Olsa <jolsa@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH V2] tracing: Check f_dentry before accessing event_file/call
 in inode->i_private

(2013/07/17 23:51), Oleg Nesterov wrote:
> On 07/17, Masami Hiramatsu wrote:
>>
>> (2013/07/16 3:16), Oleg Nesterov wrote:
>>> On 07/09, Masami Hiramatsu wrote:
>>>>
>>>> To avoid this, when opening events/*/*/enable, we have to ensure
>>>> the dentry of the file is not unlinked yet, under event_mutex
>>>> is locked.
>>>
>>> Probably this can work, but I am starting to think that this ref
>>> count becomes toooooo complex....
>>
>> Oleg, I agree that is a bit complex way to fix but it can fix.
>>
>> However, I think we should fix bugs first, because there are bugs.
>> I don't like to leave a bug in the kernel as it is, while we re-
>> start discussing new approach...
> 
> And I am trying to fix the same problems, just _I think_ there is
> another and simpler approach.

I see.
I also just feel uncomfortable with leaving obvious bugs, like as
having ants in my pants :)

>> So, I'd like to suggest you getting these fixes into ftrace as
>> first-aid treatment, and discuss your new series.
> 
> Well, perhaps you are right... But this TRACE_EVENT_FL_REF_MASK code
> is new too, it is not that we only need a small fixlets to finish it.

Would you mean that TRACE_EVENT_FL_REF_MASK may also have some problems?

> So I think that it makes sense to discuss the alternatives before we
> decide what exactly we should do.

Your approach is also interesting for me, indeed. However, it is so
different from current one. I think you should clarify what bug you
would like to solve and how. And we should clarify what ants^H^H^H^H
bugs we have found in ftrace too. ;)

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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