linux-kernel - Re: + c-r-prctl-add-ability-to-set-new-mm_struct-exe_file-update-after-mm- num_exe_file

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Message-ID: <4F908CEB.8090606@openvz.org>
Date:	Fri, 20 Apr 2012 02:08:43 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
CC:	Oleg Nesterov <oleg@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"keescook@...omium.org" <keescook@...omium.org>,
	"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>,
	"matthltc@...ibm.com" <matthltc@...ibm.com>,
	"tj@...nel.org" <tj@...nel.org>,
	Pavel Emelianov <xemul@...allels.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: + c-r-prctl-add-ability-to-set-new-mm_struct-exe_file-update-after-mm-
 num_exe_file_vmas-removal.patch added to -mm tree

Cyrill Gorcunov wrote:
> On Thu, Apr 19, 2012 at 11:12:16PM +0200, Oleg Nesterov wrote:
>>> Heh :) Oleg, it was actually your idea to make this feature "one-shot".
>>
>> Heh, no ;)
>>
>> IIRC, I only asked you what do you actually want,
>>
>> 	Just one note for the record, prctl_set_mm_exe_file() does
>>
>> 		if (mm->num_exe_file_vmas)
>> 			return -EBUSY;
>>
>> 	We could do
>>
>> 		if (mm->exe_file)
>> 			return -EBUSY;
>>
>> 	This way "because this feature is a special to C/R" becomes
>> 	really true. IOW, you can't do PR_SET_MM_EXE_FILE twice.
>>
>> 	I am fine either way, just I want to ensure you really want
>> 	the current version.
>>
>> and only because it was documented as "feature is a special to C/R".
>
> ok, ubedil :)
>
>>> Once exe-file changed to a new value, it can't be changed again. The
>>> reason was to bring at least minimum disturbance in sysadmins life.
>>
>> You misunderstood. I am not arguing with "one-shot", I do not really
>> care.
>>
>> My question is: unless I missed something "it can't be changed again"
>> is not actually true. A task does PR_SET_MM_EXE_FILE, then it forks
>> the new child. The child can do PR_SET_MM_EXE_FILE again. Is this
>> by design?
>
> Hmm, not sure, Konstantin?

Why not? It has new pid, why it cannot change exe_file? Actually I don't care too.
But even if we include this bit into MMF_INIT_MASK we cannot forbid exe-file change
in childs tasks which was forked before exe-file change in parent.
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