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: <20120419220918.GA5474@redhat.com>
Date:	Fri, 20 Apr 2012 00:09:19 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	"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

On 04/20, Cyrill Gorcunov wrote:
>
> Guys, while I more-less agree with Matt about single-shot behaviour
>
> [ let me copy my and his email
>
>   >> With mm->exe_file this prctl option become a one-shot
>   >> only, and while at moment our user-space tool can perfectly
>   >> live with that I thought that there is no strict need to
>   >> limit the option this way from the very beginning.
>   >>
>   > As far as backward compatibility, isn't it better to lift that restriction
>   > later rather than add it? I think the latter would very likely "break"
>   > things whereas the former would not.
>   >
>   > I also prefer that restriction because it establishes a bound on how
>   > frequently the symlink can change. Keeping it a one-shot deal makes the
>   > values that show up in tools like top more reliable for admins.
> ]
>
> I guess maybe it's time to drop one-shot requirement and as result
> we can drop MMF_EXE_FILE_CHANGED bit completely,

Plus perhaps we can remove this for_each_vma check?

> making overall code
> simplier?

Personally I'd certainly prefer this ;)



But let me repeat to avoid the confusion. I am fine either way,
I am not going to discuss this again unless I see something which
looks technically wrong. And the current MMF_EXE_FILE_CHANGED
doesn't look right even if the problem is minor.

Oleg.

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