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: <20120419210033.GO1893@moon>
Date:	Fri, 20 Apr 2012 01:00:33 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	akpm@...ux-foundation.org, khlebnikov@...nvz.org,
	keescook@...omium.org, kosaki.motohiro@...fujitsu.com,
	matthltc@...ibm.com, tj@...nel.org, xemul@...allels.com,
	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 Thu, Apr 19, 2012 at 09:20:05PM +0200, Oleg Nesterov wrote:
> On 04/19, Andrew Morton wrote:
> >
> > From: Konstantin Khlebnikov <khlebnikov@...nvz.org>
> > Subject: c/r: prctl: update prctl_set_mm_exe_file() after mm->num_exe_file_vmas removal
> >
> > [ fix for "c-r-prctl-add-ability-to-set-new-mm_struct-exe_file-v2" from mm tree ]
> >
> > After removing mm->num_exe_file_vmas kernel keeps mm->exe_file until final
> > mmput(), it never becomes NULL while task is alive.
> >
> > We can check for other mapped files in mm instead of checking
> > mm->num_exe_file_vmas, and mark mm with flag MMF_EXE_FILE_CHANGED in order
> > to forbid second changing of mm->exe_file.
> 
> I lost the track a long ago.
> 
> Just one question, what does this "forbid second changing" actually mean?

Heh :) Oleg, it was actually your idea to make this feature "one-shot".
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.

	Cyrill
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