linux-kernel - Re: [PATCH 6/7] mm: kill vma flag VM

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Date:	Mon, 2 Apr 2012 20:02:53 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Eric Paris <eparis@...hat.com>
Subject: Re: [PATCH 6/7] mm: kill vma flag VM_EXECUTABLE

On Mon, Apr 02, 2012 at 04:48:21PM +0200, Oleg Nesterov wrote:
> On 04/02, Konstantin Khlebnikov wrote:
> >
> > In this patch I leave mm->exe_file lockless.
> > After exec/fork we can change it only for current task and only if mm->mm_users == 1.
> >
> > something like this:
> >
> > task_lock(current);
> 
> OK, this protects against the race with get_task_mm()
> 
> > if (atomic_read(&current->mm->mm_users) == 1)
> 
> this means PR_SET_MM_EXE_FILE can fail simply because someone did
> get_task_mm(). Or the caller is multithreaded.

So it leads to the same question -- do we *really* need the PR_SET_MM_EXE_FILE
to be one-shot action? Yeah, I know, we agreed that one-shot is better than
anything else from sysadmin perspective and such, but maybe I could introduce
a special capability bit for c/r and allow a program which has such cap to modify
exe-file without checkin mm_users?

/me hides

> 
> > 	set_mm_exe_file(current->mm, new_file);
> 
> No, fput() can sleep.

Sure, it was just "something like" as Konstantin stated, thanks anyway ;)

	Cyrill
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