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Date: Tue, 3 Apr 2012 23:32:04 +0400
From: Cyrill Gorcunov <gorcunov@openvz.org>
To: Matt Helsley <matthltc@us.ibm.com>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>,
        Oleg Nesterov <oleg@redhat.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
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        Linus Torvalds <torvalds@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH 6/7] mm: kill vma flag VM_EXECUTABLE
Message-ID: <20120403193204.GE3370@moon>
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On Tue, Apr 03, 2012 at 11:16:31AM -0700, Matt Helsley wrote:
> On Tue, Apr 03, 2012 at 09:10:20AM +0400, Konstantin Khlebnikov wrote:
> > Matt Helsley wrote:
> > >On Sat, Mar 31, 2012 at 10:13:24PM +0200, Oleg Nesterov wrote:
> > >>On 03/31, Konstantin Khlebnikov wrote:
> > >>>
> > >>>comment from v2.6.25-6245-g925d1c4 ("procfs task exe symlink"),
> > >>>where all this stuff was introduced:
> > >>>
> > >>>>...
> > >>>>This avoids pinning the mounted filesystem.
> > >>>
> > >>>So, this logic is hooked into every file mmap/unmmap and vma split/merge just to
> > >>>fix some hypothetical pinning fs from umounting by mm which already unmapped all
> > >>>its executable files, but still alive. Does anyone know any real world example?
> > >>
> > >>This is the question to Matt.
> > >
> > >This is where I got the scenario:
> > >
> > >https://lkml.org/lkml/2007/7/12/398
> > 
> > Cyrill Gogcunov's patch "c/r: prctl: add ability to set new mm_struct::exe_file"
> > gives userspace ability to unpin vfsmount explicitly.
> 
> Doesn't that break the semantics of the kernel ABI?

Which one? exe_file can be changed iif there is no MAP_EXECUTABLE left.
Still, once assigned (via this prctl) the mm_struct::exe_file can't be changed
again, until program exit.

	Cyrill