From: Konstantin Khlebnikov <khlebnikov@openvz.org>
To: Matt Helsley <matthltc@us.ibm.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>,
Oleg Nesterov <oleg@redhat.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Eric Paris <eparis@redhat.com>,
"linux-security-module@vger.kernel.org"
<linux-security-module@vger.kernel.org>,
"oprofile-list@lists.sf.net" <oprofile-list@lists.sf.net>,
Linus Torvalds <torvalds@linux-foundation.org>,
Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH 6/7] mm: kill vma flag VM_EXECUTABLE
Date: Fri, 06 Apr 2012 01:04:43 +0400 [thread overview]
Message-ID: <4F7E08EB.5070600@openvz.org> (raw)
In-Reply-To: <20120405202904.GB7761@count0.beaverton.ibm.com>
Matt Helsley wrote:
> On Tue, Apr 03, 2012 at 11:32:04PM +0400, Cyrill Gorcunov wrote:
>> 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.
>
> The prctl() interface itself is fine as it stands now.
>
> As far as I can tell Konstantin is proposing that we remove the unusual
> counter that tracks the number of mappings of the exe_file and require
> userspace use the prctl() to drop the last reference. That's what I think
> will break the ABI because after that change you *must* change userspace
> code to use the prctl(). It's an ABI change because the same sequence of
> system calls with the same input bits produces different behavior.
But common software does not require this at all. I did not found real examples,
only hypothesis by Al Viro: https://lkml.org/lkml/2007/7/12/398
libhugetlbfs isn't good example too, the man proc says: /proc/[pid]/exe is alive until
main thread is alive, but in case libhugetlbfs /proc/[pid]/exe disappears too early.
Also I would not call it ABI, this corner-case isn't documented, I'm afraid only few
people in the world knows about it =)
next prev parent reply other threads:[~2012-04-05 21:04 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-31 9:25 [PATCH 0/7] mm: vma->vm_flags diet Konstantin Khlebnikov
2012-03-31 9:29 ` [PATCH 1/7] mm, x86, PAT: rework linear pfn-mmap tracking Konstantin Khlebnikov
2012-03-31 17:09 ` [PATCH 1/7 v2] " Konstantin Khlebnikov
2012-04-03 0:46 ` [x86 PAT PATCH 0/2] x86 PAT vm_flag code refactoring Suresh Siddha
2012-04-03 0:46 ` [x86 PAT PATCH 1/2] x86, pat: remove the dependency on 'vm_pgoff' in track/untrack pfn vma routines Suresh Siddha
2012-04-03 5:37 ` Konstantin Khlebnikov
2012-04-03 23:31 ` Suresh Siddha
2012-04-04 4:43 ` Konstantin Khlebnikov
2012-04-05 11:56 ` Konstantin Khlebnikov
2012-04-06 0:01 ` [v3 VM_PAT PATCH 0/3] x86 VM_PAT series Suresh Siddha
2012-04-06 0:01 ` [v3 VM_PAT PATCH 1/3] x86, pat: remove the dependency on 'vm_pgoff' in track/untrack pfn vma routines Suresh Siddha
2012-04-06 0:01 ` [v3 VM_PAT PATCH 2/3] x86, pat: separate the pfn attribute tracking for remap_pfn_range and vm_insert_pfn Suresh Siddha
2012-04-06 0:01 ` [v3 VM_PAT PATCH 3/3] mm, x86, PAT: rework linear pfn-mmap tracking Suresh Siddha
2012-04-03 0:46 ` [x86 PAT PATCH 2/2] " Suresh Siddha
2012-04-03 5:48 ` Konstantin Khlebnikov
2012-04-03 5:55 ` Konstantin Khlebnikov
2012-04-03 6:03 ` [x86 PAT PATCH 0/2] x86 PAT vm_flag code refactoring Konstantin Khlebnikov
2012-04-03 23:14 ` Suresh Siddha
2012-04-04 4:40 ` Konstantin Khlebnikov
2012-03-31 9:29 ` [PATCH 2/7] mm: introduce vma flag VM_ARCH_1 Konstantin Khlebnikov
2012-03-31 22:25 ` Benjamin Herrenschmidt
2012-03-31 9:29 ` [PATCH 3/7] mm: kill vma flag VM_CAN_NONLINEAR Konstantin Khlebnikov
2012-03-31 17:01 ` Linus Torvalds
2012-03-31 9:29 ` [PATCH 4/7] mm: kill vma flag VM_INSERTPAGE Konstantin Khlebnikov
2012-03-31 9:29 ` [PATCH 5/7] mm, drm/udl: fixup vma flags on mmap Konstantin Khlebnikov
2012-03-31 9:29 ` [PATCH 6/7] mm: kill vma flag VM_EXECUTABLE Konstantin Khlebnikov
2012-03-31 20:13 ` Oleg Nesterov
2012-03-31 20:39 ` Cyrill Gorcunov
2012-04-02 9:46 ` Konstantin Khlebnikov
2012-04-02 9:54 ` Cyrill Gorcunov
2012-04-02 10:13 ` Konstantin Khlebnikov
2012-04-02 14:48 ` Oleg Nesterov
2012-04-02 16:02 ` Cyrill Gorcunov
2012-04-02 16:19 ` Konstantin Khlebnikov
2012-04-02 16:27 ` Cyrill Gorcunov
2012-04-02 17:14 ` Konstantin Khlebnikov
2012-04-02 18:05 ` Cyrill Gorcunov
2012-04-02 23:04 ` Matt Helsley
2012-04-03 5:10 ` Konstantin Khlebnikov
2012-04-03 18:16 ` Matt Helsley
2012-04-03 19:32 ` Cyrill Gorcunov
2012-04-05 20:29 ` Matt Helsley
2012-04-05 20:53 ` Cyrill Gorcunov
2012-04-05 21:04 ` Konstantin Khlebnikov [this message]
2012-04-05 21:44 ` Matt Helsley
2012-04-05 21:55 ` Linus Torvalds
2012-04-06 4:36 ` Konstantin Khlebnikov
2012-04-02 23:18 ` Matt Helsley
2012-04-03 5:06 ` Konstantin Khlebnikov
2012-04-06 22:48 ` Andrew Morton
2012-03-31 9:29 ` [PATCH 7/7] mm: move madvise vma flags to the end Konstantin Khlebnikov
2012-03-31 14:06 ` [PATCH 0/7] mm: vma->vm_flags diet Andi Kleen
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4F7E08EB.5070600@openvz.org \
--to=khlebnikov@openvz.org \
--cc=akpm@linux-foundation.org \
--cc=eparis@redhat.com \
--cc=gorcunov@openvz.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-security-module@vger.kernel.org \
--cc=matthltc@us.ibm.com \
--cc=oleg@redhat.com \
--cc=oprofile-list@lists.sf.net \
--cc=torvalds@linux-foundation.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).