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From: Oleg Nesterov <oleg@tv-sign.ru>
To: Matt Helsley <matthltc@us.ibm.com>
Cc: Miklos Szeredi <mszeredi@suse.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	William Lee Irwin III <wli@holomorphy.com>,
	Nick Piggin <nickpiggin@yahoo.com.au>,
	Ingo Molnar <mingo@elte.hu>,
	linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org>
Subject: Re: [PATCH] sys_remap_file_pages: fix ->vm_file accounting
Date: Sun, 3 Feb 2008 21:21:35 +0300	[thread overview]
Message-ID: <20080203182135.GA5827@tv-sign.ru> (raw)
In-Reply-To: <1201987065.9062.6.camel@localhost.localdomain>

(remove stable@kernel.org from CC)

On 02/02, Matt Helsley wrote:
> 
> On Wed, 2008-01-30 at 20:26 +0300, Oleg Nesterov wrote:
> > 
> > Offtopic. I noticed this problem while looking at this patch:
> > 
> > 	http://marc.info/?l=linux-mm-commits&m=120141116911711
> > 
> > So this (the old vma could be removed before we create the new mapping)
> > means that the patch above has another problem: if we are remapping the
> > whole VM_EXECUTABLE vma, removed_exe_file_vma() can clear ->exe_file
> > while it shouldn't (Matt Helsley cc'ed).
> > 
> > Oleg.
> 
> 	Looking at sys_remap_file_pages() it appears that the shared flag must
> be set in order to remap. Executable mappings are always MAP_PRIVATE and
> hence lack the shared flag so that any modifications to those areas
> don't get written back to the executable. I don't think userspace can
> change this flag

Yes, userspace can't change it. But if MVFS changes ->vm_file it could also
change vm_flags... But I think you are right anyway, we shouldn't care.


So I have to try to find another bug ;) Suppose that ->load_binary() does
a series of do_mmap(MAP_EXECUTABLE). It is possible that mmap_region() can
merge 2 vmas. In that case we "leak" ->num_exe_file_vmas. Unless I missed
something, mmap_region() should do removed_exe_file_vma() when vma_merge()
succeds (near fput(file)).

Oleg.


  reply	other threads:[~2008-02-03 18:19 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-30 14:20 Oleg Nesterov
2008-01-30 16:55 ` Miklos Szeredi
2008-01-30 17:26   ` Oleg Nesterov
2008-02-02 20:52     ` Matt Helsley
2008-02-02 21:17     ` Matt Helsley
2008-02-03 18:21       ` Oleg Nesterov [this message]
2008-02-06 20:33         ` Hugh Dickins
2008-02-07  0:16           ` Matt Helsley
2008-02-07 16:40             ` Hugh Dickins
2008-02-03 18:29     ` Oleg Nesterov
2008-02-06 20:13       ` Hugh Dickins
2008-02-11 10:15         ` Oleg Nesterov

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