Subject: Re: [PATCH] sys_remap_file_pages: fix ->vm_file accounting
From: Matt Helsley <matthltc@us.ibm.com>
To: Oleg Nesterov <oleg@tv-sign.ru>
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, stable@kernel.org,
       linux-mm <linux-mm@kvack.org>
In-Reply-To: <20080130172646.GA2355@tv-sign.ru>
References: <20080130142014.GA2164@tv-sign.ru>
	 <1201712101.31222.22.camel@tucsk.pomaz.szeredi.hu>
	 <20080130172646.GA2355@tv-sign.ru>
Content-Type: text/plain
Organization: IBM Linux Technology Center
Date: Sat, 02 Feb 2008 12:52:38 -0800
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On Wed, 2008-01-30 at 20:26 +0300, Oleg Nesterov wrote:
> On 01/30, Miklos Szeredi wrote:
> > 
> > On Wed, 2008-01-30 at 17:20 +0300, Oleg Nesterov wrote:
> > > Fix ->vm_file accounting, mmap_region() may do do_munmap().
> > 
> > There's a small problem with the patch: the vma itself is freed at
> > unmap, so the fput(vma->vm_file) may crash.  Here's an updated patch.
> 
> Ah, indeed, thanks!
> 
> 
> 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.

Only shared VMAs can be remapped by sys_remap_file_pages but all
executable mappings are MAP_PRIVATE and hence lack the shared flag. I
don't know of a way for userspace to change that flag so I think there's
nothing that needs to be done here.

Cc'ing linux-mm.

Cheers,
	-Matt Helsley

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