linux-kernel - Re: [PATCH 1/3] revoke: misc fixes

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Message-ID: <Pine.LNX.4.64.0703160927240.14902@sbz-30.cs.Helsinki.FI>
Date:	Fri, 16 Mar 2007 09:29:08 +0200 (EET)
From:	Pekka J Enberg <penberg@...helsinki.fi>
To:	Nick Piggin <nickpiggin@...oo.com.au>
cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] revoke: misc fixes

Pekka J Enberg wrote:
> > 	/*
> > - 	 * Not holding ->mmap_sem here.
> > + 	 * Not holding ->mmap_sem here but we must watch out for page
> > + 	 * faults and after the shared mappings have been taken down
> > + 	 * and sys_mmap() trying to remap the revoked range.
> >   */
> >   vma->vm_flags |= VM_REVOKED;
> >   smp_mb();
> > @@ -455,7 +457,7 @@ 	int err = 0;

On Fri, 16 Mar 2007, Nick Piggin wrote:
> You're still modifying vm_flags without down_write mmap_sem, so this will
> corrupt vm_flags.

Uhm, you're right, two concurrent writes and we can lose some bits so a 
barrier doesn't work. Too bad as we're under mapping->i_mmap_lock here and 
thus cannot take ->mmap_sep...
-
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