Re: [PATCH 1/3] revoke: misc fixes

[Nick Piggin]

Pekka J Enberg wrote:
> 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...

Could you try something like walk the i_mmap lists to find mms with vmas that
haven't need revoking, then each time you find one, take a ref on the mm, drop
i_mmap_lock, take mmap_sem, and walk all its vmas looking for any that reference
the inode?

Bit of a roundabout way to go, but it might work.

--
SUSE Labs, Novell Inc.
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