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Date:   Wed, 28 Mar 2018 14:21:29 -0700 (PDT)
From:   David Rientjes <rientjes@google.com>
To:     Laurent Dufour <ldufour@linux.vnet.ibm.com>
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Subject: Re: [PATCH v9 09/24] mm: protect mremap() against SPF hanlder
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On Wed, 28 Mar 2018, Laurent Dufour wrote:

> >> @@ -326,7 +336,10 @@ static unsigned long move_vma(struct vm_area_struct *vma,
> >>  		mremap_userfaultfd_prep(new_vma, uf);
> >>  		arch_remap(mm, old_addr, old_addr + old_len,
> >>  			   new_addr, new_addr + new_len);
> >> +		if (vma != new_vma)
> >> +			vm_raw_write_end(vma);
> >>  	}
> >> +	vm_raw_write_end(new_vma);
> > 
> > Just do
> > 
> > vm_raw_write_end(vma);
> > vm_raw_write_end(new_vma);
> > 
> > here.
> 
> Are you sure ? we can have vma = new_vma done if (unlikely(err))
> 

Sorry, what I meant was do

if (vma != new_vma)
	vm_raw_write_end(vma);
vm_raw_write_end(new_vma);

after the conditional.  Having the locking unnecessarily embedded in the 
conditional has been an issue in the past with other areas of core code, 
unless you have a strong reason for it.