Re: RFC: Cleanup / small fixes to hugetlb fault handling

["'David Gibson'" <david@gibson.dropbear.id.au>]

On Wed, Oct 26, 2005 at 11:44:52AM -0700, Chen, Kenneth W wrote:
> David Gibson wrote on Tuesday, October 25, 2005 7:49 PM
> > +int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
> > +		  unsigned long address, int write_access)
> > +{
> > +	pte_t *ptep;
> > +	pte_t entry;
> > +
> > +	ptep = huge_pte_alloc(mm, address);
> > +	if (! ptep)
> > +		/* OOM */
> > +		return VM_FAULT_SIGBUS;
> > +
> > +	entry = *ptep;
> > +
> > +	if (pte_none(entry))
> > +		return hugetlb_no_page(mm, vma, address, ptep);
> > +
> > +	/* we could get here if another thread instantiated the pte
> > +	 * before the test above */
> > +
> > +	return VM_FAULT_SIGBUS;
> >  }
> 
> Are you sure about the last return?  Looks like a typo to me, if *ptep
> is present, it should return VM_FAULT_MINOR.

Oops, yes, thinko.  Corrected patch shortly.

> But the bigger question is: don't you need some lock when checking *ptep?

No, I'm pretty sure that's ok.  In a sense, the test here is only an
optimization: we recheck the pte with lock held in hugetlb_no_page()
before attempting the set_pte_at().

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/people/dgibson
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