Re: [PATCH 1/2] sparc: Fix handling of page table constructor failure

Matthew Wilcox
2020-11-25T12:11:02Z

On Wed, Nov 25, 2020 at 09:43:15AM +0100, David Hildenbrand wrote:
> On 25.11.20 04:46, Matthew Wilcox (Oracle) wrote:
> > The page has just been allocated, so its refcount is 1. free_unref_page()
> > is for use on pages which have a zero refcount. Use __free_page()
> > like the other implementations of pte_alloc_one().
> >
> > Fixes: 1ae9ae5f7df7 ("sparc: handle pgtable_page_ctor() fail")
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> > ---
> > arch/sparc/mm/init_64.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
> > index 96edf64d4fb3..182bb7bdaa0a 100644
> > --- a/arch/sparc/mm/init_64.c
> > +++ b/arch/sparc/mm/init_64.c
> > @@ -2894,7 +2894,7 @@ pgtable_t pte_alloc_one(struct mm_struct *mm)
> > if (!page)
> > return NULL;
> > if (!pgtable_pte_page_ctor(page)) {
> > - free_unref_page(page);
> > + __free_page(page);
> > return NULL;
> > }
> > return (pte_t *) page_address(page);
> >
>
> I wonder if reusing __pte_alloc_one() - e.g., internally - would be even
> cleaner.

It's really awkward to do because pgtable_t is defined differently.
The clean thing to do would be:

--- arch/sparc/include/asm/page_64.h
-typedef pte_t *pgtable_t;
+typedef struct page *pgtable_t;

and then do all the other changes that would require.

But that feels like a lot more work than appropriate to fix this
unlikely bug.