On Tue, Jun 13, 2017 at 11:28:41AM +0100, Will Deacon wrote: > page_ref_freeze and page_ref_unfreeze are designed to be used as a pair, > wrapping a critical section where struct pages can be modified without > having to worry about consistency for a concurrent fast-GUP. > > Whilst page_ref_freeze has full barrier semantics due to its use of > atomic_cmpxchg, page_ref_unfreeze is implemented using atomic_set, which > doesn't provide any barrier semantics and allows the operation to be > reordered with respect to page modifications in the critical section. > > This patch ensures that page_ref_unfreeze is ordered after any critical > section updates, by invoking smp_mb() prior to the atomic_set. > > Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> > Acked-by: Steve Capper <steve.capper@xxxxxxx> > Signed-off-by: Will Deacon <will.deacon@xxxxxxx> > --- > include/linux/page_ref.h | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h > index 610e13271918..1fd71733aa68 100644 > --- a/include/linux/page_ref.h > +++ b/include/linux/page_ref.h > @@ -174,6 +174,7 @@ static inline void page_ref_unfreeze(struct page *page, int count) > VM_BUG_ON_PAGE(page_count(page) != 0, page); > VM_BUG_ON(count == 0); > > + smp_mb(); Don't we want some comment here? Otherwise: Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
