Messages in this thread | | | Date | Fri, 20 Sep 2019 08:53:00 -0700 | From | Matthew Wilcox <> | Subject | Re: [PATCH v7 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared |
| |
On Fri, Sep 20, 2019 at 09:54:37PM +0800, Jia He wrote: > -static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma) > +static inline int cow_user_page(struct page *dst, struct page *src, > + struct vm_fault *vmf) > {
Can we talk about the return type here?
> + } else { > + /* Other thread has already handled the fault > + * and we don't need to do anything. If it's > + * not the case, the fault will be triggered > + * again on the same address. > + */ > + pte_unmap_unlock(vmf->pte, vmf->ptl); > + return -1; ... > + return 0; > }
So -1 for "try again" and 0 for "succeeded".
> + if (cow_user_page(new_page, old_page, vmf)) {
Then we use it like a bool. But it's kind of backwards from a bool because false is success.
> + /* COW failed, if the fault was solved by other, > + * it's fine. If not, userspace would re-fault on > + * the same address and we will handle the fault > + * from the second attempt. > + */ > + put_page(new_page); > + if (old_page) > + put_page(old_page); > + return 0;
And we don't use the return value; in fact we invert it.
Would this make more sense:
static inline bool cow_user_page(struct page *dst, struct page *src, struct vm_fault *vmf) ... pte_unmap_unlock(vmf->pte, vmf->ptl); return false; ... return true; ... if (!cow_user_page(new_page, old_page, vmf)) {
That reads more sensibly for me. We could also go with returning a vm_fault_t, but that would be more complex than needed today, I think.
| |