[On behalf of justin...@arm.com]
Hi Matthew
On 2019/9/20 23:53, Matthew Wilcox wrote:
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.
Ok, will change the return type to bool as you suggested.
Thanks
---
Cheers,
Justin (Jia He)
