Re: [PATCH v5 1/5] mm: add vm_insert_mixed_mkwrite()
On Mon, Jul 24, 2017 at 11:06:12AM -0600, Ross Zwisler wrote:
@@ -1658,14 +1658,35 @@ static int insert_pfn(struct vm_area_struct
*vma, unsigned long addr,
if (!pte)
goto out;
retval = -EBUSY;
- if (!pte_none(*pte))
- goto out_unlock;
+ if (!pte_none(*pte)) {
+ if (mkwrite) {
+ /*
+ * For read faults on private mappings the PFN passed
+ * in may not match the PFN we have mapped if the
+ * mapped PFN is a writeable COW page. In the mkwrite
+ * case we are creating a writable PTE for a shared
+ * mapping and we expect the PFNs to match.
+ */
Can we?
I guess it's up to filesystem if it wants to reuse the same spot to write
data or not. I think your assumptions works for ext4 and xfs. I wouldn't
be that sure for btrfs or other filesystems with CoW support.
--
Kirill A. Shutemov