return ret;
}
+/*
+ * FOLL_FORCE can write to even unwritable pmd's, but only
+ * after we've gone through a COW cycle and they are dirty.
+ */
+static inline bool can_follow_write_pmd(pmd_t pmd, struct page *page,
+ unsigned int flags)
+{
+ return pmd_write(pmd) ||
+ ((flags & FOLL_FORCE) && (flags & FOLL_COW) &&
+ page && PageAnon(page));
+}
+
struct page *follow_trans_huge_pmd(struct mm_struct *mm,
unsigned long addr,
pmd_t *pmd,
assert_spin_locked(&mm->page_table_lock);
- if (flags & FOLL_WRITE && !pmd_write(*pmd))
- goto out;
-
page = pmd_page(*pmd);
VM_BUG_ON(!PageHead(page));
+
+ if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, page, flags))
+ goto out;
+
if (flags & FOLL_TOUCH) {
pmd_t _pmd;
/*