Revert "mm, thp: Do not make pmd/pud dirty without a reason"

This reverts commit 152e93af3c.

It was a nice cleanup in theory, but as Nicolai Stange points out, we do
need to make the page dirty for the copy-on-write case even when we
didn't end up making it writable, since the dirty bit is what we use to
check that we've gone through a COW cycle.

Reported-by: Michal Hocko <mhocko@kernel.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory.c

@@ -3335,7 +3335,7 @@ static int do_set_pmd(struct vm_fault *vmf, struct page *page)
 
 	entry = mk_huge_pmd(page, vma->vm_page_prot);
 	if (write)
-		entry = maybe_pmd_mkwrite(entry, vma, true);
+		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
 
 	add_mm_counter(vma->vm_mm, MM_FILEPAGES, HPAGE_PMD_NR);
 	page_add_file_rmap(page, true);