mm/rmap: move folio_test_anon() check out of __folio_set_anon()

Let's handle it in the caller; no need for the "first" check based on the
mapcount.

We really only end up with !anon pages in page_add_anon_rmap() via
do_swap_page(), where we hold the folio lock.  So races are not possible.
Add a VM_WARN_ON_FOLIO() to make sure that we really hold the folio lock.

In the future, we might want to let do_swap_page() use
folio_add_new_anon_rmap() on new pages instead: however, we might have to
pass then whether the folio is exclusive or not.  So keep it in there for
now.

For hugetlb we never expect to have a non-anon page in
hugepage_add_anon_rmap().  Remove that code, along with some other checks
that are either not required or were checked in
hugepage_add_new_anon_rmap() already.

Link: https://lkml.kernel.org/r/20230913125113.313322-4-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/rmap.c b/mm/rmap.c
index f76f0f23725c4940481f013fe3822032598b39c0..65de3832123ef2cc94579c3a2d8e643f26e4ad01 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1135,9 +1135,6 @@ static void __folio_set_anon(struct folio *folio, struct vm_area_struct *vma,
 
        BUG_ON(!anon_vma);
 
-       if (folio_test_anon(folio))
-               return;
-
        /*
         * If the folio isn't exclusive to this vma, we must use the _oldest_
         * possible anon_vma for the folio mapping!
@@ -1239,12 +1236,12 @@ void page_add_anon_rmap(struct page *page, struct vm_area_struct *vma,
        if (nr)
                __lruvec_stat_mod_folio(folio, NR_ANON_MAPPED, nr);
 
-       if (likely(!folio_test_ksm(folio))) {
-               if (first)
-                       __folio_set_anon(folio, vma, address,
-                                        !!(flags & RMAP_EXCLUSIVE));
-               else
-                       __page_check_anon_rmap(folio, page, vma, address);
+       if (unlikely(!folio_test_anon(folio))) {
+               VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio);
+               __folio_set_anon(folio, vma, address,
+                                !!(flags & RMAP_EXCLUSIVE));
+       } else if (likely(!folio_test_ksm(folio))) {
+               __page_check_anon_rmap(folio, page, vma, address);
        }
        if (flags & RMAP_EXCLUSIVE)
                SetPageAnonExclusive(page);
@@ -2541,17 +2538,13 @@ void hugepage_add_anon_rmap(struct page *page, struct vm_area_struct *vma,
                            unsigned long address, rmap_t flags)
 {
        struct folio *folio = page_folio(page);
-       struct anon_vma *anon_vma = vma->anon_vma;
        int first;
 
-       BUG_ON(!folio_test_locked(folio));
-       BUG_ON(!anon_vma);
+       VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
+
        first = atomic_inc_and_test(&folio->_entire_mapcount);
        VM_BUG_ON_PAGE(!first && (flags & RMAP_EXCLUSIVE), page);
        VM_BUG_ON_PAGE(!first && PageAnonExclusive(page), page);
-       if (first)
-               __folio_set_anon(folio, vma, address,
-                                !!(flags & RMAP_EXCLUSIVE));
        if (flags & RMAP_EXCLUSIVE)
                SetPageAnonExclusive(page);
 }