mm: more rmap checking

Re-introduce rmap verification patches that Hugh removed when he removed
PG_map_lock. PG_map_lock actually isn't needed to synchronise access to
anonymous pages, because PG_locked and PTL together already do.

These checks were important in discovering and fixing a rare rmap corruption
in SLES9.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 8 deletions

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index bdd277223af0..97347f22fc20 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -74,17 +74,14 @@ void page_add_new_anon_rmap(struct page *, struct vm_area_struct *, unsigned lon
 void page_add_file_rmap(struct page *);
 void page_remove_rmap(struct page *, struct vm_area_struct *);
 
-/**
- * page_dup_rmap - duplicate pte mapping to a page
- * @page:       the page to add the mapping to
- *
- * For copy_page_range only: minimal extract from page_add_rmap,
- * avoiding unnecessary tests (already checked) so it's quicker.
- */
-static inline void page_dup_rmap(struct page *page)
+#ifdef CONFIG_DEBUG_VM
+void page_dup_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address);
+#else
+static inline void page_dup_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address)
 {
         atomic_inc(&page->_mapcount);
 }
+#endif
 
 /*
  * Called from mm/vmscan.c to handle paging out