[PATCH] mm: more rmap debugging

Add more debugging in the rmap code in an attempt to locate to source of
the occasional "mapcount went negative" assertions.

Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/rmap.h

@@ -72,7 +72,7 @@ void __anon_vma_link(struct vm_area_struct *);
 void page_add_anon_rmap(struct page *, struct vm_area_struct *, unsigned long);
 void page_add_new_anon_rmap(struct page *, struct vm_area_struct *, unsigned long);
 void page_add_file_rmap(struct page *);
-void page_remove_rmap(struct page *);
+void page_remove_rmap(struct page *, struct vm_area_struct *);
 
 /**
  * page_dup_rmap - duplicate pte mapping to a page

mm/filemap_xip.c

@@ -189,7 +189,7 @@ __xip_unmap (struct address_space * mapping,
 			/* Nuke the page table entry. */
 			flush_cache_page(vma, address, pte_pfn(*pte));
 			pteval = ptep_clear_flush(vma, address, pte);
-			page_remove_rmap(page);
+			page_remove_rmap(page, vma);
 			dec_mm_counter(mm, file_rss);
 			BUG_ON(pte_dirty(pteval));
 			pte_unmap_unlock(pte, ptl);

mm/fremap.c

@@ -33,7 +33,7 @@ static int zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,
 		if (page) {
 			if (pte_dirty(pte))
 				set_page_dirty(page);
-			page_remove_rmap(page);
+			page_remove_rmap(page, vma);
 			page_cache_release(page);
 		}
 	} else {

mm/memory.c

@@ -681,7 +681,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 					mark_page_accessed(page);
 				file_rss--;
 			}
-			page_remove_rmap(page);
+			page_remove_rmap(page, vma);
 			tlb_remove_page(tlb, page);
 			continue;
 		}
@@ -1586,7 +1586,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
 	if (likely(pte_same(*page_table, orig_pte))) {
 		if (old_page) {
-			page_remove_rmap(old_page);
+			page_remove_rmap(old_page, vma);
 			if (!PageAnon(old_page)) {
 				dec_mm_counter(mm, file_rss);
 				inc_mm_counter(mm, anon_rss);

mm/rmap.c

@@ -47,6 +47,7 @@
 #include <linux/rmap.h>
 #include <linux/rcupdate.h>
 #include <linux/module.h>
+#include <linux/kallsyms.h>
 
 #include <asm/tlbflush.h>
 
@@ -567,14 +568,20 @@ void page_add_file_rmap(struct page *page)
  *
  * The caller needs to hold the pte lock.
  */
-void page_remove_rmap(struct page *page)
+void page_remove_rmap(struct page *page, struct vm_area_struct *vma)
 {
 	if (atomic_add_negative(-1, &page->_mapcount)) {
 		if (unlikely(page_mapcount(page) < 0)) {
 			printk (KERN_EMERG "Eeek! page_mapcount(page) went negative! (%d)\n", page_mapcount(page));
+			printk (KERN_EMERG "  page pfn = %lx\n", page_to_pfn(page));
 			printk (KERN_EMERG "  page->flags = %lx\n", page->flags);
 			printk (KERN_EMERG "  page->count = %x\n", page_count(page));
 			printk (KERN_EMERG "  page->mapping = %p\n", page->mapping);
+			print_symbol (KERN_EMERG "  vma->vm_ops = %s\n", (unsigned long)vma->vm_ops);
+			if (vma->vm_ops)
+				print_symbol (KERN_EMERG "  vma->vm_ops->nopage = %s\n", (unsigned long)vma->vm_ops->nopage);
+			if (vma->vm_file && vma->vm_file->f_op)
+				print_symbol (KERN_EMERG "  vma->vm_file->f_op->mmap = %s\n", (unsigned long)vma->vm_file->f_op->mmap);
 			BUG();
 		}
 
@@ -679,7 +686,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 		dec_mm_counter(mm, file_rss);
 
 
-	page_remove_rmap(page);
+	page_remove_rmap(page, vma);
 	page_cache_release(page);
 
 out_unmap:
@@ -769,7 +776,7 @@ static void try_to_unmap_cluster(unsigned long cursor,
 		if (pte_dirty(pteval))
 			set_page_dirty(page);
 
-		page_remove_rmap(page);
+		page_remove_rmap(page, vma);
 		page_cache_release(page);
 		dec_mm_counter(mm, file_rss);
 		(*mapcount)--;