[PATCH] mm: rmap with inner ptlock

rmap's page_check_address descend without page_table_lock.  First just
pte_offset_map in case there's no pte present worth locking for, then take
page_table_lock for the full check, and pass ptl back to caller in the same
style as pte_offset_map_lock.  __xip_unmap, page_referenced_one and
try_to_unmap_one use pte_unmap_unlock.  try_to_unmap_cluster also.

page_check_address reformatted to avoid progressive indentation.  No use is
made of its one error code, return NULL when it fails.

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

mm/filemap_xip.c

@@ -174,6 +174,7 @@ __xip_unmap (struct address_space * mapping,
 	unsigned long address;
 	pte_t *pte;
 	pte_t pteval;
+	spinlock_t *ptl;
 	struct page *page;
 
 	spin_lock(&mapping->i_mmap_lock);
@@ -183,20 +184,15 @@ __xip_unmap (struct address_space * mapping,
 			((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
 		BUG_ON(address < vma->vm_start || address >= vma->vm_end);
 		page = ZERO_PAGE(address);
-		/*
-		 * We need the page_table_lock to protect us from page faults,
-		 * munmap, fork, etc...
-		 */
-		pte = page_check_address(page, mm, address);
-		if (!IS_ERR(pte)) {
+		pte = page_check_address(page, mm, address, &ptl);
+		if (pte) {
 			/* Nuke the page table entry. */
 			flush_cache_page(vma, address, pte_pfn(*pte));
 			pteval = ptep_clear_flush(vma, address, pte);
 			page_remove_rmap(page);
 			dec_mm_counter(mm, file_rss);
 			BUG_ON(pte_dirty(pteval));
-			pte_unmap(pte);
-			spin_unlock(&mm->page_table_lock);
+			pte_unmap_unlock(pte, ptl);
 			page_cache_release(page);
 		}
 	}