[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>

1 files changed, 4 insertions, 8 deletions

diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
index 4e74ad60339a..9cf687e4a29a 100644
--- a/mm/filemap_xip.c
+++ b/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);
                 }
         }