[PATCH] enforce proper tlb flush in unmap_hugepage_range

Spotted by Hugh that hugetlb page is free'ed back to global pool before
performing any TLB flush in unmap_hugepage_range().  This potentially allow
threads to abuse free-alloc race condition.

The generic tlb gather code is unsuitable to use by hugetlb, I just open
coded a page gathering list and delayed put_page until tlb flush is
performed.

Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>
Acked-by: William Irwin <wli@holomorphy.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 7c7d03dbf73d..1d709ff528e1 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -364,6 +364,8 @@ void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
         pte_t *ptep;
         pte_t pte;
         struct page *page;
+        struct page *tmp;
+        LIST_HEAD(page_list);
 
         WARN_ON(!is_vm_hugetlb_page(vma));
         BUG_ON(start & ~HPAGE_MASK);
@@ -384,12 +386,16 @@ void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
                         continue;
 
                 page = pte_page(pte);
-                put_page(page);
+                list_add(&page->lru, &page_list);
                 add_mm_counter(mm, file_rss, (int) -(HPAGE_SIZE / PAGE_SIZE));
         }
 
         spin_unlock(&mm->page_table_lock);
         flush_tlb_range(vma, start, end);
+        list_for_each_entry_safe(page, tmp, &page_list, lru) {
+                list_del(&page->lru);
+                put_page(page);
+        }
 }
 
 static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,