[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>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 7c7d03dbf73dc6953283553cb17ef0ee76ddab94..1d709ff528e1e91cd9bbbf086f119c5d4ba3154a 100644 (file)
--- 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,