From 44fc80573cc760a7154f41fd0a958ee10eba1a81 Mon Sep 17 00:00:00 2001 From: David Rientjes Date: Thu, 12 Mar 2015 16:25:54 -0700 Subject: [PATCH] mm, hugetlb: close race when setting PageTail for gigantic pages Now that gigantic pages are dynamically allocatable, care must be taken to ensure that p->first_page is valid before setting PageTail. If this isn't done, then it is possible to race and have compound_head() return NULL. Signed-off-by: David Rientjes Acked-by: Davidlohr Bueso Cc: Luiz Capitulino Cc: Joonsoo Kim Acked-by: Hillf Danton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/hugetlb.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 0a9ac6c26832..c41b2a0ee273 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -917,7 +917,6 @@ static void prep_compound_gigantic_page(struct page *page, unsigned long order) __SetPageHead(page); __ClearPageReserved(page); for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) { - __SetPageTail(p); /* * For gigantic hugepages allocated through bootmem at * boot, it's safer to be consistent with the not-gigantic @@ -933,6 +932,9 @@ static void prep_compound_gigantic_page(struct page *page, unsigned long order) __ClearPageReserved(p); set_page_count(p, 0); p->first_page = page; + /* Make sure p->first_page is always valid for PageTail() */ + smp_wmb(); + __SetPageTail(p); } }