From 52f37629fd3c7b24e1e6c125e665454cd7ac1acb Mon Sep 17 00:00:00 2001 From: Minchan Kim Date: Mon, 29 Apr 2013 15:08:15 -0700 Subject: THP: fix comment about memory barrier Currently the memory barrier in __do_huge_pmd_anonymous_page doesn't work. Because lru_cache_add_lru uses pagevec so it could miss spinlock easily so above rule was broken so user might see inconsistent data. I was not first person who pointed out the problem. Mel and Peter pointed out a few months ago and Peter pointed out further that even spin_lock/unlock can't make sure of it: http://marc.info/?t=134333512700004 In particular: *A = a; LOCK UNLOCK *B = b; may occur as: LOCK, STORE *B, STORE *A, UNLOCK At last, Hugh pointed out that even we don't need memory barrier in there because __SetPageUpdate already have done it from Nick's commit 0ed361dec369 ("mm: fix PageUptodate data race") explicitly. So this patch fixes comment on THP and adds same comment for do_anonymous_page, too because everybody except Hugh was missing that. It means we need a comment about that. Signed-off-by: Minchan Kim Acked-by: Andrea Arcangeli Acked-by: David Rientjes Acked-by: KAMEZAWA Hiroyuki Cc: Mel Gorman Cc: Hugh Dickins Cc: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memory.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'mm/memory.c') diff --git a/mm/memory.c b/mm/memory.c index ba94dec5b25..f7a1fba85d1 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3244,6 +3244,11 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma, page = alloc_zeroed_user_highpage_movable(vma, address); if (!page) goto oom; + /* + * The memory barrier inside __SetPageUptodate makes sure that + * preceeding stores to the page contents become visible before + * the set_pte_at() write. + */ __SetPageUptodate(page); if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL)) -- cgit v1.2.3