path: root/mm/memory.c
diff options
authorMinchan Kim <>2013-04-29 15:08:15 -0700
committerLinus Torvalds <>2013-04-29 15:54:37 -0700
commit52f37629fd3c7b24e1e6c125e665454cd7ac1acb (patch)
tree8dd4a3b22cbb4d89f2b7e686189e8ced3319dcea /mm/memory.c
parentf1cb08798e2497238b28f377bd131426f0b9835d (diff)
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: 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 <>
Diffstat (limited to 'mm/memory.c')
1 files changed, 5 insertions, 0 deletions
diff --git a/mm/memory.c b/mm/memory.c
index ba94dec5b259..f7a1fba85d14 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.
+ */
if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL))