path: root/mm
diff options
authorMinchan Kim <minchan@kernel.org>2013-04-29 15:08:15 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-04-29 15:54:37 -0700
commit52f37629fd3c7b24e1e6c125e665454cd7ac1acb (patch)
tree8dd4a3b22cbb4d89f2b7e686189e8ced3319dcea /mm
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: 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 <minchan@kernel.org> Acked-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: David Rientjes <rientjes@google.com> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Hugh Dickins <hughd@google.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
2 files changed, 10 insertions, 6 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index e2f7f5aaaaf..45eaae03062 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -713,6 +713,11 @@ static int __do_huge_pmd_anonymous_page(struct mm_struct *mm,
return VM_FAULT_OOM;
clear_huge_page(page, haddr, HPAGE_PMD_NR);
+ /*
+ * The memory barrier inside __SetPageUptodate makes sure that
+ * clear_huge_page writes become visible before the set_pmd_at()
+ * write.
+ */
@@ -724,12 +729,6 @@ static int __do_huge_pmd_anonymous_page(struct mm_struct *mm,
} else {
pmd_t entry;
entry = mk_huge_pmd(page, vma);
- /*
- * The spinlocking to take the lru_lock inside
- * page_add_new_anon_rmap() acts as a full memory
- * barrier to be sure clear_huge_page writes become
- * visible after the set_pmd_at() write.
- */
page_add_new_anon_rmap(page, vma, haddr);
set_pmd_at(mm, haddr, pmd, entry);
pgtable_trans_huge_deposit(mm, pgtable);
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.
+ */
if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL))