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| author | Minchan Kim <minchan@kernel.org> | 2013-04-29 15:08:15 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2013-04-29 15:54:37 -0700 |
| commit | 52f37629fd3c7b24e1e6c125e665454cd7ac1acb (patch) | |
| tree | 8dd4a3b22cbb4d89f2b7e686189e8ced3319dcea /mm/memory.c | |
| parent | f1cb08798e2497238b28f377bd131426f0b9835d (diff) | |
| download | linux-52f37629fd3c7b24e1e6c125e665454cd7ac1acb.tar.gz linux-52f37629fd3c7b24e1e6c125e665454cd7ac1acb.tar.xz | |
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/memory.c')
| -rw-r--r-- | mm/memory.c | 5 |
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. + */ __SetPageUptodate(page); if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL)) |