Commit 52f37629fd3c7b24e1e6c125e665454cd7ac1acb
Committed by
Linus Torvalds
Linus Torvalds
1 parent
f1cb08798e
Exists in
master
and in
20 other branches
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>
Showing 2 changed files with 10 additions and 6 deletions Side-by-side Diff
mm/huge_memory.c
| ... | ... | @@ -713,6 +713,11 @@ |
| 713 | 713 | return VM_FAULT_OOM; |
| 714 | 714 | |
| 715 | 715 | clear_huge_page(page, haddr, HPAGE_PMD_NR); |
| 716 | + /* | |
| 717 | + * The memory barrier inside __SetPageUptodate makes sure that | |
| 718 | + * clear_huge_page writes become visible before the set_pmd_at() | |
| 719 | + * write. | |
| 720 | + */ | |
| 716 | 721 | __SetPageUptodate(page); |
| 717 | 722 | |
| 718 | 723 | spin_lock(&mm->page_table_lock); |
| ... | ... | @@ -724,12 +729,6 @@ |
| 724 | 729 | } else { |
| 725 | 730 | pmd_t entry; |
| 726 | 731 | entry = mk_huge_pmd(page, vma); |
| 727 | - /* | |
| 728 | - * The spinlocking to take the lru_lock inside | |
| 729 | - * page_add_new_anon_rmap() acts as a full memory | |
| 730 | - * barrier to be sure clear_huge_page writes become | |
| 731 | - * visible after the set_pmd_at() write. | |
| 732 | - */ | |
| 733 | 732 | page_add_new_anon_rmap(page, vma, haddr); |
| 734 | 733 | set_pmd_at(mm, haddr, pmd, entry); |
| 735 | 734 | pgtable_trans_huge_deposit(mm, pgtable); |
mm/memory.c
| ... | ... | @@ -3244,6 +3244,11 @@ |
| 3244 | 3244 | page = alloc_zeroed_user_highpage_movable(vma, address); |
| 3245 | 3245 | if (!page) |
| 3246 | 3246 | goto oom; |
| 3247 | + /* | |
| 3248 | + * The memory barrier inside __SetPageUptodate makes sure that | |
| 3249 | + * preceeding stores to the page contents become visible before | |
| 3250 | + * the set_pte_at() write. | |
| 3251 | + */ | |
| 3247 | 3252 | __SetPageUptodate(page); |
| 3248 | 3253 | |
| 3249 | 3254 | if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL)) |