The patch titled Subject: THP: fix comment about memory barrier has been added to the -mm tree. Its filename is thp-fix-comment-about-memory-barrier.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Minchan Kim <minchan@xxxxxxxxxx> Subject: THP: fix comment about memory barrier Now, 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 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 0ed361dec ("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@xxxxxxxxxx> Acked-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> Acked-by: David Rientjes <rientjes@xxxxxxxxxx> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/huge_memory.c | 11 +++++------ mm/memory.c | 5 +++++ 2 files changed, 10 insertions(+), 6 deletions(-) diff -puN mm/huge_memory.c~thp-fix-comment-about-memory-barrier mm/huge_memory.c --- a/mm/huge_memory.c~thp-fix-comment-about-memory-barrier +++ a/mm/huge_memory.c @@ -713,6 +713,11 @@ static int __do_huge_pmd_anonymous_page( 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. + */ __SetPageUptodate(page); spin_lock(&mm->page_table_lock); @@ -724,12 +729,6 @@ static int __do_huge_pmd_anonymous_page( } 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 -puN mm/memory.c~thp-fix-comment-about-memory-barrier mm/memory.c --- a/mm/memory.c~thp-fix-comment-about-memory-barrier +++ a/mm/memory.c @@ -3196,6 +3196,11 @@ static int do_anonymous_page(struct mm_s 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)) _ Patches currently in -mm which might be from minchan@xxxxxxxxxx are linux-next.patch mm-frontswap-lazy-initialization-to-allow-tmem-backends-to-build-run-as-modules.patch frontswap-make-frontswap_init-use-a-pointer-for-the-ops.patch mm-frontswap-cleanup-code.patch frontswap-get-rid-of-swap_lock-dependency.patch mm-cleancache-lazy-initialization-to-allow-tmem-backends-to-build-run-as-modules.patch cleancache-make-cleancache_init-use-a-pointer-for-the-ops.patch mm-cleancache-clean-up-cleancache_enabled.patch xen-tmem-enable-xen-tmem-shim-to-be-built-loaded-as-a-module.patch xen-tmem-enable-xen-tmem-shim-to-be-built-loaded-as-a-module-fix.patch zcache-tmem-better-error-checking-on-frontswap_register_ops-return-value.patch staging-zcache-enable-ramster-to-be-built-loaded-as-a-module.patch staging-zcache-enable-zcache-to-be-built-loaded-as-a-module.patch mm-introduce-free_highmem_page-helper-to-free-highmem-pages-into-buddy-system.patch thp-fix-comment-about-memory-barrier.patch mm-add-vm-event-counters-for-balloon-pages-compaction.patch block-aio-batch-completion-for-bios-kiocbs.patch debugging-keep-track-of-page-owners-fix-2.patch debugging-keep-track-of-page-owners-fix-2-fix.patch debugging-keep-track-of-page-owners-fix-2-fix-fix.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html