From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id F346A6B0279 for ; Tue, 6 Jun 2017 13:58:31 -0400 (EDT) Received: by mail-pf0-f199.google.com with SMTP id c7so11845502pfd.12 for ; Tue, 06 Jun 2017 10:58:31 -0700 (PDT) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id 31si10703492plh.326.2017.06.06.10.58.30 for ; Tue, 06 Jun 2017 10:58:31 -0700 (PDT) From: Will Deacon Subject: [PATCH 2/3] mm/page_ref: Ensure page_ref_unfreeze is ordered against prior accesses Date: Tue, 6 Jun 2017 18:58:35 +0100 Message-Id: <1496771916-28203-3-git-send-email-will.deacon@arm.com> In-Reply-To: <1496771916-28203-1-git-send-email-will.deacon@arm.com> References: <1496771916-28203-1-git-send-email-will.deacon@arm.com> Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: mark.rutland@arm.com, akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, Punit.Agrawal@arm.com, mgorman@suse.de, steve.capper@arm.com, Will Deacon page_ref_freeze and page_ref_unfreeze are designed to be used as a pair, wrapping a critical section where struct pages can be modified without having to worry about consistency for a concurrent fast-GUP. Whilst page_ref_freeze has full barrier semantics due to its use of atomic_cmpxchg, page_ref_unfreeze is implemented using atomic_set, which doesn't provide any barrier semantics and allows the operation to be reordered with respect to page modifications in the critical section. This patch ensures that page_ref_unfreeze is ordered after any critical section updates, by invoking smp_mb__before_atomic() prior to the atomic_set. Cc: "Kirill A. Shutemov" Acked-by: Steve Capper Signed-off-by: Will Deacon --- include/linux/page_ref.h | 1 + 1 file changed, 1 insertion(+) diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h index 610e13271918..74d32d7905cb 100644 --- a/include/linux/page_ref.h +++ b/include/linux/page_ref.h @@ -174,6 +174,7 @@ static inline void page_ref_unfreeze(struct page *page, int count) VM_BUG_ON_PAGE(page_count(page) != 0, page); VM_BUG_ON(count == 0); + smp_mb__before_atomic(); atomic_set(&page->_refcount, count); if (page_ref_tracepoint_active(__tracepoint_page_ref_unfreeze)) __page_ref_unfreeze(page, count); -- 2.1.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org