From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753096AbdFMK3R (ORCPT ); Tue, 13 Jun 2017 06:29:17 -0400 Received: from foss.arm.com ([217.140.101.70]:46154 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752156AbdFMK2f (ORCPT ); Tue, 13 Jun 2017 06:28:35 -0400 From: Will Deacon 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, vbabka@suse.cz, Will Deacon Subject: [PATCH v2 2/3] mm/page_ref: Ensure page_ref_unfreeze is ordered against prior accesses Date: Tue, 13 Jun 2017 11:28:41 +0100 Message-Id: <1497349722-6731-3-git-send-email-will.deacon@arm.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1497349722-6731-1-git-send-email-will.deacon@arm.com> References: <1497349722-6731-1-git-send-email-will.deacon@arm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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() 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..1fd71733aa68 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(); atomic_set(&page->_refcount, count); if (page_ref_tracepoint_active(__tracepoint_page_ref_unfreeze)) __page_ref_unfreeze(page, count); -- 2.1.4