From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753903AbdFMOGn (ORCPT ); Tue, 13 Jun 2017 10:06:43 -0400 Received: from mga05.intel.com ([192.55.52.43]:11978 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753389AbdFMOGk (ORCPT ); Tue, 13 Jun 2017 10:06:40 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.39,338,1493708400"; d="scan'208";a="980264443" Date: Tue, 13 Jun 2017 17:06:01 +0300 From: "Kirill A. Shutemov" To: Will Deacon Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, mark.rutland@arm.com, akpm@linux-foundation.org, Punit.Agrawal@arm.com, mgorman@suse.de, steve.capper@arm.com, vbabka@suse.cz Subject: Re: [PATCH v2 2/3] mm/page_ref: Ensure page_ref_unfreeze is ordered against prior accesses Message-ID: <20170613140600.2orf4miov5gd3qqb@black.fi.intel.com> References: <1497349722-6731-1-git-send-email-will.deacon@arm.com> <1497349722-6731-3-git-send-email-will.deacon@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1497349722-6731-3-git-send-email-will.deacon@arm.com> User-Agent: NeoMutt/20161126 (1.7.0) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 13, 2017 at 11:28:41AM +0100, Will Deacon wrote: > 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(); Don't we want some comment here? Otherwise: Acked-by: Kirill A. Shutemov -- Kirill A. Shutemov