Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752544AbaFFXQ5 (ORCPT ); Fri, 6 Jun 2014 19:16:57 -0400 Received: from mail-vc0-f181.google.com ([209.85.220.181]:60270 "EHLO mail-vc0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752183AbaFFXQ4 (ORCPT ); Fri, 6 Jun 2014 19:16:56 -0400 MIME-Version: 1.0 In-Reply-To: References: <20140603042121.GA27177@redhat.com> <538F121E.9020100@oracle.com> Date: Fri, 6 Jun 2014 16:16:55 -0700 X-Google-Sender-Auth: uYhXv7SOq4P8DcAaHCKU6kI3-Ig Message-ID: Subject: Re: 3.15-rc8 mm/filemap.c:202 BUG From: Linus Torvalds To: Hugh Dickins Cc: Sasha Levin , Andrew Morton , "Kirill A. Shutemov" , Konstantin Khlebnikov , Dave Jones , "linux-mm@kvack.org" , Linux Kernel Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 6, 2014 at 4:05 PM, Hugh Dickins wrote: > > [PATCH] mm: entry = ACCESS_ONCE(*pte) in handle_pte_fault > > Use ACCESS_ONCE() in handle_pte_fault() when getting the entry or orig_pte > upon which all subsequent decisions and pte_same() tests will be made. > > I have no evidence that its lack is responsible for the mm/filemap.c:202 > BUG_ON(page_mapped(page)) in __delete_from_page_cache() found by trinity, > and I am not optimistic that it will fix it. But I have found no other > explanation, and ACCESS_ONCE() here will surely not hurt. The patch looks obviously correct to me, although like you, I have no real reason to believe it really fixes anything. But we definitely should just load it once, since it's very much an optimistic load done before we take the real lock and re-compare. I'm somewhat dubious whether it actually would change code generation - it doesn't change anything with the test-configuration I tried with - but it's unquestionably a good patch. And hey, maybe some configurations have sufficiently different code generation that gcc actually _can_ sometimes do reloads, perhaps explaining why some people see problems. So it's certainly worth testing even if it doesn't make any change to code generation with *my* compiler and config.. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/