From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1173583AbdDXRag (ORCPT ); Mon, 24 Apr 2017 13:30:36 -0400 Received: from mail-wr0-f194.google.com ([209.85.128.194]:33704 "EHLO mail-wr0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758745AbdDXRaZ (ORCPT ); Mon, 24 Apr 2017 13:30:25 -0400 Date: Mon, 24 Apr 2017 20:30:21 +0300 From: "Kirill A. Shutemov" To: Dan Williams Cc: Linux MM , Catalin Marinas , "Aneesh Kumar K.V" , Steve Capper , Thomas Gleixner , Peter Zijlstra , Linux Kernel Mailing List , Ingo Molnar , Andrew Morton , "Kirill A. Shutemov" , "H. Peter Anvin" , Dave Hansen , Borislav Petkov , Rik van Riel , Dann Frazier , Linus Torvalds , Michal Hocko , linux-tip-commits@vger.kernel.org Subject: Re: get_zone_device_page() in get_page() and page_cache_get_speculative() Message-ID: <20170424173021.ayj3hslvfrrgrie7@node.shutemov.name> References: <20170423233125.nehmgtzldgi25niy@node.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170306 (1.8.0) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 24, 2017 at 10:23:59AM -0700, Dan Williams wrote: > On Sun, Apr 23, 2017 at 4:31 PM, Kirill A. Shutemov > wrote: > > On Thu, Apr 20, 2017 at 02:46:51PM -0700, Dan Williams wrote: > >> On Sat, Mar 18, 2017 at 2:52 AM, tip-bot for Kirill A. Shutemov > >> wrote: > >> > Commit-ID: 2947ba054a4dabbd82848728d765346886050029 > >> > Gitweb: http://git.kernel.org/tip/2947ba054a4dabbd82848728d765346886050029 > >> > Author: Kirill A. Shutemov > >> > AuthorDate: Fri, 17 Mar 2017 00:39:06 +0300 > >> > Committer: Ingo Molnar > >> > CommitDate: Sat, 18 Mar 2017 09:48:03 +0100 > >> > > >> > x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation > >> > > >> > This patch provides all required callbacks required by the generic > >> > get_user_pages_fast() code and switches x86 over - and removes > >> > the platform specific implementation. > >> > > >> > Signed-off-by: Kirill A. Shutemov > >> > Cc: Andrew Morton > >> > Cc: Aneesh Kumar K . V > >> > Cc: Borislav Petkov > >> > Cc: Catalin Marinas > >> > Cc: Dann Frazier > >> > Cc: Dave Hansen > >> > Cc: H. Peter Anvin > >> > Cc: Linus Torvalds > >> > Cc: Peter Zijlstra > >> > Cc: Rik van Riel > >> > Cc: Steve Capper > >> > Cc: Thomas Gleixner > >> > Cc: linux-arch@vger.kernel.org > >> > Cc: linux-mm@kvack.org > >> > Link: http://lkml.kernel.org/r/20170316213906.89528-1-kirill.shutemov@linux.intel.com > >> > [ Minor readability edits. ] > >> > Signed-off-by: Ingo Molnar > >> > >> I'm still trying to spot the bug, but bisect points to this patch as > >> the point at which my unit tests start failing with the following > >> signature: > >> > >> [ 35.423841] WARNING: CPU: 8 PID: 245 at lib/percpu-refcount.c:155 > >> percpu_ref_switch_to_atomic_rcu+0x1f5/0x200 > > > > Okay, I've tracked it down. The issue is triggered by replacment > > get_page() with page_cache_get_speculative(). > > > > page_cache_get_speculative() doesn't have get_zone_device_page(). :-| > > > > And I think it's your bug, Dan: it's wrong to have > > get_/put_zone_device_page() in get_/put_page(). I must be handled by > > page_ref_* machinery to catch all cases where we manipulate with page > > refcount. > > The page_ref conversion landed in 4.6 *after* the ZONE_DEVICE > implementation that landed in 4.5, so there was a missed conversion of > the zone-device reference counting to page_ref. Fair enough. But get_page_unless_zero() definitely predates ZONE_DEVICE. :) -- Kirill A. Shutemov