From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0DB8AC28B2B for ; Wed, 17 Aug 2022 00:58:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237895AbiHQA6o (ORCPT ); Tue, 16 Aug 2022 20:58:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50010 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229911AbiHQA6m (ORCPT ); Tue, 16 Aug 2022 20:58:42 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 382DD77565 for ; Tue, 16 Aug 2022 17:58:41 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id CF0FE6136A for ; Wed, 17 Aug 2022 00:58:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 98865C433C1; Wed, 17 Aug 2022 00:58:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1660697920; bh=C0i0XgffdxbeAl7rnM2KOYPEoBGyXv3zh50EUmQ1DY0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=wDEQ1GWAkUGkZNgxdRt0VUV+SJr7mHVKyZJv7BpUPCugTFKwQI4ri2qMxJ/BGBARM 7WyalY1ZT9FpyQMVmqAXtSQ42YBRlwG7JBfJI6ipiq5F9oQEHKw5hSkOmFNj7JRyYV QdbTCXTsdcbs5oMDwBFAhQaEUNGr8y/GF6sAUGsc= Date: Tue, 16 Aug 2022 17:58:38 -0700 From: Andrew Morton To: Haiyue Wang Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, david@redhat.com, apopple@nvidia.com, linmiaohe@huawei.com, ying.huang@intel.com, songmuchun@bytedance.com, naoya.horiguchi@linux.dev, alex.sierra@amd.com, Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Mike Kravetz Subject: Re: [PATCH v6 1/2] mm: migration: fix the FOLL_GET failure on following huge page Message-Id: <20220816175838.211a1b1e85bc68c439101995@linux-foundation.org> In-Reply-To: <20220816022102.582865-2-haiyue.wang@intel.com> References: <20220812084921.409142-1-haiyue.wang@intel.com> <20220816022102.582865-1-haiyue.wang@intel.com> <20220816022102.582865-2-haiyue.wang@intel.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 16 Aug 2022 10:21:00 +0800 Haiyue Wang wrote: > Not all huge page APIs support FOLL_GET option, so move_pages() syscall > will fail to get the page node information for some huge pages. > > Like x86 on linux 5.19 with 1GB huge page API follow_huge_pud(), it will > return NULL page for FOLL_GET when calling move_pages() syscall with the > NULL 'nodes' parameter, the 'status' parameter has '-2' error in array. > > Note: follow_huge_pud() now supports FOLL_GET in linux 6.0. > Link: https://lore.kernel.org/all/20220714042420.1847125-3-naoya.horiguchi@linux.dev > > But these huge page APIs don't support FOLL_GET: > 1. follow_huge_pud() in arch/s390/mm/hugetlbpage.c Let's tell the s390 maintainers. > 2. follow_huge_addr() in arch/ia64/mm/hugetlbpage.c > It will cause WARN_ON_ONCE for FOLL_GET. ia64 doesn't have maintainers :( Can we come up with something local to arch/ia64 for this? > 3. follow_huge_pgd() in mm/hugetlb.c Hi, Mike. > This is an temporary solution to mitigate the side effect of the race > condition fix by calling follow_page() with FOLL_GET set for huge pages. > > After supporting follow huge page by FOLL_GET is done, this fix can be > reverted safely. > > ... > > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1848,6 +1848,7 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages, > > for (i = 0; i < nr_pages; i++) { > unsigned long addr = (unsigned long)(*pages); > + unsigned int foll_flags = FOLL_DUMP; > struct vm_area_struct *vma; > struct page *page; > int err = -EFAULT; > @@ -1856,8 +1857,12 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages, > if (!vma) > goto set_status; > > + /* Not all huge page follow APIs support 'FOLL_GET' */ > + if (!is_vm_hugetlb_page(vma)) > + foll_flags |= FOLL_GET; > + > /* FOLL_DUMP to ignore special (like zero) pages */ > - page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP); > + page = follow_page(vma, addr, foll_flags); > > err = PTR_ERR(page); > if (IS_ERR(page)) > @@ -1865,7 +1870,8 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages, > > if (page && !is_zone_device_page(page)) { > err = page_to_nid(page); > - put_page(page); > + if (foll_flags & FOLL_GET) > + put_page(page); > } else { > err = -ENOENT; > } I would be better to fix this for real at those three client code sites?