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 2556BC00140 for ; Mon, 15 Aug 2022 07:41:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241242AbiHOHk6 (ORCPT ); Mon, 15 Aug 2022 03:40:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42182 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241492AbiHOHks (ORCPT ); Mon, 15 Aug 2022 03:40:48 -0400 Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A765960C6 for ; Mon, 15 Aug 2022 00:40:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1660549246; x=1692085246; h=from:to:cc:subject:references:date:in-reply-to: message-id:mime-version; bh=yOnnsZdwTjhOV4GiTvcT6QmvdCBeALTyO14/f1k1UWk=; b=m7rCS6xujoFPPosWNdVp7cjS1w0LWwn5tssqATb0oMnMMOepIL/W1WTw Tm96cpPmA2bVfRGNylqwRMYKCkDhrRZTGIU+bW3QFmTWblc2AIlAaCArE IMeTowVXLkOm4xBKzMuAHY/osu+X+CIItovarX/Dqo9o+gne6yE+112HE +iF2Pke2JF3VKx78JNItRGRi5j/eq33ABGzYqMGFbNObK9o6P+P4DWge3 Lxw0tQ3BfRNtndXgcMCHjf8v2BsS9eQJdU9TjK5C2hbIxKGzcnr9oUq5X 1HW0w4kaOssTKIMNoPSQjMBG7ekO4vHDYCDI+prhJva59F4ZCYwK9de6J A==; X-IronPort-AV: E=McAfee;i="6400,9594,10439"; a="293181715" X-IronPort-AV: E=Sophos;i="5.93,237,1654585200"; d="scan'208";a="293181715" Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Aug 2022 00:40:29 -0700 X-IronPort-AV: E=Sophos;i="5.93,237,1654585200"; d="scan'208";a="582796154" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by orsmga006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Aug 2022 00:40:26 -0700 From: "Huang, Ying" To: Haiyue Wang Cc: , , , , , , , , Subject: Re: [PATCH v5 1/2] mm: migration: fix the FOLL_GET failure on following huge page References: <20220812084921.409142-1-haiyue.wang@intel.com> <20220815070240.470469-1-haiyue.wang@intel.com> <20220815070240.470469-2-haiyue.wang@intel.com> Date: Mon, 15 Aug 2022 15:40:17 +0800 In-Reply-To: <20220815070240.470469-2-haiyue.wang@intel.com> (Haiyue Wang's message of "Mon, 15 Aug 2022 15:02:39 +0800") Message-ID: <87k07ac5um.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Haiyue Wang writes: > 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 > 2. follow_huge_addr() in arch/ia64/mm/hugetlbpage.c > It will cause WARN_ON_ONCE for FOLL_GET. > 3. follow_huge_pgd() in mm/hugetlb.c > > 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. > > Fixes: 4cd614841c06 ("mm: migration: fix possible do_pages_stat_array racing with memory offline") > Signed-off-by: Haiyue Wang LGTM, Thanks! Reviewed-by: "Huang, Ying" > --- > mm/migrate.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 6a1597c92261..581dfaad9257 100644 > --- 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; > }