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 X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BAFE3C10DCE for ; Fri, 13 Mar 2020 03:57:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 81AE9206E2 for ; Fri, 13 Mar 2020 03:57:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584071864; bh=w+ZZsFzaN02z4LjftM7wNgCAMWF+UZWUmlO2OdveGgo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=Q6WZevb0yuDO1d8rCklAUd84HuWtQbPmH4vVo3eCvxZ6ALD/DGPNfGLjE/Mb9JAFK WRUMOtQAdsLPIdgz41xZ9Te0nnQdPTHNCus+4Oiq69D5b8KYvLu0HzIstJv+Ym5Nc5 1dTwVPwzyl0KqubS9T5pMimYuqZ1EMkUOGrxqJj8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726464AbgCMD5n (ORCPT ); Thu, 12 Mar 2020 23:57:43 -0400 Received: from mail.kernel.org ([198.145.29.99]:38046 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726328AbgCMD5n (ORCPT ); Thu, 12 Mar 2020 23:57:43 -0400 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7A9B72072F; Fri, 13 Mar 2020 03:57:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584071862; bh=w+ZZsFzaN02z4LjftM7wNgCAMWF+UZWUmlO2OdveGgo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=igO6WyhXDpgdYdsk1Lro4MZ9Kz09lJRzqTA9EBGjn+aZktwUnpRiZ9PNyUYo98e65 ymzJ0f1po2wfMTl+Xp4p7XbDObPJ8SO5dXdTZEk3Ss9M+2rWfMhSb5TX9LZ+4jOZet WA2j+tJuJdOcvRRUh/seQTOBB1Smmxy5aLYSDRMg= Date: Thu, 12 Mar 2020 20:57:41 -0700 From: Andrew Morton To: Souptick Joarder Cc: =?ISO-8859-1?Q?J=E9r=F4me?= Glisse , Linux-MM , linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/hmm.c : Remove additional check for lockdep_assert_held() Message-Id: <20200312205741.e97a201037103bbf51e1df40@linux-foundation.org> In-Reply-To: References: <1584065460-22205-1-git-send-email-jrdr.linux@gmail.com> <20200312195850.29693d4e55ec27ae11443c0f@linux-foundation.org> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 13 Mar 2020 09:17:22 +0530 Souptick Joarder wrote: > On Fri, Mar 13, 2020 at 8:28 AM Andrew Morton wrote: > > > > On Fri, 13 Mar 2020 07:41:00 +0530 Souptick Joarder wrote: > > > > > walk_page_range() already has a check for lockdep_assert_held(). > > > So additional check for lockdep_assert_held() can be removed from > > > hmm_range_fault(). > > > > > > ... > > > > > > --- a/mm/hmm.c > > > +++ b/mm/hmm.c > > > @@ -681,7 +681,6 @@ long hmm_range_fault(struct hmm_range *range, unsigned int flags) > > > struct mm_struct *mm = range->notifier->mm; > > > int ret; > > > > > > - lockdep_assert_held(&mm->mmap_sem); > > > > > > do { > > > /* If range is no longer valid force retry. */ > > > > It isn't very obvious that hmm_range_fault() is and will only be called > > from walk_page_range() (is it?) > > > > Sorry Andrew, didn't get this part ? > * hmm_range_fault() is and will only be called > from walk_page_range() (is it?) * The patch assumes that hmm_range_fault() will only ever be called via walk_page_range(). How do we know this is the case? And that it always will be the case?