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 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 DCEBEC4724C for ; Thu, 30 Apr 2020 21:23:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AADFB21775 for ; Thu, 30 Apr 2020 21:23:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588281793; bh=64VkPdoiN0OePS1AJNJImnN0TBSj5RZkl5WHr7pH2zc=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=vcuhNIHeI+VULIXmlS/cXnBt3nhuIT4fcxDxh6528pp98xKwdymE8E7xjxRvhZK00 0k3pWxFPdyR3JKH8kH1Q7sY/SNUGPBG5tbLxPBoI/ijwSUJy9xoUAWD3fxFNlG5PxI OuyQdSmRN/NAspfsW069ypmFDL0uHse5FajDVhy8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727044AbgD3VXM (ORCPT ); Thu, 30 Apr 2020 17:23:12 -0400 Received: from mail.kernel.org ([198.145.29.99]:40378 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726483AbgD3VXM (ORCPT ); Thu, 30 Apr 2020 17:23:12 -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 302412166E; Thu, 30 Apr 2020 21:23:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588281792; bh=64VkPdoiN0OePS1AJNJImnN0TBSj5RZkl5WHr7pH2zc=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=QAitjNdyFZAKZsl9w/HSamjjGQ43tPG20k8YV2BhA6BAzLoL8vXNaWoF9UMgfQlOl pz18SKiCyaRhywDfyy1jCV0/LK15E/q4uBqFP8Tx1y3f51UjeysrNXGr/bRGdaLgLN gix2QWqIln1sTlUAN7qwXwkBNh3ycqNJqvImuaK4= Date: Thu, 30 Apr 2020 14:23:11 -0700 From: Andrew Morton To: Souptick Joarder Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/gup.c: Handle error at earliest for incorrect nr_pages value Message-Id: <20200430142311.091b82235141ca47b9c6475a@linux-foundation.org> In-Reply-To: <1588277518-21425-1-git-send-email-jrdr.linux@gmail.com> References: <1588277518-21425-1-git-send-email-jrdr.linux@gmail.com> 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, 1 May 2020 01:41:58 +0530 Souptick Joarder wrote: > As per documentation, pin_user_pages_fast() & get_user_pages_fast() > will return 0, if nr_pages <= 0. But this can be figure out only after > going inside the internal_get_user_pages_fast(). > > This can be handled early. Adding a check for the same. Calling get_user_pages() for (nrpages <= 0) is a nonsensical thing to do so it isn't a thing we should care to optimize. Adding new checks will actually slow down the use cases which we *do* care about. And it adds more code.