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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id A1A9AC433FE for ; Tue, 18 Oct 2022 19:58:34 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EC6AB6B0072; Tue, 18 Oct 2022 15:58:33 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E76A86B0075; Tue, 18 Oct 2022 15:58:33 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D3E366B0078; Tue, 18 Oct 2022 15:58:33 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id C18B36B0072 for ; Tue, 18 Oct 2022 15:58:33 -0400 (EDT) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id A1FE4403B8 for ; Tue, 18 Oct 2022 19:58:33 +0000 (UTC) X-FDA: 80035132506.16.0C391F3 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf12.hostedemail.com (Postfix) with ESMTP id 3A5BE40037 for ; Tue, 18 Oct 2022 19:58:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=HP274ajX/YSD61RLLeUZGfhgXsGfDEm1d9mPkitVp+k=; b=PNOFcouPCbX/LxUMKNmdVOpXyo NQFCrDVuwF++hr9EDL2AXdDf1CmKyI+MtomwifRsj+8xr9zf4z5IlHK3MtFw7R6vpChlPRYg7M+Lw 6k/Q2YWYVrGxJjZb2pROplMuZDnMX2S62yf+9kKhXTb6Vr1JfEXq+HWAI0Mjk5Jtv+TG/z26+xRJM zbJdhGwOJw1UiJN8j1h57vkXQq/WMY0jP3bYYSCGwX0VRxseP7APRwTF/AZle74fZP+eFU+67D0ak w7Eq/+rWKPFOb2YyuZW347guGk3eYN4eBiJNoUf29E8XB7RlL/XwxWifbdnSy/io5pGNvUo8fPPaV zfGb+8Gg==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1oksjM-00Ayvg-5Q; Tue, 18 Oct 2022 19:58:28 +0000 Date: Tue, 18 Oct 2022 20:58:28 +0100 From: Matthew Wilcox To: David Hildenbrand Cc: Liam Howlett , "maple-tree@lists.infradead.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Andrew Morton , Liu Zixian , Jason Gunthorpe , Mark Rutland Subject: Re: [PATCH] mm/mmap: Fix MAP_FIXED address return on VMA merge Message-ID: References: <20221018191613.4133459-1-Liam.Howlett@oracle.com> <3da4244a-5a1b-cf34-bf5c-22c199b15cb6@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3da4244a-5a1b-cf34-bf5c-22c199b15cb6@redhat.com> ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=PNOFcouP; spf=none (imf12.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666123113; a=rsa-sha256; cv=none; b=ZrBLianJ82QJfoUOuKKpGkHtY+FH+ivZCl2vIPoIvroLdTI1vO3zU92hTbBnBsTAto5UM/ 5cxsPxBfzOGJl+mSZXRvS/7efWUg8ksDGQwdwxnDtCEVvr+1NiF4mcoTfUpydMXA+k34WW u9Csi1GGzmFBBttb6z+oCjuLbX0zxF0= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666123113; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=HP274ajX/YSD61RLLeUZGfhgXsGfDEm1d9mPkitVp+k=; b=sKS9qJy0fFLYb3OBb8a6gJc60TXy2ZgQw4am7bXqh1JsKPjNlGoQ8bu7brj/VCiWlRwLxx VG5AUauZERpvbb9Orxvcw1d5gMRyE2CNTiElEdBNx0TbYk47Ii4UqXGVujOcPvU48hlPGX WjNllut6DMv0+BjvsypALrWIE95HphU= X-Stat-Signature: p9594bsh6757s1xc1n4wq3fyadx4zinr X-Rspamd-Queue-Id: 3A5BE40037 Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=PNOFcouP; spf=none (imf12.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1666123112-528125 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Oct 18, 2022 at 09:27:11PM +0200, David Hildenbrand wrote: > > + if (WARN_ON((addr != vma->vm_start))) { > > + error = -EINVAL; > > + goto close_and_free_vma; > > + } > > If this is something that user space can trigger, WARN_* is the wrong > choice. But what I understand from the comment change is that this must not > happen at that point unless there is a real issue. It's something that a device driver can trigger. So if userspace calls mmap(MAP_FIXED) and the driver decides to overwrite the vma->vm_start, it'll trigger. I think WARN_ON() is the right choice. > Why not "if (WARN_ON_ONCE)" ? Because by it's nature it's not going to trigger a bajillion times in quick succession.