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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 CDF2EC433E0 for ; Sat, 30 May 2020 20:41:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A3BBE20801 for ; Sat, 30 May 2020 20:41:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="HZvQiU2Y" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729346AbgE3Ulh (ORCPT ); Sat, 30 May 2020 16:41:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40040 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726211AbgE3Ulh (ORCPT ); Sat, 30 May 2020 16:41:37 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2DF5BC03E969; Sat, 30 May 2020 13:41:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=4OdrZK2pGyMVHZP9dBAVdzAWc40dh9XQscP29VyVrvM=; b=HZvQiU2YlUtBkyi6j0X0sBvcK6 YZbb6RElwJlDvQSoI8EnGgMdqBHoihEOfco2ouCjUP4Lrt9K1yHxN8OR5Caaio7SnY2tGtjpu2vng jr1IQnGoevyNcal8I/kgEqEGTu3l+Zwlh5LVZwcZgiHGb4WD6ut/ABzyv8M2MhE68B0QNvidpnC3Q 2Lj81yDjMRBVamW438WZSQXqIyI6NJY97hDAeLt7m7VQQfHf4EELlTmQSzzKspRVXWPOK0cCOwljZ sJ9Nep2Dn0XzCi79koJwJFZzSkEGkTSq4HO0sQ6syXZ7aNRGYBeUxnVBXkgbEbKIIudGg/NB/2i+7 XqHaEaWg==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jf8IO-0000XW-Qx; Sat, 30 May 2020 20:41:32 +0000 Date: Sat, 30 May 2020 13:41:32 -0700 From: Matthew Wilcox To: Eric Biggers Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, stable@vger.kernel.org, Al Viro , Daniel Rosenberg , Gabriel Krisman Bertazi Subject: Re: [PATCH] ext4: avoid utf8_strncasecmp() with unstable name Message-ID: <20200530204132.GE19604@bombadil.infradead.org> References: <20200530060216.221456-1-ebiggers@kernel.org> <20200530171814.GD19604@bombadil.infradead.org> <20200530173547.GA12299@sol.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200530173547.GA12299@sol.localdomain> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Sat, May 30, 2020 at 10:35:47AM -0700, Eric Biggers wrote: > On Sat, May 30, 2020 at 10:18:14AM -0700, Matthew Wilcox wrote: > > On Fri, May 29, 2020 at 11:02:16PM -0700, Eric Biggers wrote: > > > + if (len <= DNAME_INLINE_LEN - 1) { > > > + unsigned int i; > > > + > > > + for (i = 0; i < len; i++) > > > + strbuf[i] = READ_ONCE(str[i]); > > > + strbuf[len] = 0; > > > > This READ_ONCE is going to force the compiler to use byte accesses. > > What's wrong with using a plain memcpy()? > > > > It's undefined behavior when the source can be concurrently modified. > > Compilers can assume that it's not, and remove the memcpy() (instead just using > the source data directly) if they can prove that the destination array is never > modified again before it goes out of scope. > > Do you have any suggestions that don't involve undefined behavior? void *memcpy_unsafe(void *dst, volatile void *src, __kernel_size_t); It can just call memcpy() of course, but the compiler can't reason about this function because it's not a stdlib function.