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=-4.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 3031CC48BDF for ; Thu, 24 Jun 2021 12:22:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0F12A613EE for ; Thu, 24 Jun 2021 12:22:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230136AbhFXMY1 (ORCPT ); Thu, 24 Jun 2021 08:24:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43342 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229573AbhFXMY0 (ORCPT ); Thu, 24 Jun 2021 08:24:26 -0400 Received: from mail-wm1-x32d.google.com (mail-wm1-x32d.google.com [IPv6:2a00:1450:4864:20::32d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B47CBC061574; Thu, 24 Jun 2021 05:22:07 -0700 (PDT) Received: by mail-wm1-x32d.google.com with SMTP id t11-20020a1cc30b0000b02901cec841b6a0so4768826wmf.0; Thu, 24 Jun 2021 05:22:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=to:cc:references:from:subject:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=hLhsABdAx0Xsmj9MOPP942v7TyxXPvs6X5/ccjBOw5Y=; b=pkhTpV144GXJgDUoTud8USOZtxEdfdJ94B77TJTnoND95iep1qiFVbY67v0fPB2Jan x/lFWEKooGEriqcLK6KrQEwIClsPtQQMAjGoIMCPsNg2PDuJ1R2uVIVUMXfFTdTdVQzD WKr5KI3vLwJskMCRHsZ4SZkizviIREUZbSOr9/5LGdIMBAkr4ir93bsp/dKpU/q+SZaX dafF2SNV0iL+mHtUbc/sMwa96zBBytHB0OefJOAAxCLdRPOW7LJ19QFkiJCC1YlGckIg UfeLcuJg4x2yfp57hf/9c++fv3hroMpGl+iM1KfXMyYzQcOYAdW7CfsUvCiI0k/EjpUx 2YRQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:to:cc:references:from:subject:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=hLhsABdAx0Xsmj9MOPP942v7TyxXPvs6X5/ccjBOw5Y=; b=nt/Ott+dVZvwMD0MgkY+9mJdLBuy3u13dBio6LLq2tM4A2XjO40mmYr47MqFYMPGLG JmM/vERUE2sOeLkcolbwjHb3+2++vTLZ0Mel9BJL1CojGca3f8sAc7AcyClmDuH0meAZ mf1smaF8cvcdBxx6K+EJY2swnDqh1aNs48G8r5upRLv6KDcBZUrh8AgEoWg4hWNi8YJ3 X5TC2vjtA2P2Tb4kmh/kuImZkzAQNjQvjAgLa3Rua/+AwrNmmvyrVa4w1oh3yV2nIfgs fa4urvmDndOGVfrvH/+lEWrZofxEEzNQ8MKz2Pgxc97DLDK5aCmpQ5A5NfAEOlfiXcil qrTg== X-Gm-Message-State: AOAM532kptuu1wAAqIjMJ34+JoyD6IZ4gT1K/Ndzgeqr3bVTQLr8M5JP Xi60D+o631ZsyzSPYMnatY9Q3cz3B4VN8LbC X-Google-Smtp-Source: ABdhPJxzRgctJn6NygdWrLjommXSXDqvFNrRc5koTW0b7Ebf5x/fL75XidgTxFG+NkbSTWlYKWxIOA== X-Received: by 2002:a05:600c:2c4a:: with SMTP id r10mr3977500wmg.162.1624537325951; Thu, 24 Jun 2021 05:22:05 -0700 (PDT) Received: from [192.168.8.197] ([148.252.132.93]) by smtp.gmail.com with ESMTPSA id i9sm2953873wrn.13.2021.06.24.05.22.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 24 Jun 2021 05:22:05 -0700 (PDT) To: Dmitry Kadashev Cc: Jens Axboe , Alexander Viro , Christian Brauner , linux-fsdevel@vger.kernel.org, io-uring References: <20210603051836.2614535-1-dkadashev@gmail.com> <20210603051836.2614535-3-dkadashev@gmail.com> <4c0344d8-6725-84a6-b0a8-271587d7e604@gmail.com> <15a9d84b-61df-e2af-0c79-75b54d4bae8f@gmail.com> From: Pavel Begunkov Subject: Re: [PATCH v5 02/10] io_uring: add support for IORING_OP_MKDIRAT Message-ID: Date: Thu, 24 Jun 2021 13:21:49 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 6/24/21 12:11 PM, Dmitry Kadashev wrote: > On Wed, Jun 23, 2021 at 6:54 PM Pavel Begunkov wrote: >> >> On 6/23/21 7:41 AM, Dmitry Kadashev wrote: >>> I'd imagine READ_ONCE is to be used in those checks though, isn't it? Some of >>> the existing checks like this lack it too btw. I suppose I can fix those in a >>> separate commit if that makes sense. >> >> When we really use a field there should be a READ_ONCE(), >> but I wouldn't care about those we check for compatibility >> reasons, but that's only my opinion. > > I'm not sure how the compatibility check reads are special. The code is > either correct or not. If a compatibility check has correctness problems > then it's pretty much as bad as any other part of the code having such > problems, no? If it reads and verifies a values first, e.g. index into some internal array, and then compiler plays a joke and reloads it, we might be absolutely screwed expecting 'segfaults', kernel data leakages and all the fun stuff. If that's a compatibility check, whether it's loaded earlier or later, or whatever, it's not a big deal, the userspace can in any case change the memory at any moment it wishes, even tightly around the moment we're reading it. > That said, I'll just go ahead and use the approach that the rest of the > code (or rather most of it) uses (no READ_ONCE). If it needs fixing then > the whole bunch can probably be fixed in one go (either a single patch > or a series). > > Thanks for your help, Pavel! > -- Pavel Begunkov