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=-1.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS autolearn=unavailable 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 32B52C282D9 for ; Thu, 31 Jan 2019 15:16:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 065AA20863 for ; Thu, 31 Jan 2019 15:16:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="EEuWphwL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726977AbfAaPP4 (ORCPT ); Thu, 31 Jan 2019 10:15:56 -0500 Received: from mail-pl1-f193.google.com ([209.85.214.193]:37461 "EHLO mail-pl1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725787AbfAaPP4 (ORCPT ); Thu, 31 Jan 2019 10:15:56 -0500 Received: by mail-pl1-f193.google.com with SMTP id b5so1614093plr.4; Thu, 31 Jan 2019 07:15:56 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=oTwwCo0HfzAnEhBsPRwUHRSIopGz31NRb8hCyw43RM8=; b=EEuWphwL/36vLGL3FIv8fT5kYFAVQYv1yR85/3xp5a3zpbTWvgMO4RviXhWFXkzJ5q HRQhjvrgExF2f+IdzhslJtPdhcTVoSChUxFufTgvs2ULXKQiEasEg1vfL+kkWjilawLW oL5zWahkc08koy7rYiwflx419QZYtQeJR+2sK53PwAhmQ+WxnT8ofHykwkabA50g6dfV T+TP1u0OiVku/i5s30zAIpJh4DR8Ni6hIIAMuWNSYKvm89GmqMCSSEeeQRmLRDi44Rtx ACoCJ+Ull1JYxdo0nkkNU8shNXWq4Svqzi0dzvGMJ7BYWGWs1UfN1LCWLjPB/dr5evm4 j6PA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=oTwwCo0HfzAnEhBsPRwUHRSIopGz31NRb8hCyw43RM8=; b=hCtdah5KuPEbkdUmWu58IsuztIsoCETcLHvTlq7ft1VkZntblrB0mG4FEIFE7ih7AM vT/w1ozWoY+1u662YYS4oJvX82apMdc6TfmlhvqGM67QNMO64u1HEUcAsqYdJ0Rtxgze JqcM+L6hDch3rDeF0MNYCAG9txQNWlv+NoWsWida7dZo5hNKfDmhyxoaNAS0p356YI8F MqdlIQJmMqK+L0nKv6VvsUxrhu/Ze5yar3uOB7okqSV6jN0O07fboBeE0pZfFC35+75s 7Wka3oDG9pWsvyDwpbl0vvvFU/4myxZEXGkLilJJbQ3IN1tgtH1gflKTc+sVEoZO7S7o aFEw== X-Gm-Message-State: AJcUukc5EKkwL9Cs8lXdXK9kstB4qv3anNQe0al3HmBqv2LjgMHrLraZ ixWdz5XqLRwSuxOcRRKSFT6CYHA9 X-Google-Smtp-Source: ALg8bN5NfYwj+WW+gUywrTzycE5MYu6AFVHziEt6KECTS+f0lqcsOHakmDBQPlzgLiIGfRATVs7YgA== X-Received: by 2002:a17:902:2bc5:: with SMTP id l63mr35787493plb.107.1548947755458; Thu, 31 Jan 2019 07:15:55 -0800 (PST) Received: from ?IPv6:2620:15c:2c1:200:55c7:81e6:c7d8:94b? ([2620:15c:2c1:200:55c7:81e6:c7d8:94b]) by smtp.gmail.com with ESMTPSA id w128sm7893873pfw.79.2019.01.31.07.15.54 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 31 Jan 2019 07:15:54 -0800 (PST) Subject: Re: [PATCH] net: check negative value for signed refcnt To: Kirill Tkhai , alexandre.besnard@softathome.com, davem@davemloft.net, ecree@solarflare.com, jiri@mellanox.com, petrm@mellanox.com, alexander.h.duyck@intel.com, amritha.nambiar@intel.com, lirongqing@baidu.com Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <20190131132008.23161-1-alexandre.besnard@softathome.com> <8b654b17-f8b4-0c89-26b5-311aeb703f6d@virtuozzo.com> From: Eric Dumazet Message-ID: <7bc31b61-8852-88a7-12bf-494c0e54574b@gmail.com> Date: Thu, 31 Jan 2019 07:15:53 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <8b654b17-f8b4-0c89-26b5-311aeb703f6d@virtuozzo.com> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 01/31/2019 05:49 AM, Kirill Tkhai wrote: > > 2)Not related to your patch -- it looks like we have problem in existing > code with this netdev_refcnt_read(). It does not imply a memory ordering > or some guarantees about reading percpu values. For example, in generic > code struct percpu_ref switches a counter into atomic mode before it checks > for the last reference. But there is nothing in netdev_refcnt_read(). Well, if we read an old value here, after a full and expensive synchronize_net(), then we would have lot more problems than simply having a second round in netdev_wait_allrefs()