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=-1.1 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=ham 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 17448C169C4 for ; Wed, 6 Feb 2019 23:55:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D32E62084D for ; Wed, 6 Feb 2019 23:55:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="K2C8uELW" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726436AbfBFXzN (ORCPT ); Wed, 6 Feb 2019 18:55:13 -0500 Received: from mail-pg1-f178.google.com ([209.85.215.178]:40882 "EHLO mail-pg1-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726161AbfBFXzM (ORCPT ); Wed, 6 Feb 2019 18:55:12 -0500 Received: by mail-pg1-f178.google.com with SMTP id z10so3665494pgp.7 for ; Wed, 06 Feb 2019 15:55:12 -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=s1j/gBgJvl/VIdSo8MIpqK6KGQnSVKZ2+C4bK0DD0Xw=; b=K2C8uELWmxNr/KjGir2LLiFOjE+FDKuFO5bKIUFjRV7gH89bfBIFJAt7/E1cplX5HF K3azOhXJ5RzJozVdRwe3QdhzWHgA0rXvKAXYyG+K5/L8eBdIMFH6e2fWQ7AoLeFcZOc8 tq/zYhiYdsnGYx6w+8NEhPwyV/C6OaLv/RwwwB4Hkx0QFJ0pHpAOu74Zi2hvOC+8fcV5 hmDqnKvNsyATjZVIR9yt8H5WhX3nCDO8ympRBNnxPxQqSDD1bhvx9/JOXYeZbZpqHZXL xHGtyqPPAaA2yoP1xGf8NWEWTIF1ln31nPpxy6pY0bR2mjMgKDnpDoDLs24g4esXhfK5 wJZw== 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=s1j/gBgJvl/VIdSo8MIpqK6KGQnSVKZ2+C4bK0DD0Xw=; b=cTqLS95Q0GOcBrIZGKjq3Gja0fLQf7UjBVPjAxy9vkpUr21kHFZdDMxu+x8GQR0J29 XsqFAfKekMvwkyXkW50Spn38rH9g4dKnlTfdOkwqGir+8dgCFREYOqE+/Kn+kc45BUs6 gYEXodYcnLk1obfrDVLOH1bsmkK0wwzjg9QYsNhHdc0LrFS49DSm7rqdAxB5hrDlH4Im yFskPaMqf8Se9W2EUxJawgRn2AfLbyylE2gmQvAbdaeWOi+Hd20Wq/V+H5K1ou7pfP2y JRaYTcQl9k0pl0W8afo56H41wIWCABuEG5EtzTnOkS9Lhvd83PZ0xX7ajVTpFyNW4c8e cgkA== X-Gm-Message-State: AHQUAub/TmFOPInE8PYuMDqwAkaDUhpy4At1py8SUBTER8GyI8j2YTs3 gsZcXVaIB8g9JbzhFu73ZoPsReIe X-Google-Smtp-Source: AHgI3IbiuZZc8M0M4zdv+hX+3Fe9mENyXQtBY1sOX6Tkd4YwDguge6STkoSo1V2+f+aH8BEAPQcs6Q== X-Received: by 2002:a65:6110:: with SMTP id z16mr12206444pgu.330.1549497312127; Wed, 06 Feb 2019 15:55:12 -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 d11sm8867242pgi.25.2019.02.06.15.55.10 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 06 Feb 2019 15:55:10 -0800 (PST) Subject: Re: [Patch net-next v2] mlx5: use RCU lock in mlx5_eq_cq_get() To: Eric Dumazet , Cong Wang , netdev@vger.kernel.org Cc: Saeed Mahameed , Tariq Toukan References: <20190206230019.1303-1-xiyou.wangcong@gmail.com> <52ed9806-310d-bfeb-9610-0daefc1e66fa@gmail.com> From: Eric Dumazet Message-ID: Date: Wed, 6 Feb 2019 15:55:10 -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: <52ed9806-310d-bfeb-9610-0daefc1e66fa@gmail.com> Content-Type: text/plain; charset=utf-8 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 02/06/2019 03:36 PM, Eric Dumazet wrote: > > I suspect that you need a variant that makes sure refcount is not zero. > > ( Typical RCU rules apply ) > > if (cq && !refcount_inc_not_zero(&cq->refcount)) > cq = NULL; > > > See commit 6fa19f5637a6c22bc0999596bcc83bdcac8a4fa6 rds: fix refcount bug in rds_sock_addref > for a similar issue I fixed recently. > By the way, we also could avoid two atomics on the cq->refcount , by using rcu_read_lock()/unlock() in the two callers .