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=-11.4 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL 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 93720C433E2 for ; Thu, 17 Sep 2020 06:52:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 461852083B for ; Thu, 17 Sep 2020 06:52:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="OXBVMolK" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726222AbgIQGwA (ORCPT ); Thu, 17 Sep 2020 02:52:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44194 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726106AbgIQGv6 (ORCPT ); Thu, 17 Sep 2020 02:51:58 -0400 Received: from mail-il1-x142.google.com (mail-il1-x142.google.com [IPv6:2607:f8b0:4864:20::142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A102AC06174A for ; Wed, 16 Sep 2020 23:51:57 -0700 (PDT) Received: by mail-il1-x142.google.com with SMTP id t18so1236031ilp.5 for ; Wed, 16 Sep 2020 23:51:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=WmO3lehPU5xgp/AaU9lW0DTy2BiuALKSxjt4YpqCbPQ=; b=OXBVMolKXu9oHOH/RIVylOl8xeQHwn7gTVs/vMb1xmk0j8xZdei1Po6uQNaOcCi0rz k/Jz5O9iQZos06Ktg9342AdyYAQwGZNtt26Mwkfv0C35hYQyYctENMR8d/OqQCdpTbS4 QBVmNA9+8VsrdPxfGbmfu219GQDfZJ9EL/j/jHq9WnPHJTfkYv+T4y1pLQUGrLNHA1yd Mu7KIvQVM+I6p+UhhZw2Ji0gC497GSvFD0it8TrSqlO5Fam7Zk3fnx1S3HpBdVjy6wU/ saKkt6Ejo4b5N/r+CYf70DfONvV0JcvnKQ7ZIyaC2Sr5OoAh9KEn6JuJd1g+gpIB7kCk SIsw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=WmO3lehPU5xgp/AaU9lW0DTy2BiuALKSxjt4YpqCbPQ=; b=W3T5LmhkXXfgSRw7sz+6H7qDEcXYqSaYoxL3dXpwWMMkGDsOe8FDw37J2+QVj66IFW U4bdsEAof3EUKIMkmPHTpBpNvhj3Ah5WFJHrXRjedq7YdrU6qqMFL6rvnaK/x6PiYrbz 5PGKXdGUMbE6Eo/WId47qs/vcz6s/ye3vlQgrpQdWHidFbvYgjHD1RXwsD9ls87XDrVe nVs0nhyjgdTLogTiZlAb/Dg24/59KQByHjVNnmf5WXtgkLlXhQAFLxglJusit1NRdTnQ GDPye/j+HBKtOSunAG8FqUJvdsmV/Zo+CRiXOVEMpKlmtZMQlzQUtxvxHPu3TXiKLzPQ iTcA== X-Gm-Message-State: AOAM532wD1ouBr3gU9kwSwTiwC+kmzzGaGrRh7zMTIP+MM34wpJUwbQr mZf6ikkz0lbEjAidfxTCvXBijkzKeHK/hd8SpNgCFg== X-Google-Smtp-Source: ABdhPJxFYzwV1YLidOSKXI1r/DxKCDAaTVJyjocue5dOmnluWfcXOUoJWW2TLVCA5K/Yy25eZFSB7+QxpoVqTOXas+8= X-Received: by 2002:a92:d48b:: with SMTP id p11mr19958635ilg.69.1600325516756; Wed, 16 Sep 2020 23:51:56 -0700 (PDT) MIME-Version: 1.0 References: <20200917020021.0860995C06B9@us180.sjc.aristanetworks.com> In-Reply-To: From: Eric Dumazet Date: Thu, 17 Sep 2020 08:51:45 +0200 Message-ID: Subject: Re: [PATCH] net: make netdev_wait_allrefs wake-able To: Francesco Ruggeri Cc: open list , netdev , Cong Wang , Taehee Yoo , Andrii Nakryiko , Jiri Pirko , Alexei Starovoitov , Jakub Kicinski , David Miller Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 17, 2020 at 8:33 AM Francesco Ruggeri wrote: > > > static inline void dev_put(struct net_device *dev) > > { > > + struct task_struct *destroy_task = dev->destroy_task; > > + > > this_cpu_dec(*dev->pcpu_refcnt); > > + if (destroy_task) > > + wake_up_process(destroy_task); > > } > > I just realized that this introduces a race, if dev_put drops the last > reference, an already running netdev_wait_allrefs runs to completion > and then dev_put tries to wake it up. > Any suggestions on how to avoid this without resorting to > locking? > Honestly I would not touch dev_put() at all. Simply change the msleep(250) to something better, with maybe exponential backoff.