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=-2.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_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 2C650C35666 for ; Sat, 22 Feb 2020 13:39:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 03A6420702 for ; Sat, 22 Feb 2020 13:39:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="GXLKlRfc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727401AbgBVNjj (ORCPT ); Sat, 22 Feb 2020 08:39:39 -0500 Received: from mail-pf1-f194.google.com ([209.85.210.194]:33470 "EHLO mail-pf1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727046AbgBVNji (ORCPT ); Sat, 22 Feb 2020 08:39:38 -0500 Received: by mail-pf1-f194.google.com with SMTP id n7so2839381pfn.0; Sat, 22 Feb 2020 05:39:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:date:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=vpxT9jClDrKoKxPt0kmgtgiiuZoHxIxpAJPkebvXON0=; b=GXLKlRfcHhBTYgl1ilH4o6mibl1xTvcNCPXZFQNec8/NOTrpQtsfA1JP8KaNs3aYYg IKfHktkagA44VixY1m/yaksXVZI5mnnwvskjvQ1JJWZKSVnvNsI/JcinID87RR5f7yjq rHGb0hKXst4/I4k0njMJlneWTL1tuJdQbyMx/seEwj0Zf3U4AsBFvjnM2hGQyFL6APOV TtrndIYAHC20+ueeYgIK9XVKf6e1xpCSPWecjH8LXHahEI3yc98+initYn99IdzOFo27 yid+lJqWR0oJoKtaGJcH7Tp8DfuMUG4Vdg6vkiq9v8McSlvmfVPiknC3XDMcYiyKlgA6 ASdQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:date:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=vpxT9jClDrKoKxPt0kmgtgiiuZoHxIxpAJPkebvXON0=; b=mr+7nvDcu/+zJwSEOSpAms3QJdZJ4/bXNBfYJf5Ne5yrHhuKxFEF/U0zgz5/fv67uC 2uAv05UOdF7hyFPUc9p1Bs+jWCtKguincnNl8ZSsJfHfU1cQ+P5DBG96AqzKndc3da7i 9CC4EkRo7KzDGM8cUBMzsmdhLJp7YFmpzNWr+5SO76X3NGHnR+vxt0x5gqjX7zFg09r4 vFq7wbKjB4lJ7BpigwXOARjmp75wOS19vVYuceTxFNtXtiSqTKVhYbGuaspB+wAOugBe XQyUfXTIs7NhrqRTp0A9LclFU/SBmNUjfaCMJKc97xWEU+aCMhnkMXlLH8CLG9RNrtmu AGeg== X-Gm-Message-State: APjAAAUkLars2E33PNLm6aqvtFeiAaXMNdhJe2Qhm8OtPa1dRqpXlsHN FdtjVXS92p6ayZPgYhPT3Q== X-Google-Smtp-Source: APXvYqwEKQ41EVLj6CR4+LTHf/M95sWALC35qShHEDBl/TpwOUcje2MB0Kb3HNksVa1H25ZDOgRBJg== X-Received: by 2002:a62:f243:: with SMTP id y3mr43858640pfl.146.1582378776499; Sat, 22 Feb 2020 05:39:36 -0800 (PST) Received: from madhuparna-HP-Notebook ([42.109.145.199]) by smtp.gmail.com with ESMTPSA id b12sm6517235pfr.26.2020.02.22.05.39.31 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 22 Feb 2020 05:39:35 -0800 (PST) From: Madhuparna Bhowmik X-Google-Original-From: Madhuparna Bhowmik Date: Sat, 22 Feb 2020 19:09:28 +0530 To: Johannes Berg Cc: madhuparnabhowmik10@gmail.com, davem@davemloft.net, linux-wireless@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, joel@joelfernandes.org, frextrite@gmail.com, linux-kernel-mentees@lists.linuxfoundation.org, paulmck@kernel.org Subject: Re: [PATCH] net: mac80211: rx.c: Use built-in RCU list checking Message-ID: <20200222133928.GA10397@madhuparna-HP-Notebook> References: <20200222101831.8001-1-madhuparnabhowmik10@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-wireless-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org On Sat, Feb 22, 2020 at 01:53:25PM +0100, Johannes Berg wrote: > On Sat, 2020-02-22 at 15:48 +0530, madhuparnabhowmik10@gmail.com wrote: > > From: Madhuparna Bhowmik > > > > list_for_each_entry_rcu() has built-in RCU and lock checking. > > > > Pass cond argument to list_for_each_entry_rcu() to silence > > false lockdep warning when CONFIG_PROVE_RCU_LIST is enabled > > by default. > > Umm. What warning? > If list_for_each_entry_rcu() is called from non rcu protection i.e without holding rcu_read_lock, but under the protection of a different lock then we can pass that as the condition for lockdep checking because otherwise lockdep will complain if list_for_each_entry_rcu() is used without rcu protection. So, if we do not pass this argument (cond) it may lead to false lockdep warnings. > > +++ b/net/mac80211/rx.c > > @@ -3547,7 +3547,8 @@ static void ieee80211_rx_cooked_monitor(struct ieee80211_rx_data *rx, > > skb->pkt_type = PACKET_OTHERHOST; > > skb->protocol = htons(ETH_P_802_2); > > > > - list_for_each_entry_rcu(sdata, &local->interfaces, list) { > > + list_for_each_entry_rcu(sdata, &local->interfaces, list, > > + lockdep_is_held(&rx->local->rx_path_lock)) { > > if (!ieee80211_sdata_running(sdata)) > > continue; > > This is not related at all. I analysed the following traces: ieee80211_rx_handlers() -> ieee80211_rx_handlers_result() -> ieee80211_rx_cooked_monitor() here ieee80211_rx_handlers() is holding the rx->local->rx_path_lock and therefore I used this for the cond argument. If this is not right, can you help me in figuring out that which other lock is held? and __ieee80211_rx_handle_packet() -> ieee80211_prepare_and_rx_handle() -> ieee80211_invoke_rx_handlers() -> ieee80211_rx_handlers_result() -> ieee80211_rx_cooked_monitor() Here __ieee80211_rx_handle_packet() should be called under rcu_read_lock protection. So this trace seems okay and no need to pass any cond. I may have missed something, please correct me in that case. > > @@ -4114,7 +4115,8 @@ void __ieee80211_check_fast_rx_iface(struct ieee80211_sub_if_data *sdata) > > > > lockdep_assert_held(&local->sta_mtx); > > > > - list_for_each_entry_rcu(sta, &local->sta_list, list) { > > + list_for_each_entry_rcu(sta, &local->sta_list, list, > > + lockdep_is_held(&local->sta_mtx)) { > > And this isn't even a real RCU iteration, since we _must_ hold the mutex > here. > Yeah exactly, dropping _rcu (use list_for_each_entry()) would be a good option in this case. Let me know if that is alright and I will send a new patch with all the changes required. Thank you, Madhuparna > johannes >