From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755394Ab3FLJsL (ORCPT ); Wed, 12 Jun 2013 05:48:11 -0400 Received: from nbd.name ([46.4.11.11]:49779 "EHLO nbd.name" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751379Ab3FLJsJ (ORCPT ); Wed, 12 Jun 2013 05:48:09 -0400 Message-ID: <51B843C9.9090500@openwrt.org> Date: Wed, 12 Jun 2013 11:47:53 +0200 From: Felix Fietkau User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:17.0) Gecko/20130509 Thunderbird/17.0.6 MIME-Version: 1.0 To: Calvin Owens CC: Johannes Berg , "Luis R. Rodriguez" , "John W. Linville" , linux-wireless@vger.kernel.org, linux-kernel@vger.kernel.org, ath9k-devel@venema.h4ckr.net, netdev@vger.kernel.org Subject: Re: [PATCH] mac80211: Use RCU protection in ieee80211_get_tx_rates() References: <20130609225120.GA2789@gmail.com> <20130610042959.GA1902@gmail.com> <1370950926.8356.14.camel@jlt4.sipsolutions.net> <20130611171304.GA2189@gmail.com> <1370980523.8356.70.camel@jlt4.sipsolutions.net> <20130612075634.GA1649@gmail.com> <20130612080042.GA1695@gmail.com> In-Reply-To: <20130612080042.GA1695@gmail.com> X-Enigmail-Version: 1.5.1 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2013-06-12 10:00 AM, Calvin Owens wrote: > Copying the rate table should be done in an RCU read-side critical > section. I think this approach is wrong. The sta entry is also under RCU protection (no locking for read access in that part of the code. In a normal driver tx path, no extra rcu_read_lock/rcu_read_unlock is needed. Only if the driver does some scheduling outside of the tx function (which ath9k does), this RCU warning appears. How about this change instead: --- --- a/drivers/net/wireless/ath/ath9k/xmit.c +++ b/drivers/net/wireless/ath/ath9k/xmit.c @@ -1570,6 +1570,8 @@ void ath_txq_schedule(struct ath_softc * txq->axq_ampdu_depth >= ATH_AGGR_MIN_QDEPTH) return; + rcu_read_lock(); + ac = list_first_entry(&txq->axq_acq, struct ath_atx_ac, list); last_ac = list_entry(txq->axq_acq.prev, struct ath_atx_ac, list); @@ -1608,8 +1610,10 @@ void ath_txq_schedule(struct ath_softc * if (ac == last_ac || txq->axq_ampdu_depth >= ATH_AGGR_MIN_QDEPTH) - return; + break; } + + rcu_read_unlock(); } /***********/