From mboxrd@z Thu Jan 1 00:00:00 1970 From: Calvin Owens Subject: Re: [PATCH] mac80211: Use RCU protection in ieee80211_get_tx_rates() Date: Thu, 13 Jun 2013 10:27:35 -0500 Message-ID: <20130613152735.GA1822@gmail.com> 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> <51B843C9.9090500@openwrt.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Cc: Johannes Berg , "Luis R. Rodriguez" , "John W. Linville" , linux-wireless@vger.kernel.org, linux-kernel@vger.kernel.org, ath9k-devel@lists.ath9k.org, netdev@vger.kernel.org, jcalvinowens@gmail.com To: Felix Fietkau Return-path: Content-Disposition: inline In-Reply-To: <51B843C9.9090500@openwrt.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wednesday 06/12 at 11:47 +0200, Felix Fietkau wrote: > 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(); > } > > /***********/ > Yep, that stops the RCU warning for me. Tested-by: Calvin Owens