Return-path: Received: from mail-wi0-f169.google.com ([209.85.212.169]:47941 "EHLO mail-wi0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751564AbaHTRcU (ORCPT ); Wed, 20 Aug 2014 13:32:20 -0400 Date: Wed, 20 Aug 2014 20:32:11 +0300 From: Andreea Bernat To: Christian Lamparter Cc: linville@tuxdriver.com, linux-wireless@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, paulmck@linux.vnet.ibm.com Subject: Re: [PATCH] carl9170: Replace rcu_dereference() with rcu_access_pointer() Message-ID: <20140820173210.GA18892@ada> (sfid-20140820_193240_556204_BC2F4BA5) References: <20140817104806.GA14533@ada> <3029076.uaUkTd8nru@debian64> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <3029076.uaUkTd8nru@debian64> Sender: linux-wireless-owner@vger.kernel.org List-ID: On Mon, Aug 18, 2014 at 09:29:36PM +0200, Christian Lamparter wrote: > On Sunday, August 17, 2014 01:48:07 PM Andreea-Cristina Bernat wrote: > > The rcu_dereference() call is used directly in a condition. > > Since its return value is never dereferenced it is recommended to use > > "rcu_access_pointer()" instead of "rcu_dereference()". > > Therefore, this patch makes the replacement. > > [...] > > Signed-off-by: Andreea-Cristina Bernat > > --- > > drivers/net/wireless/ath/carl9170/main.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/net/wireless/ath/carl9170/main.c b/drivers/net/wireless/ath/carl9170/main.c > > index f8ded84..12018ff 100644 > > --- a/drivers/net/wireless/ath/carl9170/main.c > > +++ b/drivers/net/wireless/ath/carl9170/main.c > > @@ -1431,7 +1431,7 @@ static int carl9170_op_ampdu_action(struct ieee80211_hw *hw, > > return -EOPNOTSUPP; > > > > rcu_read_lock(); > > - if (rcu_dereference(sta_info->agg[tid])) { > > + if (rcu_access_pointer(sta_info->agg[tid])) { > > rcu_read_unlock(); > > return -EBUSY; > > } > > There's more. The check does not do a whole lot. I think *it* [the check] and the > rcu_read_[un]lock [and the return -EBUSY] can be removed completely from the > IEEE80211_AMPDU_TX_START code-path in carl9170_op_ampdu_action. > > It would be awesome, if you could you make a patch which removes this > unneeded cosmic-ray-protection check :-) . Could you tell me why you think that those lines have to be removed? I would like to fully understand this before I remove them. Thank you, Andreea > > Thanks > Christian