Return-path: Received: from smtprelay0137.hostedemail.com ([216.40.44.137]:49483 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751259Ab3K3UjF (ORCPT ); Sat, 30 Nov 2013 15:39:05 -0500 Message-ID: <1385843940.2664.4.camel@joe-AO722> (sfid-20131130_213949_172029_4049992A) Subject: Re: [PATCH] net: mac80211: tx.c: be sure of 'sdata->vif.type' must be NL80211_IFTYPE_AP when be in NL80211_IFTYPE_AP case From: Joe Perches To: Johannes Berg Cc: Chen Gang , "John W. Linville" , rkuo , "linux-kernel@vger.kernel.org" , David Miller , linux-wireless@vger.kernel.org, netdev Date: Sat, 30 Nov 2013 12:39:00 -0800 In-Reply-To: <1385842134.6108.4.camel@jlt4.sipsolutions.net> References: <528AEFB7.4060301@gmail.com> <20131125011938.GB18921@codeaurora.org> <5292B845.3010404@gmail.com> <5292B8A0.7020409@gmail.com> <5294255E.7040105@gmail.com> <52957ADA.2080704@gmail.com> (sfid-20131127_055211_558798_A7DF5684) <1385739487.8656.1.camel@jlt4.sipsolutions.net> <5299D306.7070701@gmail.com> (sfid-20131130_125901_519610_EDA4068E) <1385816013.4327.1.camel@jlt4.sipsolutions.net> <5299ED38.4090509@gmail.com> <5299EFDD.6060405@gmail.com> (sfid-20131130_150205_984535_068F14A9) <1385842134.6108.4.camel@jlt4.sipsolutions.net> Content-Type: text/plain; charset="ISO-8859-1" Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: On Sat, 2013-11-30 at 21:08 +0100, Johannes Berg wrote: > On Sat, 2013-11-30 at 22:02 +0800, Chen Gang wrote: > > > >>> case NL80211_IFTYPE_AP: > > >>> - if (sdata->vif.type == NL80211_IFTYPE_AP) > > >>> - chanctx_conf = rcu_dereference(sdata->vif.chanctx_conf); > > >>> + chanctx_conf = rcu_dereference(sdata->vif.chanctx_conf); > > >>> if (!chanctx_conf) > > >>> goto fail_rcu; > > >>> +try_next: > > >> > > >> I don't think that's better than the (fairly obvious) fall-through, and > > >> has a pretty odd goto. Also, depending on the compiler, it still knows > > >> the previous case label and doesn't warn. > > >> > > > > > > Yeah, fall-through is obvious. But check 'A' again just near by "case A" > > > seems a little strange, and some of compilers (or some of versions) are > > > really not quit smart enough to know it is not a warning. > > > > > > > Sorry, the paragraph above may lead misunderstanding, I repeated again: > > > > - fall-through is obvious (although I did not notice it, originally). > > > > - Check 'A' again just near by "case A" seems a little strange. > > > > - Some compilers aren't quit smart enough to know 'chanctx_conf' is OK. > > I know. If you have any good ideas of how to make it more obvious to the > compiler, I'm all ears, I just don't like any of the solutions offered > so far (and you aren't the first to do so either) :-) > > FWIW, I find the label to be odd because if you're familiar with the > code then AP/AP_VLAN *should* be identical except for two special things > that are now linearly & neatly handled in the code (the first being the > 4-addr station, the second the chanctx assignment which always has to be > done regardless of 4-addr). IMHO the == check after case should be > enough to make a human reader take a closer look. I understand that you > didn't and that's OK since you were just trying to squelch compile > warnings, but I don't see that this one warrants much attention. The label/test could be moved to save a couple of lines of duplicated code. Maybe: net/mac80211/tx.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c index 70b5a05..b2160f4 100644 --- a/net/mac80211/tx.c +++ b/net/mac80211/tx.c @@ -1777,18 +1777,16 @@ netdev_tx_t ieee80211_subif_start_xmit(struct sk_buff *skb, } ap_sdata = container_of(sdata->bss, struct ieee80211_sub_if_data, u.ap); - chanctx_conf = rcu_dereference(ap_sdata->vif.chanctx_conf); - if (!chanctx_conf) - goto fail_rcu; - band = chanctx_conf->def.chan->band; - if (sta) - break; /* fall through */ case NL80211_IFTYPE_AP: - if (sdata->vif.type == NL80211_IFTYPE_AP) - chanctx_conf = rcu_dereference(sdata->vif.chanctx_conf); + chanctx_conf = rcu_dereference(ap_sdata->vif.chanctx_conf); if (!chanctx_conf) goto fail_rcu; + if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN) { + band = chanctx_conf->def.chan->band; + if (sta) + break; + } fc |= cpu_to_le16(IEEE80211_FCTL_FROMDS); /* DA BSSID SA */ memcpy(hdr.addr1, skb->data, ETH_ALEN);