Return-path: Received: from mail-wi0-f169.google.com ([209.85.212.169]:45792 "EHLO mail-wi0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751782AbaHRNHj convert rfc822-to-8bit (ORCPT ); Mon, 18 Aug 2014 09:07:39 -0400 Received: by mail-wi0-f169.google.com with SMTP id n3so3656786wiv.0 for ; Mon, 18 Aug 2014 06:07:38 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <1407769505.9844.8.camel@jlt4.sipsolutions.net> References: <1406553419-16196-1-git-send-email-michal.kazior@tieto.com> <1407769505.9844.8.camel@jlt4.sipsolutions.net> Date: Mon, 18 Aug 2014 15:07:38 +0200 Message-ID: (sfid-20140818_150744_469033_9A68A495) Subject: Re: [PATCH] mac80211: fix chantype recalc warning From: Michal Kazior To: Johannes Berg Cc: linux-wireless Content-Type: text/plain; charset=UTF-8 Sender: linux-wireless-owner@vger.kernel.org List-ID: On 11 August 2014 17:05, Johannes Berg wrote: > On Mon, 2014-07-28 at 15:16 +0200, Michal Kazior wrote: >> When a device driver is unloaded local->interfaces >> list is cleared. If there was more than 1 >> interface running and connected (bound to a >> chanctx) then chantype recalc was called and it >> ended up with compat being NULL causing a call >> trace warning. >> >> Warn if compat becomes NULL as a result of >> incompatible bss_conf.chandef of interfaces bound >> to a given channel context only. > > Err, this slipped my radar - where does this need to go? No big deal. The warning is just a small nuisance with multi-vif. You won't see this on a typical system. > > Also - is this really the right thing? Why does this happen in this > situation? Shouldn't they all be not connected or not have a chanctx or > be compatible? If you eject, e.g. plug a usb wifi device out, its driver will call ieee80211_unregister_hw() which calls ieee80211_remove_interfaces(). If there are still running interfaces that have a netdev (probably to avoid a deadlock on iflist_mtx?) each interface is *moved* to a temporary list for a later call to unregister_netdevice_many(). While unregister_netdevice_many() executes the local->interfaces is empty. ieee80211_recalc_chanctx_chantype() is called whenever a chanctx is unassigned from a vif as long as there are still references to that chanctx. If there is just 1 interface when device is ejected, then ieee80211_recalc_chanctx_chantype() is not called. If there is more than 1 running interfaces then the removal of each but the last one calls to ieee80211_recalc_chanctx_chantype(). Since local->interfaces is empty compat pointer stays NULL and this triggers WARN_ON_ONCE (but only the first one effectively dumps a trace). Another way to fix this would probably be to change ieee80211_remove_interfaces() to remove all interfaces one-by-one (instead of in bulk). It seems iflist_mtx can be temporarily released while iterating over interfaces for the sake of calling unregister_netdevice() for each one because RTNL is held all the time guaranteeing no new interfaces are added in the meantime. I'm not sure if it's perfectly safe to replace unregister_netdevice_many() just like that though. I can look more into it. Michał