On Mon, 2014-08-18 at 15:07 +0200, Michal Kazior wrote: > 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). Ah ok. > 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. Well, it's safe, but it's more efficient to call the _many() because otherwise you require rcu_synchronize() for each one. I'll apply this, to -next for now, later we can decide if we want to send it to stable or so? johannes -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
