On Mon, 2013-02-11 at 13:24 -0800, Thomas Pedersen wrote:
> >> + sdata = container_of(ifmsh, struct ieee80211_sub_if_data, u.mesh);
> >> + rcu_read_lock();
> >
> > This is weird since you already did it outside the function?
>
> Yes, but we shouldn't rely on the caller creating an RCU read section?
I don't really see a problem with that, but the other locking issue
means that you need this anyway.
> >> +static int
> >> +ieee80211_mesh_rebuild_beacon(struct ieee80211_if_mesh *ifmsh)
> >> +{
> >> + struct ieee80211_sub_if_data *sdata;
> >> + struct beacon_data *old_bcn;
> >> + int ret;
> >> + sdata = container_of(ifmsh, struct ieee80211_sub_if_data, u.mesh);
> >> +
> >> + rcu_read_lock();
> >> + old_bcn = rcu_dereference(ifmsh->beacon);
> >> + ret = ieee80211_mesh_build_beacon(ifmsh);
> >
> > This looks totally wrong. You must protect the assignment to
> > ifmsg->beacon by some lock, so then you don't need the rcu_read_lock()
> > here since you're under that lock, so this should be
> > rcu_dereference_protected(..., lockdep_is_held(whatever_lock));
>
> OK, I guess we better protect assignment by some lock then :)
I'm sure there's some lock already? Otherwise doing mesh operations from
userspace and the workqueue would probably be quite racy?
> >> + if (sdata->vif.bss_conf.enable_beacon &&
> >> + (changed & (BSS_CHANGED_BEACON |
> >> + BSS_CHANGED_HT |
> >> + BSS_CHANGED_BASIC_RATES |
> >> + BSS_CHANGED_BEACON_INT)))
> >> + if (ieee80211_mesh_rebuild_beacon(&sdata->u.mesh))
> >> + return;
> >
> > Does that return make any sense?
>
> The alternative is to keep notifying the driver. I just wanted to stop
> everything since we're out of memory, but we can keep calling
> bss_info_change_notify() is you think that makes more sense.
Either way is fine to me.
> >> @@ -694,6 +833,7 @@ void ieee80211_stop_mesh(struct ieee80211_sub_if_data *sdata)
> >> sdata->vif.bss_conf.enable_beacon = false;
> >> clear_bit(SDATA_STATE_OFFCHANNEL_BEACON_STOPPED, &sdata->state);
> >> ieee80211_bss_info_change_notify(sdata, BSS_CHANGED_BEACON_ENABLED);
> >> + kfree_rcu(ifmsh->beacon, rcu_head);
> >
> > I think you should set it to NULL first, just so it's clearer.
>
> For who? It seems there is no need in this path, but OK.
You don't have any synchronize_rcu() here so how can you be sure there's
not someone, say in a tasklet, using ifmsh->beacon at this point?
> >> @@ -883,6 +1023,7 @@ void ieee80211_mesh_init_sdata(struct ieee80211_sub_if_data *sdata)
> >> skb_queue_head_init(&ifmsh->ps.bc_buf);
> >> spin_lock_init(&ifmsh->mesh_preq_queue_lock);
> >> spin_lock_init(&ifmsh->sync_offset_lock);
> >> + RCU_INIT_POINTER(ifmsh->beacon, NULL);
> >
> > Isn't everything initialized to 0/null?
>
> Yep, I wanted any needed RCU magic to happen here though.
I don't think there's any RCU magic, particularly not with
RCU_INIT_POINTER, but I don't mind the assignment much :)
johannes
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