On Mon, Feb 11, 2013 at 1:17 PM, Johannes Berg
<johannes@xxxxxxxxxxxxxxxx> wrote:
> On Mon, 2013-02-11 at 13:07 -0800, Thomas Pedersen wrote:
>
>> +static int
>> +ieee80211_mesh_build_beacon(struct ieee80211_if_mesh *ifmsh)
>> +{
>> + struct beacon_data *bcn;
>> + int head_len, tail_len;
>> + struct sk_buff *skb;
>> + struct ieee80211_mgmt *mgmt;
>> + struct ieee80211_chanctx_conf *chanctx_conf;
>> + enum ieee80211_band band;
>> + u8 *pos;
>> + struct ieee80211_sub_if_data *sdata;
>> + int hdr_len = offsetof(struct ieee80211_mgmt, u.beacon) +
>> + sizeof(mgmt->u.beacon);
>> +
>> + 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?
>> + chanctx_conf = rcu_dereference(sdata->vif.chanctx_conf);
>> + band = chanctx_conf->def.chan->band;
>
> could be NULL? I guess not at this point though.
Yeah it will have been set.
>> +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 :)
>> + 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.
>> changed |= ieee80211_mps_local_status_update(sdata);
>>
>> + if (WARN_ON(ieee80211_mesh_build_beacon(ifmsh))) {
>
> no warning for memory allocation failures please
OK.
>> @@ -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.
>> @@ -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.
--
Thomas
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