Re: IBSS can't beacon after rejoin / regression in TSF syncing code?
From: Sujith Manoharan <hidden>
Date: 2014-01-27 04:30:51
Subsystem:
mac80211, the rest · Maintainers:
Johannes Berg, Linus Torvalds
Simon Wunderlich wrote:
we have found a regression in the IBSS creation/joining part of mac80211 which is appearently connected to the TSF-syncing patches introduced last year[1]. It prevents beaconing of an adhoc member after rejoining a cell when this cell is currently empty. The problem is present in at least 3.10 and 3.13. To reproduce, use two adhoc peers and let them join/leave in the following order: station 1: join station 2: join station 2: leave station 1: leave station 1: join now we would expect that station 1 sends beacons, but it doesn't. After inspecting the code, station 1 actually selected the "old" ibss network and waits for a beacon to sync the tsf which is never received, as all members already left the network. An easy workaround is to set the IBSS creator always to true.
The race condition is that station-1 (the creator) removes station-2 only after a while, based on the expiration/inactive timer. The small window that IEEE80211_IBSS_MERGE_INTERVAL introduces when ieee80211_ibss_disconnect() is called causes the race, since we assume that station-2 is still active and do not remove the BSS from cfg80211. I am not sure why we have to keep the BSS around when we are leaving the network. Is this patch the right approach ?
diff --git a/net/mac80211/ibss.c b/net/mac80211/ibss.c
index 771080e..e1688cd 100644
--- a/net/mac80211/ibss.c
+++ b/net/mac80211/ibss.c@@ -688,17 +688,18 @@ static int ieee80211_sta_active_ibss(struct ieee80211_sub_if_data *sdata) return active; } -static void ieee80211_ibss_disconnect(struct ieee80211_sub_if_data *sdata) +static void ieee80211_ibss_disconnect(struct ieee80211_sub_if_data *sdata, bool leave) { struct ieee80211_if_ibss *ifibss = &sdata->u.ibss; struct ieee80211_local *local = sdata->local; struct cfg80211_bss *cbss; struct beacon_data *presp; struct sta_info *sta; - int active_ibss; + int active_ibss = 0; u16 capability; - active_ibss = ieee80211_sta_active_ibss(sdata); + if (!leave) + active_ibss = ieee80211_sta_active_ibss(sdata); if (!active_ibss && !is_zero_ether_addr(ifibss->bssid)) { capability = WLAN_CAPABILITY_IBSS;
@@ -765,7 +766,7 @@ static void ieee80211_csa_connection_drop_work(struct work_struct *work) sdata_lock(sdata); - ieee80211_ibss_disconnect(sdata); + ieee80211_ibss_disconnect(sdata, false); synchronize_rcu(); skb_queue_purge(&sdata->skb_queue);
@@ -1721,7 +1722,7 @@ int ieee80211_ibss_leave(struct ieee80211_sub_if_data *sdata) { struct ieee80211_if_ibss *ifibss = &sdata->u.ibss; - ieee80211_ibss_disconnect(sdata); + ieee80211_ibss_disconnect(sdata, true); ifibss->ssid_len = 0; memset(ifibss->bssid, 0, ETH_ALEN);
Sujith