From 512119b36f7945a650877cbc7e9b5f4cc4d92e4c Mon Sep 17 00:00:00 2001 From: Christian Lamparter Date: Mon, 31 Jan 2011 20:48:44 +0200 Subject: mac80211: fix race between next beacon dtim and ieee80211_get_buffered_bc On review of 'zd1211rw: implement beacon fetching and handling ieee80211_get_buffered_bc()', Christian Lamparter noted that [1]: Since zd_beacon_done also uploads the next beacon so long in advance, there could be an equally long race between the outdated state of the next beacon's DTIM broadcast traffic indicator (802.11-2007 7.3.2.6) which -in your case- was uploaded almost a beacon interval ago and the xmit of ieee80211_get_buffered_bc *now*. The dtim bc/mc bit might be not set, when a mc/bc arrived after the beacon was uploaded, but before the "beacon done event" from the hardware. So, dozing stations don't expect the broadcast traffic and of course, they might miss it completely. It's probably better to fix this in mac80211 (see the attached hack). [1] http://marc.info/?l=linux-wireless&m=129435041117256&w=2 CC: Christian Lamparter Signed-off-by: Jussi Kivilinna Signed-off-by: John W. Linville --- net/mac80211/tx.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'net/mac80211/tx.c') diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c index 8fbbc7a..bf67a22 100644 --- a/net/mac80211/tx.c +++ b/net/mac80211/tx.c @@ -2179,6 +2179,8 @@ static void ieee80211_beacon_add_tim(struct ieee80211_if_ap *bss, if (bss->dtim_count == 0 && !skb_queue_empty(&bss->ps_bc_buf)) aid0 = 1; + bss->dtim_bc_mc = aid0 == 1; + if (have_bits) { /* Find largest even number N1 so that bits numbered 1 through * (N1 x 8) - 1 in the bitmap are 0 and number N2 so that bits @@ -2549,7 +2551,7 @@ ieee80211_get_buffered_bc(struct ieee80211_hw *hw, if (sdata->vif.type != NL80211_IFTYPE_AP || !beacon || !beacon->head) goto out; - if (bss->dtim_count != 0) + if (bss->dtim_count != 0 || !bss->dtim_bc_mc) goto out; /* send buffered bc/mc only after DTIM beacon */ while (1) { -- cgit v1.1