Return-path: Received: from eu1sys200aog107.obsmtp.com ([207.126.144.123]:54872 "EHLO eu1sys200aog107.obsmtp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751339Ab2EOGEr convert rfc822-to-8bit (ORCPT ); Tue, 15 May 2012 02:04:47 -0400 From: Soumik DAS To: "John Linville (linville@tuxdriver.com)" Cc: "linux-wireless (linux-wireless@vger.kernel.org)" , "Johannes Berg (johannes@sipsolutions.net)" , "Kalle Valo (kvalo@adurom.com)" Date: Tue, 15 May 2012 08:04:32 +0200 Subject: [PATCH] mac80211: Remove race condition in sending null frame to check AP status Message-ID: <2E48302EED53D048A7BA72B0A307FB511FB906BC9A@EXDCVYMBSTM005.EQ1STM.local> (sfid-20120515_080451_370994_6627F936) Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: mac80211 tries to verify the existence of the current AP by probing or sending a NULL frame in function ieee80211_mgd_probe_ap_send. It 1st sends a null frame to the AP, increments probe_send_count and waits for the ACK to the NULL frame for a finite duration of time. At times, it happens that by the time mac80211 gets to increment probe_send_count, the ACK for the NULL frame transmitted has already been processed. This leads to a race condition where mac80211 times out waiting for the ACK for the NULL frame causing unnecessary disconnection with the AP. Signed-off-by: Soumik Das --- net/mac80211/mlme.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c index dbd4bd9..a1213e4 100644 --- a/net/mac80211/mlme.c +++ b/net/mac80211/mlme.c @@ -1522,6 +1522,7 @@ static void ieee80211_mgd_probe_ap_send(struct ieee80211_sub_if_data *sdata) * anymore. The timeout will be reset if the frame is ACKed by * the AP. */ + ifmgd->probe_send_count++; if (sdata->local->hw.flags & IEEE80211_HW_REPORTS_TX_ACK_STATUS) { ifmgd->nullfunc_failed = false; ieee80211_send_nullfunc(sdata->local, sdata, 0); @@ -1538,7 +1539,6 @@ static void ieee80211_mgd_probe_ap_send(struct ieee80211_sub_if_data *sdata) 0, (u32) -1, true, false); } - ifmgd->probe_send_count++; ifmgd->probe_timeout = jiffies + msecs_to_jiffies(probe_wait_ms); run_again(ifmgd, ifmgd->probe_timeout); if (sdata->local->hw.flags & IEEE80211_HW_REPORTS_TX_ACK_STATUS) -- 1.7.5.4