Re: [PATCH] mac80211: Remove race condition in sending null frame to check AP status

["Arend van Spriel" <arend@broadcom.com>]

On 05/15/2012 04:00 PM, John W. Linville wrote:
> On Tue, May 15, 2012 at 08:04:32AM +0200, Soumik DAS wrote:
>> 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 <soumik.das@stericsson.com>
>> ---
>> 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
>>
> 
> Looks like whitespace damage...?
> 

Apparently, 4 spaces are used instead of real tabs.

Gr. AvS