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

["John W. Linville" <linville@xxxxxxxxxxxxx>]

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@xxxxxxxxxxxxxx>
> ---
> 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...?

-- 
John W. Linville		Someday the world will need a hero, and you
linville@xxxxxxxxxxxxx			might be all we have.  Be ready.
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