On Wed, Feb 23, 2011 at 2:17 PM, Johannes Berg
<johannes@xxxxxxxxxxxxxxxx> wrote:
> On Wed, 2011-02-23 at 13:04 +0530, Vivek Natarajan wrote:
>> There is a race on sending a data frame before the tx completion
>> of nullfunc frame for enabling power save. As the data quickly
>> follows the nullfunc frame, the AP thinks that the station is out
>> of power save and continues to send the frames. Whereas in the
>> station, the nullfunc ack will be processed after the tx completion
>> of data frame and mac80211 goes to powersave. Thus the power
>> save state mismatch between the station and the AP causes some
>> data loss and some applications fail because of that. This patch
>> fixes this issue.
>>
>> Signed-off-by: Vivek Natarajan <vnatarajan@xxxxxxxxxxx>
>> ---
>> net/mac80211/mlme.c | 14 +++++++++++++-
>> net/mac80211/status.c | 2 --
>> 2 files changed, 13 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
>> index 7b3f9df..abb0116 100644
>> --- a/net/mac80211/mlme.c
>> +++ b/net/mac80211/mlme.c
>> @@ -738,9 +738,19 @@ void ieee80211_dynamic_ps_enable_work(struct work_struct *work)
>> return;
>>
>> if ((local->hw.flags & IEEE80211_HW_PS_NULLFUNC_STACK) &&
>> - (!(ifmgd->flags & IEEE80211_STA_NULLFUNC_ACKED)))
>> + (!(ifmgd->flags & IEEE80211_STA_NULLFUNC_ACKED))) {
>> + netif_tx_stop_all_queues(sdata->dev);
>> + /*
>> + * Flush all the frames queued in the driver before
>> + * going to power save
>> + */
>> + drv_flush(local, false);
>> ieee80211_send_nullfunc(local, sdata, 1);
>>
>> + /* Flush once again to get the tx status of nullfunc frame */
>> + drv_flush(local, false);
>> + }
>> +
>> if (!((local->hw.flags & IEEE80211_HW_REPORTS_TX_ACK_STATUS) &&
>> (local->hw.flags & IEEE80211_HW_PS_NULLFUNC_STACK)) ||
>> (ifmgd->flags & IEEE80211_STA_NULLFUNC_ACKED)) {
>> @@ -748,6 +758,8 @@ void ieee80211_dynamic_ps_enable_work(struct work_struct *work)
>> local->hw.conf.flags |= IEEE80211_CONF_PS;
>> ieee80211_hw_config(local, IEEE80211_CONF_CHANGE_PS);
>> }
>> +
>> + netif_tx_start_all_queues(sdata->dev);
>> }
>>
>> void ieee80211_dynamic_ps_timer(unsigned long data)
>> diff --git a/net/mac80211/status.c b/net/mac80211/status.c
>> index 010a559..8651851 100644
>> --- a/net/mac80211/status.c
>> +++ b/net/mac80211/status.c
>> @@ -318,8 +318,6 @@ void ieee80211_tx_status(struct ieee80211_hw *hw, struct sk_buff *skb)
>> if (info->flags & IEEE80211_TX_STAT_ACK) {
>> local->ps_sdata->u.mgd.flags |=
>> IEEE80211_STA_NULLFUNC_ACKED;
>> - ieee80211_queue_work(&local->hw,
>> - &local->dynamic_ps_enable_work);
>
> Is the patch still correct if you don't remove this? I realise it won't
> usually be necessary, but I think we don't flush the TX status tasklet
> on flush right now so in theory there could be a race there that this
> code would clean up after, right?
If this is not removed, dynamic_ps_enable work would be queued once
again. And if a new frame is transmitted before this work is executed,
mac80211 tries to go to PS immediately in this work instead of
actually waiting for the dynamic_ps_timeout.
Vivek.
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