On Wed, 2011-02-23 at 15:03 +0530, Vivek Natarajan wrote:
> 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.
Ok, thanks for the clarification.
johannes
--
To unsubscribe from this list: send the line "unsubscribe linux-wireless" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
