mac80211: fix station wakeup powersave race

Consider the following (relatively unlikely) scenario:
 1) station goes to sleep while frames are buffered in driver
 2) driver blocks wakeup (until no more frames are buffered)
 3) station wakes up again
 4) driver unblocks wakeup

In this case, the current mac80211 code will do the following:
 1) WLAN_STA_PS_STA set
 2) WLAN_STA_PS_DRIVER set
 3) - nothing -
 4) WLAN_STA_PS_DRIVER cleared

As a result, no frames will be delivered to the client, even
though it is awake, until it sends another frame to us that
triggers ieee80211_sta_ps_deliver_wakeup() in sta_ps_end().

Since we now take the PS spinlock, we can fix this while at
the same time removing the complexity with the pending skb
queue function. This was broken since my commit 50a9432daeec
("mac80211: fix powersaving clients races") due to removing
the clearing of WLAN_STA_PS_STA in the RX path.

While at it, fix a cleanup path issue when a station is
removed while the driver is still blocking its wakeup.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index c24ca0d..3e57f96 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -1128,6 +1128,13 @@ static void sta_ps_end(struct sta_info *sta)
 	       sta->sta.addr, sta->sta.aid);
 
 	if (test_sta_flag(sta, WLAN_STA_PS_DRIVER)) {
+		/*
+		 * Clear the flag only if the other one is still set
+		 * so that the TX path won't start TX'ing new frames
+		 * directly ... In the case that the driver flag isn't
+		 * set ieee80211_sta_ps_deliver_wakeup() will clear it.
+		 */
+		clear_sta_flag(sta, WLAN_STA_PS_STA);
 		ps_dbg(sta->sdata, "STA %pM aid %d driver-ps-blocked\n",
 		       sta->sta.addr, sta->sta.aid);
 		return;