mac80211: Prevent AP probing during suspend

Submitting AP probe/null during suspend can cause unexpected
disconnect on resume because of timeout waiting for ack status:

wlan0: Failed to send nullfunc to AP 11:22:33:44:55:66 after 500ms, disconnecting

This is especially the case when we enter suspend when a scan is
ongoing, indeed, scan is cancelled from __ieee80211_suspend, leading
to a corresponding (aborted) scan complete event, which in turn causes
the submission of an immediate monitor null frame (restart_sta_timer).
The corresponding packet or ack will not be processed before resuming,
causing a timeout & disconnect on resume.

Delay the AP probing when suspending/suspended.

Signed-off-by: Loic Poulain <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Johannes Berg <[e-mail]>

net/mac80211/ieee80211_i.h

···
 	 */
 	bool suspended;
 
+	/* suspending is true during the whole suspend process */
+	bool suspending;
+
 	/*
 	 * Resuming is true while suspended, but when we're reprogramming the
 	 * hardware -- at that time it's allowed to use ieee80211_queue_work()

net/mac80211/mlme.c

···
 		goto out;
 	}
 
+	if (sdata->local->suspending) {
+		/* reschedule after resume */
+		mutex_unlock(&sdata->local->mtx);
+		ieee80211_reset_ap_probe(sdata);
+		goto out;
+	}
+
 	if (beacon) {
 		mlme_dbg_ratelimited(sdata,
 				     "detected beacon loss from AP (missed %d beacons) - probing\n",

net/mac80211/pm.c

···
 	if (!local->open_count)
 		goto suspend;
 
+	local->suspending = true;
+	mb(); /* make suspending visible before any cancellation */
+
 	ieee80211_scan_cancel(local);
 
 	ieee80211_dfs_cac_cancel(local);
···
 	/* need suspended to be visible before quiescing is false */
 	barrier();
 	local->quiescing = false;
+	local->suspending = false;
 
 	return 0;
 }