mac80211: Support not iterating over not-sdata-in-driver ifaces

Allow drivers to request that interface-iterator does NOT iterate
over interfaces that are not sdata-in-driver.  This will allow
us to fix crashes in ath10k (and possibly other drivers).

To summarize Johannes' explanation:

Consider

add interface wlan0
add interface wlan1
iterate active interfaces -> wlan0 wlan1
add interface wlan2
iterate active interfaces -> wlan0 wlan1 wlan2

If you apply this scenario to a restart, which ought to be functionally
equivalent to the normal startup, just compressed in time, you're
basically saying that today you get

add interface wlan0
add interface wlan1
iterate active interfaces -> wlan0 wlan1 wlan2 << problem here
add interface wlan2
iterate active interfaces -> wlan0 wlan1 wlan2

which yeah, totally seems wrong.

But fixing that to be

add interface wlan0
add interface wlan1
iterate active interfaces ->
<nothing>
add interface wlan2
iterate active interfaces -> <nothing>
(or
maybe -> wlan0 wlan1 wlan2 if the reconfig already completed)

This is also at least somewhat wrong, but better to not iterate
over something that exists in the driver than iterate over something
that does not.  Originally the first issue was causing crashes in
testing with lots of station vdevs on an ath10k radio, combined
with firmware crashing.

I ran with a similar patch for years with no obvious bad results,
including significant testing with ath9k and ath10k.
Signed-off-by: Ben Greear <greearb@candelatech.com>
Link: https://lore.kernel.org/r/20200922191957.25257-1-greearb@candelatech.comSigned-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/mac80211.h

@@ -5407,11 +5407,15 @@ void ieee80211_sched_scan_stopped(struct ieee80211_hw *hw);
  * @IEEE80211_IFACE_ITER_RESUME_ALL: During resume, iterate over all
  *	interfaces, even if they haven't been re-added to the driver yet.
  * @IEEE80211_IFACE_ITER_ACTIVE: Iterate only active interfaces (netdev is up).
+ * @IEEE80211_IFACE_SKIP_SDATA_NOT_IN_DRIVER: Skip any interfaces where SDATA
+ *	is not in the driver.  This may fix crashes during firmware recovery
+ *	for instance.
  */
 enum ieee80211_interface_iteration_flags {
 	IEEE80211_IFACE_ITER_NORMAL	= 0,
 	IEEE80211_IFACE_ITER_RESUME_ALL	= BIT(0),
 	IEEE80211_IFACE_ITER_ACTIVE	= BIT(1),
+	IEEE80211_IFACE_SKIP_SDATA_NOT_IN_DRIVER	= BIT(2),
 };
 
 /**

net/mac80211/util.c

@@ -785,6 +785,9 @@ static void __iterate_interfaces(struct ieee80211_local *local,
 		if (!(iter_flags & IEEE80211_IFACE_ITER_RESUME_ALL) &&
 		    active_only && !(sdata->flags & IEEE80211_SDATA_IN_DRIVER))
 			continue;
+		if ((iter_flags & IEEE80211_IFACE_SKIP_SDATA_NOT_IN_DRIVER) &&
+		    !(sdata->flags & IEEE80211_SDATA_IN_DRIVER))
+			continue;
 		if (ieee80211_sdata_running(sdata) || !active_only)
 			iterator(data, sdata->vif.addr,
 				 &sdata->vif);