Re: [PATCH] mac80211: do not call driver wake_tx_queue op during reconfig

[Felix Fietkau <nbd@nbd.name>]

On 2019-03-01 17:06, Felix Fietkau wrote:
> On 2019-03-01 16:29, Ben Greear wrote:
>> On 3/1/19 5:48 AM, Felix Fietkau wrote:
>>> There are several scenarios in which mac80211 can call drv_wake_tx_queue
>>> after ieee80211_restart_hw has been called and has not yet completed.
>>> Driver private structs are considered uninitialized until mac80211 has
>>> uploaded the vifs, stations and keys again, so using private tx queue
>>> data during that time is not safe.
>>> 
>>> The driver can also not rely on drv_reconfig_complete to figure out when
>>> it is safe to accept drv_wake_tx_queue calls again, because it is only
>>> called after all tx queues are woken again.
>>> 
>>> To fix this, bail out early in drv_wake_tx_queue if local->in_reconfig
>>> is set.
>> 
>> This reminded me of a patch I posted back in 2016.  The discussion just sort of
>> ended on it, but curious if you have a new opinion on it after debugging the
>> issue in this patch:
>> 
>> https://patchwork.kernel.org/patch/9457709/
>> 
>> For what its worth, I've been using the patch above since I posted it, and
>> it seems to work well for ath9k and ath10k.
> I agree with what Johannes wrote about that patch. Fixing this could
> likely be as simple as clearing IEEE80211_SDATA_IN_DRIVER on all
> interfaces before bringing any of them back up. That way the normal
> interface add logic applies without nasty special cases.
> The reconfig code checks for ieee80211_sdata_running (which is
> unaffected), so I don't think we need to save the previous value of that
> flag.
How about this? (untested)
---
--- a/net/mac80211/util.c
+++ b/net/mac80211/util.c
@@ -1956,7 +1956,6 @@ static void ieee80211_flush_completed_scan(struct ieee80211_local *local,
 
 static void ieee80211_handle_reconfig_failure(struct ieee80211_local *local)
 {
-	struct ieee80211_sub_if_data *sdata;
 	struct ieee80211_chanctx *ctx;
 
 	/*
@@ -1980,9 +1979,6 @@ static void ieee80211_handle_reconfig_failure(struct ieee80211_local *local)
 	 */
 	ieee80211_sched_scan_end(local);
 
-	list_for_each_entry(sdata, &local->interfaces, list)
-		sdata->flags &= ~IEEE80211_SDATA_IN_DRIVER;
-
 	/* Mark channel contexts as not being in the driver any more to avoid
 	 * removing them from the driver during the shutdown process...
 	 */
@@ -2135,6 +2131,9 @@ int ieee80211_reconfig(struct ieee80211_local *local)
 
 	local->started = false;
 
+	list_for_each_entry(sdata, &local->interfaces, list)
+		sdata->flags &= ~IEEE80211_SDATA_IN_DRIVER;
+
 	/*
 	 * Upon resume hardware can sometimes be goofy due to
 	 * various platform / driver / bus issues, so restarting