wifi: mac80211: don't start TX with fq->lock to fix deadlock

ieee80211_txq_purge() calls fq_tin_reset() and
ieee80211_purge_tx_queue(); Both are then calling
ieee80211_free_txskb(). Which can decide to TX the skb again.

There are at least two ways to get a deadlock:

1) When we have a TDLS teardown packet queued in either tin or frags
   ieee80211_tdls_td_tx_handle() will call ieee80211_subif_start_xmit()
   while we still hold fq->lock. ieee80211_txq_enqueue() will thus
   deadlock.

2) A variant of the above happens if aggregation is up and running:
   In that case ieee80211_iface_work() will deadlock with the original
   task: The original tasks already holds fq->lock and tries to get
   sta->lock after kicking off ieee80211_iface_work(). But the worker
   can get sta->lock prior to the original task and will then spin for
   fq->lock.

Avoid these deadlocks by not sending out any skbs when called via
ieee80211_free_txskb().

Signed-off-by: Alexander Wetzel <alexander@wetzel-home.de>
Link: https://lore.kernel.org/r/20220915124120.301918-1-alexander@wetzel-home.de
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/net/mac80211/status.c b/net/mac80211/status.c
index 8e77fd2e9fdffc59364e3d4b706313560845aeb9..3f9ddd7f04b6461459f1ebf875aea7a1f809b278 100644 (file)
--- a/net/mac80211/status.c
+++ b/net/mac80211/status.c
@@ -729,7 +729,7 @@ static void ieee80211_report_used_skb(struct ieee80211_local *local,
 
                if (!sdata) {
                        skb->dev = NULL;
-               } else {
+               } else if (!dropped) {
                        unsigned int hdr_size =
                                ieee80211_hdrlen(hdr->frame_control);