In the function ieee80211_tx_dequeue() there is a locking sequence:
begin:
spin_lock(&local->queue_stop_reason_lock);
q_stopped = local->queue_stop_reasons[q];
spin_unlock(&local->queue_stop_reason_lock);
However small the chance (increased by ftracetest), an asynchronous
interrupt can occur in between of spin_lock() and spin_unlock(),
and the interrupt routine will attempt to lock the same
&local->queue_stop_reason_lock again.
This is the only remaining spin_lock() on local->queue_stop_reason_lock
that did not disable interrupts and could have possibly caused the deadlock
on the same CPU (core).
This will cause a costly reset of the CPU and wifi device or an
altogether hang in the single CPU and single core scenario.
This is the probable reproduce of the deadlock:
Apr 10 00:58:33 marvin-IdeaPad-3-15ITL6 kernel: Possible unsafe locking scenario:
Apr 10 00:58:33 marvin-IdeaPad-3-15ITL6 kernel: CPU0
Apr 10 00:58:33 marvin-IdeaPad-3-15ITL6 kernel: ----
Apr 10 00:58:33 marvin-IdeaPad-3-15ITL6 kernel: lock(&local->queue_stop_reason_lock);
Apr 10 00:58:33 marvin-IdeaPad-3-15ITL6 kernel: <Interrupt>
Apr 10 00:58:33 marvin-IdeaPad-3-15ITL6 kernel: lock(&local->queue_stop_reason_lock);
Apr 10 00:58:33 marvin-IdeaPad-3-15ITL6 kernel:
*** DEADLOCK ***
Fixes: 4444bc2116ae
Link: https://lore.kernel.org/all/1f58a0d1-d2b9-d851-73c3-93fcc607501c@xxxxxxxxxxxx/
Cc: Alexander Wetzel <alexander@xxxxxxxxxxxxxx>
Signed-off-by: Mirsad Goran Todorovac <mirsad.todorovac@xxxxxxxxxxxx>
---
net/mac80211/tx.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 7699fb410670..45cb8e7bcc61 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -3781,6 +3781,7 @@ struct sk_buff *ieee80211_tx_dequeue(struct ieee80211_hw *hw,
ieee80211_tx_result r;
struct ieee80211_vif *vif = txq->vif;
int q = vif->hw_queue[txq->ac];
+ unsigned long flags;
bool q_stopped;
WARN_ON_ONCE(softirq_count() == 0);
@@ -3789,9 +3790,9 @@ struct sk_buff *ieee80211_tx_dequeue(struct ieee80211_hw *hw,
return NULL;
begin:
- spin_lock(&local->queue_stop_reason_lock);
+ spin_lock_irqsave(&local->queue_stop_reason_lock, flags);
q_stopped = local->queue_stop_reasons[q];
- spin_unlock(&local->queue_stop_reason_lock);
+ spin_unlock_irqrestore(&local->queue_stop_reason_lock, flags);
if (unlikely(q_stopped)) {
/* mark for waking later */
--
2.30.2
