6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Eric Dumazet <edumazet@xxxxxxxxxx>
[ Upstream commit 95ecba62e2fd201bcdcca636f5d774f1cd4f1458 ]
Some workloads hit the infamous dev_watchdog() message:
"NETDEV WATCHDOG: eth0 (xxxx): transmit queue XX timed out"
It seems possible to hit this even for perfectly normal
BQL enabled drivers:
1) Assume a TX queue was idle for more than dev->watchdog_timeo
(5 seconds unless changed by the driver)
2) Assume a big packet is sent, exceeding current BQL limit.
3) Driver ndo_start_xmit() puts the packet in TX ring,
and netdev_tx_sent_queue() is called.
4) QUEUE_STATE_STACK_XOFF could be set from netdev_tx_sent_queue()
before txq->trans_start has been written.
5) txq->trans_start is written later, from netdev_start_xmit()
if (rc == NETDEV_TX_OK)
txq_trans_update(txq)
dev_watchdog() running on another cpu could read the old
txq->trans_start, and then see QUEUE_STATE_STACK_XOFF, because 5)
did not happen yet.
To solve the issue, write txq->trans_start right before one XOFF bit
is set :
- _QUEUE_STATE_DRV_XOFF from netif_tx_stop_queue()
- __QUEUE_STATE_STACK_XOFF from netdev_tx_sent_queue()
>From dev_watchdog(), we have to read txq->state before txq->trans_start.
Add memory barriers to enforce correct ordering.
In the future, we could avoid writing over txq->trans_start for normal
operations, and rename this field to txq->xoff_start_time.
Fixes: bec251bc8b6a ("net: no longer stop all TX queues in dev_watchdog()")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reviewed-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Reviewed-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Link: https://patch.msgid.link/20241015194118.3951657-1-edumazet@xxxxxxxxxx
Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
include/linux/netdevice.h | 12 ++++++++++++
net/sched/sch_generic.c | 8 +++++++-
2 files changed, 19 insertions(+), 1 deletion(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 8f5ac20b4c03d..1576e7443eee5 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3363,6 +3363,12 @@ static inline void netif_tx_wake_all_queues(struct net_device *dev)
static __always_inline void netif_tx_stop_queue(struct netdev_queue *dev_queue)
{
+ /* Paired with READ_ONCE() from dev_watchdog() */
+ WRITE_ONCE(dev_queue->trans_start, jiffies);
+
+ /* This barrier is paired with smp_mb() from dev_watchdog() */
+ smp_mb__before_atomic();
+
/* Must be an atomic op see netif_txq_try_stop() */
set_bit(__QUEUE_STATE_DRV_XOFF, &dev_queue->state);
}
@@ -3479,6 +3485,12 @@ static inline void netdev_tx_sent_queue(struct netdev_queue *dev_queue,
if (likely(dql_avail(&dev_queue->dql) >= 0))
return;
+ /* Paired with READ_ONCE() from dev_watchdog() */
+ WRITE_ONCE(dev_queue->trans_start, jiffies);
+
+ /* This barrier is paired with smp_mb() from dev_watchdog() */
+ smp_mb__before_atomic();
+
set_bit(__QUEUE_STATE_STACK_XOFF, &dev_queue->state);
/*
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 7f0c8df7b63e0..b51af871a621c 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -511,9 +511,15 @@ static void dev_watchdog(struct timer_list *t)
struct netdev_queue *txq;
txq = netdev_get_tx_queue(dev, i);
- trans_start = READ_ONCE(txq->trans_start);
if (!netif_xmit_stopped(txq))
continue;
+
+ /* Paired with WRITE_ONCE() + smp_mb...() in
+ * netdev_tx_sent_queue() and netif_tx_stop_queue().
+ */
+ smp_mb();
+ trans_start = READ_ONCE(txq->trans_start);
+
if (time_after(jiffies, trans_start + dev->watchdog_timeo)) {
timedout_ms = jiffies_to_msecs(jiffies - trans_start);
atomic_long_inc(&txq->trans_timeout);
--
2.43.0
