[PATCH net] net: fix spurious TX timeout after dev_activate()

[PATCH net] net: fix spurious TX timeout after dev_activate()

[Breno Leitao]

While debugging another issue today, I found out that my TX queue is
stopped for 136.07 years (4294907392 ms).

    bnxt_en 0002:01:00.0 eth0: NETDEV WATCHDOG: CPU: 28: transmit queue 23 timed out 4294907392 ms

4294907392 is not an elapsed time. It is the value of jiffies at that
moment: INITIAL_JIFFIES is 4294667296.

dev_activate() runs transition_one_qdisc() over every TX queue, which
resets trans_start to 0, and then stamps only queue 0 through
netif_trans_update().

Stamp jiffies instead. A queue stopped across dev_activate() now gets a
full watchdog_timeo of grace, and is still reported if it is stopped
that long.

Fixes: 9b36627acecd ("net: remove dev->trans_start")
Cc: stable@vger.kernel.org
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 net/sched/sch_generic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index ef2b4bf515641..4539dc2c6d380 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -1278,7 +1278,7 @@ static void transition_one_qdisc(struct net_device *dev,
 
 	rcu_assign_pointer(dev_queue->qdisc, new_qdisc);
 	if (need_watchdog_p) {
-		WRITE_ONCE(dev_queue->trans_start, 0);
+		WRITE_ONCE(dev_queue->trans_start, jiffies);
 		*need_watchdog_p = 1;
 	}
 }

---
base-commit: 0a0d1d55dad570724bf8c7ea83409639cfb4be9b
change-id: 20260824-trans_start-557ecd4c8866

Best regards,
--  
Breno Leitao <leitao@debian.org>

Re: [PATCH net] net: fix spurious TX timeout after dev_activate()

[Nicolai Buchwitz]

Hi Breno

On 24.8.2026 13:45, Breno Leitao wrote:
> While debugging another issue today, I found out that my TX queue is
> stopped for 136.07 years (4294907392 ms).

nit: 4294907392 ms is ~49.7 days

> 
>     bnxt_en 0002:01:00.0 eth0: NETDEV WATCHDOG: CPU: 28: transmit queue 
> 23 timed out 4294907392 ms
> 
> 4294907392 is not an elapsed time. It is the value of jiffies at that
> moment: INITIAL_JIFFIES is 4294667296.
> 
> dev_activate() runs transition_one_qdisc() over every TX queue, which
> resets trans_start to 0, and then stamps only queue 0 through
> netif_trans_update().
> 
> Stamp jiffies instead. A queue stopped across dev_activate() now gets a
> full watchdog_timeo of grace, and is still reported if it is stopped
> that long.
> 
> Fixes: 9b36627acecd ("net: remove dev->trans_start")
> Cc: stable@vger.kernel.org
> Signed-off-by: Breno Leitao <leitao@debian.org>
> ---
>  net/sched/sch_generic.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
> index ef2b4bf515641..4539dc2c6d380 100644
> --- a/net/sched/sch_generic.c
> +++ b/net/sched/sch_generic.c
> @@ -1278,7 +1278,7 @@ static void transition_one_qdisc(struct 
> net_device *dev,
> 
>  	rcu_assign_pointer(dev_queue->qdisc, new_qdisc);
>  	if (need_watchdog_p) {
> -		WRITE_ONCE(dev_queue->trans_start, 0);
> +		WRITE_ONCE(dev_queue->trans_start, jiffies);
>  		*need_watchdog_p = 1;
>  	}
>  }

Follow up or v2: netif_trans_update() in dev_activate() now seems 
redundant?

> 
> ---
> base-commit: 0a0d1d55dad570724bf8c7ea83409639cfb4be9b
> change-id: 20260824-trans_start-557ecd4c8866
> 
> Best regards,
> --
> Breno Leitao <leitao@debian.org>

Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>

Thanks,
Nicolai