Re: [PATCH net-next v6 4/5] net: sched: add timeout count to NETDEV WATCHDOG message

[Jesper Dangaard Brouer <hawk@kernel.org>]

On 04/06/2026 10.30, Paolo Abeni wrote:
> On 5/27/26 3:54 PM, hawk@kernel.org wrote:
>> diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
>> index 237ee1cd0136..2aebab985c00 100644
>> --- a/net/sched/sch_generic.c
>> +++ b/net/sched/sch_generic.c
>> @@ -533,13 +533,12 @@ static void dev_watchdog(struct timer_list *t)
>>   		    netif_running(dev) &&
>>   		    netif_carrier_ok(dev)) {
>>   			unsigned int timedout_ms = 0;
>> +			struct netdev_queue *txq;
>>   			unsigned int i;
>>   			unsigned long trans_start;
>>   			unsigned long oldest_start = jiffies;
>>   
>>   			for (i = 0; i < dev->num_tx_queues; i++) {
>> -				struct netdev_queue *txq;
>> -
>>   				txq = netdev_get_tx_queue(dev, i);
>>   				if (!netif_xmit_stopped(txq))
>>   					continue;
>> @@ -561,9 +560,10 @@ static void dev_watchdog(struct timer_list *t)
>>   
>>   			if (unlikely(timedout_ms)) {
>>   				trace_net_dev_xmit_timeout(dev, i);
>> -				netdev_crit(dev, "NETDEV WATCHDOG: CPU: %d: transmit queue %u timed out %u ms\n",
>> +				netdev_crit(dev, "NETDEV WATCHDOG: CPU: %d: transmit queue %u timed out %u ms (n:%ld)\n",
>>   					    raw_smp_processor_id(),
>> -					    i, timedout_ms);
>> +					    i, timedout_ms,
>> +					    atomic_long_read(&txq->trans_timeout));
> 
> It looks like txq could be uninitialized here if num_tx_queues is 0. I'm
> unsure if some weird/buggy device driver could actually hit that case,
> but grep '->num_tx_queues = 0;' has more than 0 hits in the current tree
> and I would err on the safe side.

Addressed in [V7], by reading out trans_timeout value when it is
accessed/incremented anyhow.  Thus, avoiding the need to deref txq.

[V7] https://lore.kernel.org/all/20260612083530.1650245-5-hawk@kernel.org/

--Jesper