Hello Eric, On Wed, Feb 12, 2025 at 07:55:32PM +0100, Eric Dumazet wrote: > On Wed, Feb 12, 2025 at 7:34 PM Breno Leitao <leitao@xxxxxxxxxx> wrote: > > > > --- a/drivers/net/netdevsim/netdev.c > > +++ b/drivers/net/netdevsim/netdev.c > > @@ -87,7 +87,9 @@ static netdev_tx_t nsim_start_xmit(struct sk_buff *skb, struct net_device *dev) > > if (unlikely(nsim_forward_skb(peer_dev, skb, rq) == NET_RX_DROP)) > > goto out_drop_cnt; > > > > + local_bh_disable(); > > napi_schedule(&rq->napi); > > + local_bh_enable(); > > > > I thought all ndo_start_xmit() were done under local_bh_disable() I think it depends on the path? > Could you give more details ? There are several paths to ndo_start_xmit(), and please correct me if I am reading the code wrongly here. Common path: __dev_direct_xmit() local_bh_disable(); netdev_start_xmit() __netdev_start_xmit() ops->ndo_start_xmit(skb, dev); But, in some other cases, I see: netpoll_start_xmit() netdev_start_xmit() .... My reading is that not all cases have local_bh_disable() disabled before calling ndo_start_xmit(). Question: Must BH be disabled before calling ndo_start_xmit()? If so, the problem might be in the netpoll code!? Also, is it worth adding a DEBUG_NET_WARN_ON_ONCE()? Note: Jakub gave another suggestion on how to fix this, so, I send a v2 with a different approach: https://lore.kernel.org/all/20250213071426.01490615@xxxxxxxxxx/ Thanks for the review! --breno
