linux-kernel - Re: [PATCH net] netdevsim: disable local BH when scheduling NAPI

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Message-ID: <CANn89iKnqeDCrEsa4=vf1XV4N6+FUbfB8S6tXG6n8V+LKGfBEg@mail.gmail.com>
Date: Wed, 12 Feb 2025 19:55:32 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Breno Leitao <leitao@...ian.org>
Cc: Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew+netdev@...n.ch>, 
	"David S. Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, David Wei <dw@...idwei.uk>, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, paulmck@...nel.org, 
	kernel-team@...a.com, stable@...r.kernel.org
Subject: Re: [PATCH net] netdevsim: disable local BH when scheduling NAPI

On Wed, Feb 12, 2025 at 7:34 PM Breno Leitao <leitao@...ian.org> wrote:
>
> The netdevsim driver was getting NOHZ tick-stop errors during packet
> transmission due to pending softirq work when calling napi_schedule().
>
> This is showing the following message when running netconsole selftest.
>
>         NOHZ tick-stop error: local softirq work is pending, handler #08!!!
>
> Add local_bh_disable()/enable() around the napi_schedule() call to
> prevent softirqs from being handled during this xmit.
>
> Cc: stable@...r.kernel.org
> Fixes: 3762ec05a9fb ("netdevsim: add NAPI support")
> Suggested-by: Jakub Kicinski <kuba@...nel.org>
> Signed-off-by: Breno Leitao <leitao@...ian.org>
> ---
>  drivers/net/netdevsim/netdev.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
> index 42f247cbdceecbadf27f7090c030aa5bd240c18a..6aeb081b06da226ab91c49f53d08f465570877ae 100644
> --- 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()

Could you give more details ?