netdev - Re: [net 05/27] can: dev: can_get_echo_skb(): prevent call to kfree

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Date:   Wed, 4 Nov 2020 18:46:44 +0100
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     Jakub Kicinski <kuba@...nel.org>,
        Marc Kleine-Budde <mkl@...gutronix.de>
Cc:     Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        Eric Dumazet <edumazet@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>, linux-can@...r.kernel.org,
        kernel@...gutronix.de
Subject: Re: [net 05/27] can: dev: can_get_echo_skb(): prevent call to
 kfree_skb() in hard IRQ context

On 04.11.20 17:02, Jakub Kicinski wrote:
> On Wed, 4 Nov 2020 15:59:25 +0100 Oliver Hartkopp wrote:
>> On 04.11.20 09:16, Eric Dumazet wrote:

>>> So skb_orphan(skb) in CAN before calling netif_rx() is better IMO.
>>>    
>>
>> Unfortunately you missed the answer from Vincent, why skb_orphan() does
>> not work here:
>>
>> https://lore.kernel.org/linux-can/CAMZ6RqJyZTcqZcq6jEzm5LLM_MMe=dYDbwvv=Y+dBR0drWuFmw@mail.gmail.com/
> 
> Okay, we can take this as a quick fix but to me it seems a little
> strange to be dropping what is effectively locally generated frames.

Thanks! So this patch doesn't hinder Marc's PR :-)

> Can we use a NAPI poll model here and back pressure TX if the echo
> is not keeping up?

Some of the CAN network drivers already support NAPI.

@Marc: Can we also use NAPI for echo'ing the skbs?

Best regards,
Oliver