linux-kernel - Re: [PATCH RFC net-next 0/4] net: page_pool: a couple assorted optimizations

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Date:   Mon, 3 Jul 2023 11:57:34 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Larysa Zaremba <larysa.zaremba@...el.com>,
        Yunsheng Lin <linyunsheng@...wei.com>,
        Alexander Duyck <alexanderduyck@...com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        "Ilias Apalodimas" <ilias.apalodimas@...aro.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC net-next 0/4] net: page_pool: a couple assorted
 optimizations

On Mon, 3 Jul 2023 15:50:55 +0200 Alexander Lobakin wrote:
> > The reason I did not do that is that I wasn't sure if there is no
> > weird (netcons?) case where skb gets freed from an IRQ :(  
> 
> Shouldn't they use dev_kfree_skb_any() or _irq()? Usage of plain
> kfree_skb() is not allowed in the TH :s

I haven't looked at the code so I could be lying but I thought that 
the only thing that can't run in hard IRQ context is the destructor,
so if the caller knows there's no destructor they can free the skb.

I'd ask you the inverse question. If the main use case is skb xdp
(which eh, uh, okay..) then why not make it use napi_consume_skb()?
I don't think skb XDP can run in hard IRQ context, can it?

> Anyway, if the flag really makes no sense, I can replace it with
> in_softirq(), it's my hobby to break weird drivers :D