netdev - Re: [PATCH net-next v5 3/9] net: devmem: Implement TX path

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Message-ID: <a003b144-0abf-4274-abff-a6e391a3e20b@kernel.org>
Date: Tue, 25 Feb 2025 11:03:27 -0700
From: David Ahern <dsahern@...nel.org>
To: Mina Almasry <almasrymina@...gle.com>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, virtualization@...ts.linux.dev,
 kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
 Donald Hunter <donald.hunter@...il.com>, Jakub Kicinski <kuba@...nel.org>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Simon Horman <horms@...nel.org>, Jonathan Corbet <corbet@....net>,
 Andrew Lunn <andrew+netdev@...n.ch>, Jeroen de Borst <jeroendb@...gle.com>,
 Harshitha Ramamurthy <hramamurthy@...gle.com>,
 Kuniyuki Iwashima <kuniyu@...zon.com>, Willem de Bruijn
 <willemb@...gle.com>, Neal Cardwell <ncardwell@...gle.com>,
 Stefan Hajnoczi <stefanha@...hat.com>,
 Stefano Garzarella <sgarzare@...hat.com>, "Michael S. Tsirkin"
 <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>, Shuah Khan <shuah@...nel.org>, sdf@...ichev.me,
 asml.silence@...il.com, dw@...idwei.uk, Jamal Hadi Salim <jhs@...atatu.com>,
 Victor Nogueira <victor@...atatu.com>, Pedro Tammela
 <pctammela@...atatu.com>, Samiullah Khawaja <skhawaja@...gle.com>,
 Kaiyuan Zhang <kaiyuanz@...gle.com>
Subject: Re: [PATCH net-next v5 3/9] net: devmem: Implement TX path

On 2/25/25 10:41 AM, Mina Almasry wrote:
> On Tue, Feb 25, 2025 at 5:04 AM Paolo Abeni <pabeni@...hat.com> wrote:
>>
>> On 2/22/25 8:15 PM, Mina Almasry wrote:
>> [...]
>>> @@ -119,6 +122,13 @@ void net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding)
>>>       unsigned long xa_idx;
>>>       unsigned int rxq_idx;
>>>
>>> +     xa_erase(&net_devmem_dmabuf_bindings, binding->id);
>>> +
>>> +     /* Ensure no tx net_devmem_lookup_dmabuf() are in flight after the
>>> +      * erase.
>>> +      */
>>> +     synchronize_net();
>>
>> Is the above statement always true? can the dmabuf being stuck in some
>> qdisc? or even some local socket due to redirect?
>>
> 
> Yes, we could have have netmems in the TX path in the qdisc or waiting
> for retransmits that still have references to the dmabuf, and that's
> fine here I think.

skbs with references to netmem from a dmabuf can get stuck in retransmit
queues for a long time. The comment should at least acknowledge that.