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Date: Tue, 25 Feb 2025 11:03:27 -0700
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Subject: Re: [PATCH net-next v5 3/9] net: devmem: Implement TX path
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To: Mina Almasry <almasrymina@google.com>, Paolo Abeni <pabeni@redhat.com>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
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References: <20250222191517.743530-1-almasrymina@google.com>
 <20250222191517.743530-4-almasrymina@google.com>
 <a814c41a-40f9-4632-a5bb-ad3da5911fb6@redhat.com>
 <CAHS8izNfNJLrMtdR0je3DsXDAvP2Hs8HfKf5Jq7_kQJsVUbrzg@mail.gmail.com>
From: David Ahern <dsahern@kernel.org>
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On 2/25/25 10:41 AM, Mina Almasry wrote:
> On Tue, Feb 25, 2025 at 5:04 AM Paolo Abeni <pabeni@redhat.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.