netdev - Re: [PATCH] net: qrtr: Update packets cloning when broadcasting

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Message-ID: <9e23310b-c165-446f-9e99-c1bf61fe3e83@quicinc.com>
Date: Thu, 19 Sep 2024 06:35:51 -0700
From: Chris Lew <quic_clew@...cinc.com>
To: Youssef Samir <quic_yabdulra@...cinc.com>, <mani@...nel.org>,
        <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <andersson@...nel.org>
CC: <quic_jhugo@...cinc.com>, <linux-arm-msm@...r.kernel.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Carl Vanderlip
	<quic_carlv@...cinc.com>
Subject: Re: [PATCH] net: qrtr: Update packets cloning when broadcasting



On 9/17/2024 10:25 AM, Youssef Samir wrote:
> Hi Chris,
> 
> On 9/17/2024 3:59 PM, Chris Lew wrote:
>> Hi Youssef,
>>
>> On 9/16/2024 10:08 AM, Youssef Samir wrote:
>>> When broadcasting data to multiple nodes via MHI, using skb_clone()
>>> causes all nodes to receive the same header data. This can result in
>>> packets being discarded by endpoints, leading to lost data.
>>>
>>> This issue occurs when a socket is closed, and a QRTR_TYPE_DEL_CLIENT
>>> packet is broadcasted. All nodes receive the same destination node ID,
>>> causing the node connected to the client to discard the packet and
>>> remain unaware of the client's deletion.
>>>
>>
>> I guess this never happens for the SMD/RPMSG transport because the skb is consumed within the context of qrtr_node_enqueue where as MHI queues the skb to be transmitted later.
>>
>> Does the duplicate destination node ID match the last node in the qrtr_all_nodes list?
> 
> Yes, it always matches the last node in the qrtr_all_nodes list.
> 

Thanks for the confirmation, we haven't seen this before since most of 
our platforms usually only use one MHI qrtr node.

Reviewed-by: Chris Lew <quic_clew@...cinc.com>

>>
>>
>>> Replace skb_clone() with pskb_copy(), to create a separate copy of
>>> the header for each sk_buff.
>>>
>>> Fixes: bdabad3e363d ("net: Add Qualcomm IPC router")
>>> Signed-off-by: Youssef Samir <quic_yabdulra@...cinc.com>
>>> Reviewed-by: Jeffery Hugo <quic_jhugo@...cinc.com>
>>> Reviewed-by: Carl Vanderlip <quic_carlv@...cinc.com>
>>> ---
>>>    net/qrtr/af_qrtr.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/net/qrtr/af_qrtr.c b/net/qrtr/af_qrtr.c
>>> index 41ece61eb57a..00c51cf693f3 100644
>>> --- a/net/qrtr/af_qrtr.c
>>> +++ b/net/qrtr/af_qrtr.c
>>> @@ -884,7 +884,7 @@ static int qrtr_bcast_enqueue(struct qrtr_node *node, struct sk_buff *skb,
>>>          mutex_lock(&qrtr_node_lock);
>>>        list_for_each_entry(node, &qrtr_all_nodes, item) {
>>> -        skbn = skb_clone(skb, GFP_KERNEL);
>>> +        skbn = pskb_copy(skb, GFP_KERNEL);
>>>            if (!skbn)
>>>                break;
>>>            skb_set_owner_w(skbn, skb->sk);
>