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

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Message-ID: <00293616-d738-48eb-becc-981a6ad86493@quicinc.com>
Date: Tue, 17 Sep 2024 18:25:46 +0100
From: Youssef Samir <quic_yabdulra@...cinc.com>
To: Chris Lew <quic_clew@...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

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.

> 
> 
>> 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);