linux-kernel - Re: [PATCH net-next v2 1/6] net: ti: icssg-prueth: Add functions to create and destroy Rx/Tx queues

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Message-ID: <53cbd465-6925-4003-a13b-11fa1034819d@ti.com>
Date: Tue, 7 Oct 2025 00:24:53 +0530
From: "Malladi, Meghana" <m-malladi@...com>
To: Jakub Kicinski <kuba@...nel.org>
CC: <namcao@...utronix.de>, <jacob.e.keller@...el.com>,
        <christian.koenig@....com>, <sumit.semwal@...aro.org>,
        <sdf@...ichev.me>, <john.fastabend@...il.com>, <hawk@...nel.org>,
        <daniel@...earbox.net>, <ast@...nel.org>, <pabeni@...hat.com>,
        <edumazet@...gle.com>, <davem@...emloft.net>, <andrew+netdev@...n.ch>,
        <linaro-mm-sig@...ts.linaro.org>, <dri-devel@...ts.freedesktop.org>,
        <bpf@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <netdev@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <srk@...com>, Vignesh Raghavendra <vigneshr@...com>,
        Roger Quadros
	<rogerq@...nel.org>, <danishanwar@...com>
Subject: Re: [PATCH net-next v2 1/6] net: ti: icssg-prueth: Add functions to
 create and destroy Rx/Tx queues

Hi Jakub,

On 9/4/2025 6:18 AM, Jakub Kicinski wrote:
> On Mon, 1 Sep 2025 15:32:22 +0530 Meghana Malladi wrote:
>>   	if (!emac->xdpi.prog && !prog)
>>   		return 0;
>>   
>> -	WRITE_ONCE(emac->xdp_prog, prog);
>> +	if (netif_running(emac->ndev)) {
>> +		prueth_destroy_txq(emac);
>> +		prueth_destroy_rxq(emac);
>> +	}
>> +
>> +	old_prog = xchg(&emac->xdp_prog, prog);
>> +	if (old_prog)
>> +		bpf_prog_put(old_prog);
>> +
>> +	if (netif_running(emac->ndev)) {
>> +		ret = prueth_create_rxq(emac);
> 
> shutting the device down and freeing all rx memory for reconfig is not
> okay. If the system is low on memory the Rx buffer allocations may fail
> and system may drop off the network. You must either pre-allocate or
> avoid freeing the memory, and just restart the queues.

So I have been working on trying to address this comment and maintain 
parity with the existing support provided by this series but looks like 
I might be missing something which is causing some regressions.

I am facing an issue with zero copy Rx, where there is some active 
traffic being received by the DUT (running in copy mode - default state)
and I switch to zero copy mode using AF-XDP_example [1], I am not able 
to receive any packets because I observe that the napi_rx_poll is not 
getting scheduled for whatever reason, ending up draining the rx 
descriptors and leading to memory leak. But if I first switch from copy 
to zero copy mode and then try sending traffic I am able to receive 
traffic on long runs without any failure or crash. I am not able to 
figure out why is this happening, so sharing my changes [2] on top of 
this series, which I made to address your comment. I am wondering if you 
could have a look and give me some pointers here. Thank you.

[1] https://github.com/xdp-project/bpf-examples/tree/main/AF_XDP-example

[2] 
https://gist.github.com/MeghanaMalladiTI/4c1cb106aee5bef4489ab372938d62d9

> 
>> +		if (ret) {
>> +			netdev_err(emac->ndev, "Failed to create RX queue: %d\n", ret);
>> +			return ret;
>> +		}
>> +
>> +		ret = prueth_create_txq(emac);
>> +		if (ret) {
>> +			netdev_err(emac->ndev, "Failed to create TX queue: %d\n", ret);
>> +			prueth_destroy_rxq(emac);
>> +			emac->xdp_prog = NULL;
>> +			return ret;
>> +		}
>> +	}
>>   
>>   	xdp_attachment_setup(&emac->xdpi, bpf);

-- 
Thanks,
Meghana Malladi