linux-kernel - Re: [PATCH net-next 1/3] net: ti: prueth: Fix kernel warning while bringing down network interface

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Message-ID: <48519536-6756-4d3d-9bb1-09197248df36@ti.com>
Date: Fri, 21 Mar 2025 13:31:29 +0530
From: "Malladi, Meghana" <m-malladi@...com>
To: Simon Horman <horms@...nel.org>
CC: <pabeni@...hat.com>, <kuba@...nel.org>, <edumazet@...gle.com>,
        <davem@...emloft.net>, <andrew+netdev@...n.ch>, <bpf@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <kory.maincent@...tlin.com>,
        <javier.carrasco.cruz@...il.com>, <diogo.ivo@...mens.com>,
        <jacob.e.keller@...el.com>, <john.fastabend@...il.com>,
        <hawk@...nel.org>, <daniel@...earbox.net>, <ast@...nel.org>,
        <srk@...com>, Vignesh Raghavendra
	<vigneshr@...com>,
        Roger Quadros <rogerq@...nel.org>, <danishanwar@...com>
Subject: Re: [PATCH net-next 1/3] net: ti: prueth: Fix kernel warning while
 bringing down network interface

Hi Simon,
Thanks for reviewing the patch series.

On 3/20/2025 6:23 PM, Simon Horman wrote:
> On Mon, Mar 17, 2025 at 03:45:48PM +0530, Meghana Malladi wrote:
>> During network interface initialization, the NIC driver needs to register
>> its Rx queue with the XDP, to ensure the incoming XDP buffer carries a
>> pointer reference to this info and is stored inside xdp_rxq_info.
>>
>> While this struct isn't tied to XDP prog, if there are any changes in
>> Rx queue, the NIC driver needs to stop the Rx queue by unregistering
>> with XDP before purging and reallocating memory. Drop page_pool destroy
>> during Rx channel reset and this is already handled by XDP during
>> xdp_rxq_info_unreg (Rx queue unregister), failing to do will cause the
>> following warning:
>>
>> [  271.494611] ------------[ cut here ]------------
>> [  271.494629] WARNING: CPU: 0 PID: 2453 at /net/core/page_pool.c:1108 0xffff8000808d5f60
> 
> I think it would be nice to include a bit more of the stack trace here.
> 

Sure, I will attach a link to the warning logs in v2.

>>
>> Fixes: 46eeb90f03e0 ("net: ti: icssg-prueth: Use page_pool API for RX buffer allocation")
>> Signed-off-by: Meghana Malladi <m-malladi@...com>
> 
> It is a shame that we now have more asymmetry regarding
> the allocation of the pool and unwind on error prueth_prepare_rx_chan().
> 
> But if I see things correctly the freeing of the pool via
> xdp_rxq_info_unreg() is unconditional. And with that in mind
> I agree the approach taken by this patch makes sense.
> 

Agreed on the asymmetry part, but I am not quite convinced on why 
xdp_rxq_info_unreg() is freeing the pool unconditionally, when the 
driver is the one which is allocating the pool. If xdp_rxq_info_unreg() 
is freeing it, then shouldn't xdp_rxq_info_reg() be allocating it ?

> Reviewed-by: Simon Horman <horms@...nel.org>
> 
> ...