netdev - Re: [PATCH net 2/4] net: ti: icssg-prueth: Report BQL before sending XDP packets

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Message-ID: <64396b06-5ea7-4da9-b854-b3d42f2b9bde@ti.com>
Date: Fri, 2 May 2025 11:48:47 +0530
From: "Malladi, Meghana" <m-malladi@...com>
To: Jakub Kicinski <kuba@...nel.org>
CC: <dan.carpenter@...aro.org>, <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>,
        <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 2/4] net: ti: icssg-prueth: Report BQL before sending
 XDP packets

Hi Jakub,

On 5/1/2025 8:23 PM, Jakub Kicinski wrote:
> On Mon, 28 Apr 2025 17:34:57 +0530 Meghana Malladi wrote:
>> When sending out any kind of traffic, it is essential that the driver
>> keeps reporting BQL of the number of bytes that have been sent so that
>> BQL can track the amount of data in the queue and prevents it from
>> overflowing. If BQL is not reported, the driver may continue sending
>> packets even when the queue is full, leading to packet loss, congestion
>> and decreased network performance. Currently this is missing in
>> emac_xmit_xdp_frame() and this patch fixes it.
> 
> The ordering of patches in the series is a bit off.
> The order should be something like:
> 
>    net: ti: icssg-prueth: Set XDP feature flags for ndev
>    net: ti: icssg-prueth: Fix kernel panic during concurrent Tx queue ...
>    net: ti: icssg-prueth: Fix race condition for traffic from different ...
>    net: ti: icssg-prueth: Report BQL before sending XDP packets
> 
> This patch is not correct without the extra locking in place.

Actually the order of bug fixes which I posted, is the order in which I 
fixed the bugs, while running xdp-trafficgen:
1. ndo_xdp_xmit() wasn't getting called because of missing XDP feature 
flags check.
2. kernel crash: kernel BUG at lib/dynamic_queue_limits.c:99! and was 
fixed by reporting BQL for packet transmission.My bad, I forgot  to add 
this in the commit message.
3. kernel crash: kernel BUG at lib/genalloc.c:508! due to memory 
corruption in DMA descriptors and fixed it with spinlock
4. kernel crash: kernel BUG at lib/dynamic_queue_limits.c:99! due to 
race condition in netif_txq and fixed it with __netif_tx_lock()

But yeah I think the order you suggested makes more sense. Let me try 
that and post v2.

-- 
Thanks,
Meghana Malladi