Subject: Re: [PATCH net-next 1/5] net: dpaa: avoid on-stack arrays of NR_CPUS elements

From: Breno Leitao <[email-masked]>
Date: Thu, 11 Jul 2024 04:16:51 -0700

Hello Vladimir,

On Thu, Jul 11, 2024 at 02:00:21AM +0300, Vladimir Oltean wrote:
> The dpaa-eth driver is written for PowerPC and Arm SoCs which have 1-24
> CPUs. It depends on CONFIG_NR_CPUS having a reasonably small value in
> Kconfig. Otherwise, there are 2 functions which allocate on-stack arrays
> of NR_CPUS elements, and these can quickly explode in size, leading to
> warnings such as:
> 
>   drivers/net/ethernet/freescale/dpaa/dpaa_eth.c:3280:12: warning:
>   stack frame size (16664) exceeds limit (2048) in 'dpaa_eth_probe' [-Wframe-larger-than]
> 
> The problem is twofold:
> - Reducing the array size to the boot-time num_possible_cpus() (rather
>   than the compile-time NR_CPUS) creates a variable-length array,
>   which should be avoided in the Linux kernel.
> - Using NR_CPUS as an array size makes the driver blow up in stack
>   consumption with generic, as opposed to hand-crafted, .config files.
> 
> A simple solution is to use dynamic allocation for num_possible_cpus()
> elements (aka a small number determined at runtime).
> 
> Link: https://lore.kernel.org/all/[email-masked]/
> Signed-off-by: Vladimir Oltean <[email-masked]>
Reviewed-by: Breno Leitao <[email-masked]>

Thanks for working on it.

--breno