linux-kernel - Re: [PATCH net] net: ethernet: microchip: lan743x: Fix memory allocation failure

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Message-ID: <806eed8e-0695-450f-a16b-66b602db01dd@engleder-embedded.com>
Date: Fri, 14 Mar 2025 21:37:03 +0100
From: Gerhard Engleder <gerhard@...leder-embedded.com>
To: Thangaraj Samynathan <thangaraj.s@...rochip.com>
Cc: bryan.whitehead@...rochip.com, UNGLinuxDriver@...rochip.com,
 andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
 kuba@...nel.org, pabeni@...hat.com, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org
Subject: Re: [PATCH net] net: ethernet: microchip: lan743x: Fix memory
 allocation failure

On 14.03.25 08:02, Thangaraj Samynathan wrote:
> The driver allocates ring elements using GFP_ATOMIC and GFP_DMA
> flags. The allocation is not done in atomic context and there is
> no dependency from LAN743x hardware on memory allocation should be
> in DMA_ZONE. Hence modifying the flags to use only GFP_KERNEL.
> 
> Signed-off-by: Thangaraj Samynathan <thangaraj.s@...rochip.com>
> ---
>   drivers/net/ethernet/microchip/lan743x_main.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/microchip/lan743x_main.c b/drivers/net/ethernet/microchip/lan743x_main.c
> index 23760b613d3e..c10b0131d5fb 100644
> --- a/drivers/net/ethernet/microchip/lan743x_main.c
> +++ b/drivers/net/ethernet/microchip/lan743x_main.c
> @@ -2495,8 +2495,7 @@ static int lan743x_rx_process_buffer(struct lan743x_rx *rx)
>   
>   	/* save existing skb, allocate new skb and map to dma */
>   	skb = buffer_info->skb;
> -	if (lan743x_rx_init_ring_element(rx, rx->last_head,
> -					 GFP_ATOMIC | GFP_DMA)) {
> +	if (lan743x_rx_init_ring_element(rx, rx->last_head, GFP_KERNEL)) {

I agree with removing GFP_DMA. If it would be needed, then everywhere
and not only here in NAPI context as it is intended for hardware
limitations.

I'm not sure if GFP_ATOMIC can be removed. Isn't NAPI an atomic context?
For example napi_alloc_skb() and page_pool_dev_alloc_pages() use
GFP_ATOMIC.

Gerhard