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

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Message-ID: <34d674a3cef104b3b3417645f8b52f0c8972ac08.camel@microchip.com>
Date: Tue, 18 Mar 2025 02:51:44 +0000
From: <Thangaraj.S@...rochip.com>
To: <gerhard@...leder-embedded.com>
CC: <andrew+netdev@...n.ch>, <Bryan.Whitehead@...rochip.com>,
	<davem@...emloft.net>, <linux-kernel@...r.kernel.org>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <edumazet@...gle.com>, <UNGLinuxDriver@...rochip.com>,
	<netdev@...r.kernel.org>
Subject: Re: [PATCH net] net: ethernet: microchip: lan743x: Fix memory
 allocation failure

Hi Gerhard,
Thanks for reviewing the patch. Please find my response inline.

On Fri, 2025-03-14 at 21:37 +0100, Gerhard Engleder wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you
> know the content is safe
> 
> 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.
> 

Yes, you are right. GFP ATOMIC cannot be removed. Will address this in
the next revision of the patch

> Gerhard
>