netdev - Re: [PATCH net] idpf: Fix incorrect NULL check in completion descriptor release

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Message-ID: <8347f99e-8f00-43c0-b492-4b0b6653bbe5@intel.com>
Date: Mon, 17 Nov 2025 11:30:10 +0100
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Alok Tiwari <alok.a.tiwari@...cle.com>
CC: <alok.a.tiwarilinux@...il.com>, <michal.kubiak@...el.com>,
	<przemyslaw.kitszel@...el.com>, <anthony.l.nguyen@...el.com>,
	<andrew+netdev@...n.ch>, <kuba@...nel.org>, <davem@...emloft.net>,
	<edumazet@...gle.com>, <pabeni@...hat.com>, <horms@...nel.org>,
	<intel-wired-lan@...ts.osuosl.org>, <netdev@...r.kernel.org>
Subject: Re: [PATCH net] idpf: Fix incorrect NULL check in completion
 descriptor release

From: Alok Tiwari <alok.a.tiwari@...cle.com>
Date: Mon, 17 Nov 2025 02:22:25 -0800

> idpf_compl_queue uses a union for comp, comp_4b, and desc_ring.
> The release path should check complq->desc_ring to determine whether the
> DMA descriptor ring was allocated. The existing check against
> complq->comp is incorrect, as only desc_ring reliably reflects the
> allocation status.

How can it be "incorrect" if these 3 are in the same union and have the
same size of 1 pointer? Any of them reflects the allocation status.

While your change improves readability, it doesn't fixes anything at
all. You can compare the object code to see there's no difference
before/after.

C unions are not the same as C++ unions, but even if the kernel had
`-fstrict-aliasing` enabled (and it's always disabled), the result would
be same. And C unions definitely don't work like std::variant.

So this could only go to -next as a cosmetic change if you really want this.

> 
> Fixes: cfe5efec9177 ("idpf: add 4-byte completion descriptor definition")
> Signed-off-by: Alok Tiwari <alok.a.tiwari@...cle.com>
> ---
>  drivers/net/ethernet/intel/idpf/idpf_txrx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/intel/idpf/idpf_txrx.c b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> index 828f7c444d30..1e7ae6f969ac 100644
> --- a/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> +++ b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> @@ -134,7 +134,7 @@ static void idpf_compl_desc_rel(struct idpf_compl_queue *complq)
>  {
>  	idpf_xsk_clear_queue(complq, VIRTCHNL2_QUEUE_TYPE_TX_COMPLETION);
>  
> -	if (!complq->comp)
> +	if (!complq->desc_ring)
>  		return;
>  
>  	dma_free_coherent(complq->netdev->dev.parent, complq->size,

Thanks,
Olek