linux-kernel - Re: [PATCH net-next v1] net: devmem: NULL check netdev_nl_get_dma

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Message-ID: <aLcTQEN-sAHxASMI@mini-arch>
Date: Tue, 2 Sep 2025 08:54:40 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Mina Almasry <almasrymina@...gle.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>
Subject: Re: [PATCH net-next v1] net: devmem: NULL check
 netdev_nl_get_dma_dev return value

On 08/29, Jakub Kicinski wrote:
> On Fri, 29 Aug 2025 21:59:38 +0000 Mina Almasry wrote:
> > netdev_nl_get_dma_dev can return NULL. This happens in the unlikely
> > scenario that netdev->dev.parent is NULL, or all the calls to the
> > ndo_queue_get_dma_dev return NULL from the driver.
> 
> I probably have Friday brain but I don't see what you mean..
> In net-next net_devmem_bind_dmabuf() gets a dma_dev and returns
> -EOPNOTSUPP PTR if its NULL.

+1, the description and the fix are confusing.

Unless I'm missing something, the intent seems to be to avoid hitting
a WARN_ON in dma_buf_attach (really dma_buf_dynamic_attach) when the dma_dev
is NULL. Mina, can we do this in the callers of netdev_queue_get_dma_dev?