Re: [PATCH net-next v17 03/13] ax88179_178a: Split driver into library and device specific code

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] net: deadlock in ax88179_change_mtu() due to recursive rtnl_lock()
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commit bbebfb7ee3c4e848c7cc7bf989fd290de2e0c6f1
Author: Birger Koblitz <mail@birger-koblitz.de>
Subject: ax88179_178a: Split driver into library and device specific code

This commit splits the ax88179_178a module code into a common library and
device-specific code. It also renames the module to ax88179 and adds an
alias to the old name.

> diff --git a/drivers/net/usb/ax88179_lib.c b/drivers/net/usb/ax88179_lib.c
> new file mode 100644
> index 0000000000000..522ea2447a111
> --- /dev/null
> +++ b/drivers/net/usb/ax88179_lib.c
[ ... ]
> +int ax88179_change_mtu(struct net_device *net, int new_mtu)
> +{
> +	struct usbnet *dev = netdev_priv(net);
> +	u16 tmp16;
> +
> +	WRITE_ONCE(net->mtu, new_mtu);
> +	dev->hard_mtu = net->mtu + net->hard_header_len;
> +
> +	rtnl_lock();
> +	if (net->mtu > 1500) {

[Severity: High]
Does acquiring the RTNL lock here lead to a deadlock?

The core network stack already holds the RTNL mutex when it invokes the
.ndo_change_mtu callback (which is registered as ax88179_change_mtu in
ax88179_netdev_ops).

Since the RTNL mutex is non-recursive, attempting to acquire it again from
the same thread here in ax88179_change_mtu() will cause an immediate hang
whenever an MTU change is attempted on the network device.

> +		ax88179_read_cmd(dev, AX_ACCESS_MAC, AX_MEDIUM_STATUS_MODE,
> +				 2, 2, &tmp16);
> +		tmp16 |= AX_MEDIUM_JUMBO_EN;
> +		ax88179_write_cmd(dev, AX_ACCESS_MAC, AX_MEDIUM_STATUS_MODE,
> +				  2, 2, &tmp16);
> +	} else {
> +		ax88179_read_cmd(dev, AX_ACCESS_MAC, AX_MEDIUM_STATUS_MODE,
> +				 2, 2, &tmp16);
> +		tmp16 &= ~AX_MEDIUM_JUMBO_EN;
> +		ax88179_write_cmd(dev, AX_ACCESS_MAC, AX_MEDIUM_STATUS_MODE,
> +				  2, 2, &tmp16);
> +	}
> +	rtnl_unlock();
> +
> +	/* max qlen depend on hard_mtu and rx_urb_size */
> +	usbnet_update_max_qlen(dev);
> +
> +	return 0;
> +}

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Sashiko AI review · https://sashiko.dev/#/patchset/20261006-ax88179a-v17-0-252814fe35ea@birger-koblitz.de?part=3