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Date: Tue, 21 Apr 2026 14:54:37 +0300
From: Petko Manolov <petkan@nucleusys.com>
To: Morduan Zang <zhangdandan@uniontech.com>
Cc: Andrew Lunn <andrew+netdev@lunn.ch>,
	"David S . Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	linux-usb@vger.kernel.org, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] net: usb: rtl8150: free skb on usb_submit_urb() failure
 in xmit
Message-ID: <20260421115437.GB15539@bender.k.g>
References: <678BC10BB9E39322+20260421111025.15833-1-zhangdandan@uniontech.com>
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In-Reply-To: <678BC10BB9E39322+20260421111025.15833-1-zhangdandan@uniontech.com>

On 26-04-21 19:10:25, Morduan Zang wrote:
> When rtl8150_start_xmit() fails to submit the tx URB, the URB is never
> handed to the USB core and write_bulk_callback() will not run.  The
> driver returns NETDEV_TX_OK, which tells the networking stack that the
> skb has been consumed, but nothing actually frees the skb on this
> error path:
> 
>   dev->tx_skb = skb;
>   ...
>   if ((res = usb_submit_urb(dev->tx_urb, GFP_ATOMIC))) {
>           ...
>           /* no kfree_skb here */
>   }
>   return NETDEV_TX_OK;
> 
> This leaks the skb on every submit failure and also leaves dev->tx_skb
> pointing at memory that the driver itself may later free, which is
> fragile.
> 
> Free the skb with dev_kfree_skb_any() in the error path and clear
> dev->tx_skb so no stale pointer is left behind.

Another approach would be to use skb_copy_from_linear_data() to a static buffer
and free the skb right away.  Take a look at pegasus_start_xmit() in
drivers/net/usb/pegasus.c.  This comes at the cost of yet another memcpy,
though.

The above is not to say i don't like your current approach, just FYI.


		Petko