Re: usb: gadget: u_serial: fix stale req->dep warn on disconnect/reconnect

[Daehwan Jung]

On Mon, Jul 27, 2026 at 01:26:32PM +0900, Daehwan Jung wrote:
> When DWC3_EP_DELAY_STOP defers ENDXFER, giveback of -ESHUTDOWN requests
> arrives after gserial_disconnect(). These stale requests then accumulate
> in read_pool via gs_rx_push(). After gadget exit frees the old endpoint,
> req->dep becomes a dangling pointer. On the next gserial_connect(),
> gs_start_rx() queues these stale requests onto a new endpoint, triggering:
> 
>   WARNING: CPU: 0 at drivers/usb/dwc3/gadget.c:1990
>   request 00000000e6e350a5 belongs to ''
> 
>   Call trace:
>    dwc3_gadget_ep_queue+0x158/0x1e8
>    usb_ep_queue+0x60/0xe8
>    gs_start_rx+0xa4/0x128
>    gs_start_io+0x128/0x254
>    gserial_connect+0xb4/0x14c
>    acm_set_alt+0xa0/0x114
>    set_config+0x22c/0x384
>    composite_setup+0x37c/0xc7c
>    configfs_composite_setup+0x5c/0x88
>    dwc3_ep0_interrupt+0x6c8/0xbcc
>    dwc3_thread_interrupt+0xa0/0x1284
>    irq_thread_fn+0x48/0xa8
>    irq_thread+0x150/0x31c
>    kthread+0x150/0x27c
>    ret_from_fork+0x10/0x20
> 
> Fix by discarding -ESHUTDOWN requests immediately in gs_read_complete()
> while ep is still valid, preventing stale reqs from entering read_pool.
> 
> Fixes: 937ef73d5075 ("USB: serial gadget: rx path data loss fixes")
> Signed-off-by: Daehwan Jung <dh10.jung@xxxxxxxxxxx>
> ---
> Changes in v2:
> - Correct the name of author
> - Modify commit subject (panic -> warn)
> Link to v1: https://lore.kernel.org/all/20260721013509.2327242-1-dh10.jung@xxxxxxxxxxx/
> ---
>  drivers/usb/gadget/function/u_serial.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
> index cdd1dfc666c4..97ee1b9cb065 100644
> --- a/drivers/usb/gadget/function/u_serial.c
> +++ b/drivers/usb/gadget/function/u_serial.c
> @@ -459,10 +459,22 @@ static void gs_read_complete(struct usb_ep *ep, struct usb_request *req)
>  {
>  	struct gs_port	*port = ep->driver_data;
>  
> -	/* Queue all received data until the tty layer is ready for it. */
>  	spin_lock(&port->port_lock);
> -	list_add_tail(&req->list, &port->read_queue);
> -	schedule_delayed_work(&port->push, 0);
> +	if (req->status == -ESHUTDOWN) {
> +		/*
> +		 * Discard shutdown completions here while ep is still valid.
> +		 * Returning them to read_pool after gserial_disconnect() has
> +		 * reset the counters causes stale reqs (with req->dep pointing
> +		 * to the old ep) to be queued onto a new ep at reconnect time,
> +		 * triggering a req->dep != dep WARN.
> +		 */
> +		gs_free_req(ep, req);
> +		port->read_started--;
> +	} else {
> +		/* Queue all received data until the tty layer is ready for it. */
> +		list_add_tail(&req->list, &port->read_queue);
> +		schedule_delayed_work(&port->push, 0);
> +	}
>  	spin_unlock(&port->port_lock);
>  }
>  
> -- 
> 2.34.1
> 
> 

I'm sorry, missing version tag in the subject.
v3 has been sent. Please ignore this v2.

Best Regards,
Daehwan Jung