Re: [PATCH 1/1] usb: dwc3: gadget: fix IRQ storm on invalid event buffer count

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

On Mon, Jul 27, 2026, Jiazi Liu wrote:
> When dwc3_check_event_buf() reads a GEVNTCOUNT value exceeding the
> event buffer length, commit 63ccd26cd1f6 ("usb: dwc3: gadget: check
> that event count does not exceed event buffer length") returns IRQ_NONE
> without writing back GEVNTCOUNT. Since the DWC3 interrupt is
> level-triggered, the uncleared IRQ source keeps the line asserted,
> causing a tight IRQ storm that accumulates 99,900 unhandled interrupts
> and triggers spurious.c:184 BUG -> kernel panic.
> 
> The resulting call stack:
>   __report_bad_irq+0xac/0xc8
>   note_interrupt+0x340/0x468
>   handle_irq_event+0xac/0xc0
>   handle_fasteoi_irq+0x120/0x228
>   gic_handle_irq+0x68/0x108
>   ...
>   kernel BUG at kernel/irq/spurious.c:184
> 
> To reproduce, write a bogus value exceeding the event buffer length
> directly to the GEVNTCOUNT register:
> 
>   devmem <DWC3_BASE + 0xc40c> 4 0x1004
> 
> Write the bogus count back to GEVNTCOUNT to clear the IRQ source,
> consistent with the stale event clearing pattern in
> dwc3_event_buffers_setup(), and schedule a soft disconnect via
> softcon_work to recover the controller state.
> 
> Fixes: 63ccd26cd1f6 ("usb: dwc3: gadget: check that event count does not exceed event buffer length")
> Cc: stable@vger.kernel.org
> Signed-off-by: Jiazi Liu <liujiazi@amazon.com>
> ---
>  drivers/usb/dwc3/core.h   |  2 ++
>  drivers/usb/dwc3/gadget.c | 23 ++++++++++++++++++++++-
>  2 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
> index 608daeb7ef10..0881ed7e956e 100644
> --- a/drivers/usb/dwc3/core.h
> +++ b/drivers/usb/dwc3/core.h
> @@ -1004,6 +1004,7 @@ struct dwc3_glue_ops {
>  /**
>   * struct dwc3 - representation of our controller
>   * @drd_work: workqueue used for role swapping
> + * @softcon_work: workqueue used for soft connect/disconnect recovery

Rename this to err_recovery_work and update the description.

>   * @ep0_trb: trb which is used for the ctrl_req
>   * @bounce: address of bounce buffer
>   * @setup_buf: used while precessing STD USB requests
> @@ -1189,6 +1190,7 @@ struct dwc3_glue_ops {
>   */
>  struct dwc3 {
>  	struct work_struct	drd_work;
> +	struct work_struct	softcon_work;
>  	struct dwc3_trb		*ep0_trb;
>  	void			*bounce;
>  	u8			*setup_buf;
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index fa0f16ffafef..9b24259272a4 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -4669,7 +4669,18 @@ static irqreturn_t dwc3_check_event_buf(struct dwc3_event_buffer *evt)
>  	if (count > evt->length) {
>  		dev_err_ratelimited(dwc->dev, "invalid count(%u) > evt->length(%u)\n",
>  			count, evt->length);

We probably no longer need the dev_err to be ratelimited.

> -		return IRQ_NONE;
> +		/*
> +		 * The DWC3 interrupt is level-triggered. Returning IRQ_NONE

This comment is out of context now that it's no longer IRQ_NONE. Most of
the details here are only relevant if we return IRQ_NONE. What we need
to document here why this is a fatal error and require reinitializing
the controller. Document that the driver and the controller are out of
sync to which event is consumed.

> +		 * without clearing the IRQ source leaves the line asserted,
> +		 * causing a tight IRQ storm that triggers spurious.c:184 BUG.
> +		 * Write the bogus count back to GEVNTCOUNT to clear the source,
> +		 * consistent with the stale event clearing in
> +		 * dwc3_event_buffers_setup(), then schedule a soft disconnect
> +		 * to recover the controller state.
> +		 */
> +		dwc3_writel(dwc->regs, DWC3_GEVNTCOUNT(0), count);
> +		schedule_work(&dwc->softcon_work);
> +		return IRQ_HANDLED;
>  	}
>  
>  	evt->count = count;
> @@ -4729,6 +4740,14 @@ static void dwc_gadget_release(struct device *dev)
>  	kfree(gadget);
>  }
>  
> +static void dwc3_softcon_work(struct work_struct *work)
> +{
> +	struct dwc3 *dwc = container_of(work, struct dwc3, softcon_work);
> +
> +	dev_err(dwc->dev, "event buffer error: performing soft disconnect\n");

Remove this dev_err(). The error message should be at the caller where
the specific failure condition is known, not the generic work handler.

> +	dwc3_gadget_soft_disconnect(dwc);

Check and follow the dwc3_gadget_suspend() and dwc3_gadget_resume()
logic for soft-disconnect and soft-connect to make sure the internal
states are updated and notify the gadget drivers correctly.

Perhaps you can also recover with soft-connect after soft-disconnect.

> +}
> +
>  /**
>   * dwc3_gadget_init - initializes gadget related registers
>   * @dwc: pointer to our controller context structure
> @@ -4772,6 +4791,7 @@ int dwc3_gadget_init(struct dwc3 *dwc)
>  	}
>  
>  	init_completion(&dwc->ep0_in_setup);
> +	INIT_WORK(&dwc->softcon_work, dwc3_softcon_work);
>  	dwc->gadget = kzalloc_obj(struct usb_gadget);
>  	if (!dwc->gadget) {
>  		ret = -ENOMEM;
> @@ -4868,6 +4888,7 @@ void dwc3_gadget_exit(struct dwc3 *dwc)
>  	if (!dwc->gadget)
>  		return;
>  
> +	cancel_work_sync(&dwc->softcon_work);
>  	dwc3_enable_susphy(dwc, true);
>  	usb_del_gadget(dwc->gadget);
>  	dwc3_gadget_free_endpoints(dwc);
> -- 
> 2.50.1 (Apple Git-155)
> 

Thanks,
Thinh