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

[Jiazi Liu <jiazi.liu1984@gmail.com>]

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
  * @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);
-		return IRQ_NONE;
+		/*
+		 * The DWC3 interrupt is level-triggered. Returning IRQ_NONE
+		 * 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");
+	dwc3_gadget_soft_disconnect(dwc);
+}
+
 /**
  * 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)