[PATCH] usb: dwc3: fix race of usb_gadget_driver operation

[Linyu Yuan <linyyuan@xxxxxxxxxxxxxx>]

there is following race condition,

      CPU1                         CPU2
dwc3_runtime_suspend()        dwc3_gadget_stop()
spin_lock(&dwc->lock)
dwc3_gadget_suspend()
dwc3_disconnect_gadget()
dwc->gadget_driver != NULL
spin_unlock(&dwc->lock)
                              spin_lock(&dwc->lock)
                              dwc->gadget_driver = NULL
                              spin_unlock(&dwc->lock)
dwc->gadget_driver->disconnect(dwc->gadget);

system will crash when access NULL gadget_driver.

7dc0c55e9f30 ('USB: UDC core: Add udc_async_callbacks gadget op')
suggest a common way to avoid such kind of race.

this change implment the callback in dwc3 and
change related functions which have callback to UDC core.

Signed-off-by: Linyu Yuan <linyyuan@xxxxxxxxxxxxxx>
---
 drivers/usb/dwc3/core.h   |  1 +
 drivers/usb/dwc3/ep0.c    |  5 +++--
 drivers/usb/dwc3/gadget.c | 39 +++++++++++++++++++++++----------------
 3 files changed, 27 insertions(+), 18 deletions(-)

diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
index dccdf13b5f9e..5991766239ba 100644
--- a/drivers/usb/dwc3/core.h
+++ b/drivers/usb/dwc3/core.h
@@ -1279,6 +1279,7 @@ struct dwc3 {
 	unsigned		dis_metastability_quirk:1;
 
 	unsigned		dis_split_quirk:1;
+	unsigned		async_callbacks:1;
 
 	u16			imod_interval;
 };
diff --git a/drivers/usb/dwc3/ep0.c b/drivers/usb/dwc3/ep0.c
index 3cd294264372..26419077c7c9 100644
--- a/drivers/usb/dwc3/ep0.c
+++ b/drivers/usb/dwc3/ep0.c
@@ -597,10 +597,11 @@ static int dwc3_ep0_set_address(struct dwc3 *dwc, struct usb_ctrlrequest *ctrl)
 
 static int dwc3_ep0_delegate_req(struct dwc3 *dwc, struct usb_ctrlrequest *ctrl)
 {
-	int ret;
+	int ret = 0;
 
 	spin_unlock(&dwc->lock);
-	ret = dwc->gadget_driver->setup(dwc->gadget, ctrl);
+	if (dwc->async_callbacks)
+		ret = dwc->gadget_driver->setup(dwc->gadget, ctrl);
 	spin_lock(&dwc->lock);
 	return ret;
 }
diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index af6d7f157989..d868f30007cc 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -2585,6 +2585,16 @@ static int dwc3_gadget_vbus_draw(struct usb_gadget *g, unsigned int mA)
 	return ret;
 }
 
+static void dwc3_gadget_async_callbacks(struct usb_gadget *g, bool enable)
+{
+	struct dwc3		*dwc = gadget_to_dwc(g);
+	unsigned long		flags;
+
+	spin_lock_irqsave(&dwc->lock, flags);
+	dwc->async_callbacks = enable;
+	spin_unlock_irqrestore(&dwc->lock, flags);
+}
+
 static const struct usb_gadget_ops dwc3_gadget_ops = {
 	.get_frame		= dwc3_gadget_get_frame,
 	.wakeup			= dwc3_gadget_wakeup,
@@ -2596,6 +2606,7 @@ static const struct usb_gadget_ops dwc3_gadget_ops = {
 	.udc_set_ssp_rate	= dwc3_gadget_set_ssp_rate,
 	.get_config_params	= dwc3_gadget_config_params,
 	.vbus_draw		= dwc3_gadget_vbus_draw,
+	.udc_async_callbacks	= dwc3_gadget_async_callbacks,
 };
 
 /* -------------------------------------------------------------------------- */
@@ -3231,29 +3242,26 @@ static void dwc3_endpoint_interrupt(struct dwc3 *dwc,
 
 static void dwc3_disconnect_gadget(struct dwc3 *dwc)
 {
-	if (dwc->gadget_driver && dwc->gadget_driver->disconnect) {
-		spin_unlock(&dwc->lock);
+	spin_unlock(&dwc->lock);
+	if (dwc->async_callbacks && dwc->gadget_driver->disconnect)
 		dwc->gadget_driver->disconnect(dwc->gadget);
-		spin_lock(&dwc->lock);
-	}
+	spin_lock(&dwc->lock);
 }
 
 static void dwc3_suspend_gadget(struct dwc3 *dwc)
 {
-	if (dwc->gadget_driver && dwc->gadget_driver->suspend) {
-		spin_unlock(&dwc->lock);
+	spin_unlock(&dwc->lock);
+	if (dwc->async_callbacks && dwc->gadget_driver->suspend)
 		dwc->gadget_driver->suspend(dwc->gadget);
-		spin_lock(&dwc->lock);
-	}
+	spin_lock(&dwc->lock);
 }
 
 static void dwc3_resume_gadget(struct dwc3 *dwc)
 {
-	if (dwc->gadget_driver && dwc->gadget_driver->resume) {
-		spin_unlock(&dwc->lock);
+	spin_unlock(&dwc->lock);
+	if (dwc->async_callbacks && dwc->gadget_driver->resume)
 		dwc->gadget_driver->resume(dwc->gadget);
-		spin_lock(&dwc->lock);
-	}
+	spin_lock(&dwc->lock);
 }
 
 static void dwc3_reset_gadget(struct dwc3 *dwc)
@@ -3585,11 +3593,10 @@ static void dwc3_gadget_wakeup_interrupt(struct dwc3 *dwc)
 	 * implemented.
 	 */
 
-	if (dwc->gadget_driver && dwc->gadget_driver->resume) {
-		spin_unlock(&dwc->lock);
+	spin_unlock(&dwc->lock);
+	if (dwc->async_callbacks && dwc->gadget_driver->resume)
 		dwc->gadget_driver->resume(dwc->gadget);
-		spin_lock(&dwc->lock);
-	}
+	spin_lock(&dwc->lock);
 }
 
 static void dwc3_gadget_linksts_change_interrupt(struct dwc3 *dwc,
-- 
2.25.1