[PATCH] usb: dwc3: Add dwc3 lock for blocking interrupt storming

[JaeHun Jung <jh0801.jung@samsung.com>]

Interrupt Storming occurred with a very low probability of occurrence.
The occurrence of the problem is estimated to be caused by a race condition
between the top half and bottom half of the interrupt service routine.
It was confirmed that variables have values that cannot be held
when ISR occurs through normal H / W irq.
=====================================================================
(struct dwc3_event_buffer *) ev_buf = 0xFFFFFF88DE6A0380 (
	(void *) buf = 0xFFFFFFC01594E000,
	(void *) cache = 0xFFFFFF88DDC14080,
	(unsigned int) length = 4096,
	(unsigned int) lpos = 0,
	(unsigned int) count = 0, <<
	(unsigned int) flags = 1, <<
=====================================================================
"evt->count=0" and "evt->flags=DWC3_EVENT_PENDING" cannot be set
at the same time.

We estimate that a race condition occurred
between dwc3_interrupt() and dwc3_process_event_buf()
called by dwc3_gadget_process_pending_events().
So I try to block the race condition through spin_lock.

Signed-off-by: JaeHun Jung <jh0801.jung@samsung.com>
---
 drivers/usb/dwc3/gadget.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index a0c883f19a41..88f9ecf8cbfe 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -4172,6 +4172,7 @@ static irqreturn_t dwc3_thread_interrupt(int irq, void *_evt)
 static irqreturn_t dwc3_check_event_buf(struct dwc3_event_buffer *evt)
 {
 	struct dwc3 *dwc = evt->dwc;
+	unsigned long flags;
 	u32 amount;
 	u32 count;
 
@@ -4188,13 +4189,18 @@ static irqreturn_t dwc3_check_event_buf(struct dwc3_event_buffer *evt)
 	 * irq event handler completes before caching new event to prevent
 	 * losing events.
 	 */
-	if (evt->flags & DWC3_EVENT_PENDING)
+	spin_lock_irqsave(&dwc->lock, flags);
+	if (evt->flags & DWC3_EVENT_PENDING) {
+		spin_unlock_irqrestore(&dwc->lock, flags);
 		return IRQ_HANDLED;
+	}
 
 	count = dwc3_readl(dwc->regs, DWC3_GEVNTCOUNT(0));
 	count &= DWC3_GEVNTCOUNT_MASK;
-	if (!count)
+	if (!count) {
+		spin_unlock_irqrestore(&dwc->lock, flags);
 		return IRQ_NONE;
+	}
 
 	evt->count = count;
 	evt->flags |= DWC3_EVENT_PENDING;
@@ -4210,6 +4216,7 @@ static irqreturn_t dwc3_check_event_buf(struct dwc3_event_buffer *evt)
 		memcpy(evt->cache, evt->buf, count - amount);
 
 	dwc3_writel(dwc->regs, DWC3_GEVNTCOUNT(0), count);
+	spin_unlock_irqrestore(&dwc->lock, flags);
 
 	return IRQ_WAKE_THREAD;
 }
-- 
2.31.1