linux-kernel - Re: [PATCH] usb: dwc3: Add dwc3 lock for blocking interrupt storming

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Message-ID: <99eabe6c-8782-1bc6-e1d7-09b019cee65b@synopsys.com>
Date:   Thu, 10 Mar 2022 02:13:53 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     JaeHun Jung <jh0801.jung@...sung.com>,
        Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     "open list:USB XHCI DRIVER" <linux-usb@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Seungchull Suh <sc.suh@...sung.com>,
        Daehwan Jung <dh10.jung@...sung.com>
Subject: Re: [PATCH] usb: dwc3: Add dwc3 lock for blocking interrupt storming

Hi,

JaeHun Jung wrote:
> 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.

This looks like it needs a memory barrier. Would this work for you?

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index c02e239978e0..a96c344b9f17 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -5340,6 +5340,9 @@ static irqreturn_t dwc3_check_event_buf(struct dwc3_event_buffer *evt)
                return IRQ_HANDLED;
        }
 
+       /* Make sure the event flags is updated */
+       wmb();
+
        /*
         * With PCIe legacy interrupt, test shows that top-half irq handler can
         * be called again after HW interrupt deassertion. Check if bottom-half


Thanks,
Thinh