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

[정재훈]

Hi.

> -----Original Message-----
> From: Thinh Nguyen [mailto:Thinh.Nguyen@xxxxxxxxxxxx]
> Sent: Thursday, March 10, 2022 11:14 AM
> To: JaeHun Jung; Felipe Balbi; Greg Kroah-Hartman
> Cc: open list:USB XHCI DRIVER; open list; Seungchull Suh; Daehwan Jung
> 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?
Maybe it could be. But "evt->count = 0;" is updated on dwc3_process_event_buf().
So, I think spin_lock is more clear routine for this issue.

> 
> 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