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Message-ID: <20240809234227.eriwy5e6leatzdyh@synopsys.com>
Date: Fri, 9 Aug 2024 23:42:46 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Selvarasu Ganesan <selvarasu.g@...sung.com>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"jh0801.jung@...sung.com" <jh0801.jung@...sung.com>,
"dh10.jung@...sung.com" <dh10.jung@...sung.com>,
"naushad@...sung.com" <naushad@...sung.com>,
"akash.m5@...sung.com" <akash.m5@...sung.com>,
"rc93.raju@...sung.com" <rc93.raju@...sung.com>,
"taehyun.cho@...sung.com" <taehyun.cho@...sung.com>,
"hongpooh.kim@...sung.com" <hongpooh.kim@...sung.com>,
"eomji.oh@...sung.com" <eomji.oh@...sung.com>,
"shijie.cai@...sung.com" <shijie.cai@...sung.com>
Subject: Re: [PATCH] usb: dwc3: Potential fix of possible dwc3 interrupt storm
On Thu, Aug 08, 2024, Selvarasu Ganesan wrote:
>
> On 8/8/2024 6:45 AM, Thinh Nguyen wrote:
> > On Wed, Aug 07, 2024, Selvarasu Ganesan wrote:
> >> On 8/7/2024 6:08 AM, Thinh Nguyen wrote:
> >>> On Fri, Jul 19, 2024, Selvarasu Ganesan wrote:
> >>>> In certain scenarios, there is a chance that the CPU may not be
> >>>> scheduled the bottom half of dwc3 interrupt. This is because the CPU
> >>>> may hang up where any work queue lockup has happened for the same CPU
> >>>> that is trying to schedule the dwc3 thread interrupt. In this scenario,
> >>>> the USB can enter runtime suspend as the bus may idle for a longer time
> >>>> , or user can reconnect the USB cable. Then, the dwc3 event interrupt
> >>>> can be enabled when runtime resume is happening with regardless of the
> >>>> previous event status. This can lead to a dwc3 IRQ storm due to the
> >>>> return from the interrupt handler by checking only the evt->flags as
> >>>> DWC3_EVENT_PENDING, where the same flag was set as DWC3_EVENT_PENDING
> >>>> in previous work queue lockup.
> >>>> Let's consider the following sequences in this scenario,
> >>>>
> >>>> Call trace of dwc3 IRQ after workqueue lockup scenario
> >>>> ======================================================
> >>>> IRQ #1:
> >>>> ->dwc3_interrupt()
> >>>> ->dwc3_check_event_buf()
> >>>> ->if (evt->flags & DWC3_EVENT_PENDING)
> >>>> return IRQ_HANDLED;
> >>>> ->evt->flags |= DWC3_EVENT_PENDING;
> >>>> ->/* Disable interrupt by setting DWC3_GEVNTSIZ_INTMASK in
> >>>> DWC3_GEVNTSIZ
> >>>> ->return IRQ_WAKE_THREAD; // No workqueue scheduled for dwc3
> >>>> thread_fu due to workqueue lockup
> >>>> even after return IRQ_WAKE_THREAD
> >>>> from top-half.
> >>>>
> >>>> Thread #2:
> >>>> ->dwc3_runtime_resume()
> >>>> ->dwc3_resume_common()
> >>>> ->dwc3_gadget_resume()
> >>>> ->dwc3_gadget_soft_connect()
> >>>> ->dwc3_event_buffers_setup()
> >>>> ->/*Enable interrupt by clearing DWC3_GEVNTSIZ_INTMASK in
> >>>> DWC3_GEVNTSIZ*/
> >>>>
> >>>> Start IRQ Storming after enable dwc3 event in resume path
> >>>> =========================================================
> >>>> CPU0: IRQ
> >>>> dwc3_interrupt()
> >>>> dwc3_check_event_buf()
> >>>> if (evt->flags & DWC3_EVENT_PENDING)
> >>>> return IRQ_HANDLED;
> >>>>
> >>>> CPU0: IRQ
> >>>> dwc3_interrupt()
> >>>> dwc3_check_event_buf()
> >>>> if (evt->flags & DWC3_EVENT_PENDING)
> >>>> return IRQ_HANDLED;
> >>>> ..
> >>>> ..
> >>>>
> >>>> To fix this issue by avoiding enabling of the dwc3 event interrupt in
> >>>> the runtime resume path if dwc3 event processing is in progress.
> >>>>
> >>>> Signed-off-by: Selvarasu Ganesan <selvarasu.g@...sung.com>
> >>>> ---
> >>>> drivers/usb/dwc3/core.c | 8 ++++++--
> >>>> 1 file changed, 6 insertions(+), 2 deletions(-)
> >>>>
> >>>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> >>>> index cb82557678dd..610792a70805 100644
> >>>> --- a/drivers/usb/dwc3/core.c
> >>>> +++ b/drivers/usb/dwc3/core.c
> >>>> @@ -549,8 +549,12 @@ int dwc3_event_buffers_setup(struct dwc3 *dwc)
> >>>> lower_32_bits(evt->dma));
> >>>> dwc3_writel(dwc->regs, DWC3_GEVNTADRHI(0),
> >>>> upper_32_bits(evt->dma));
> >>>> - dwc3_writel(dwc->regs, DWC3_GEVNTSIZ(0),
> >>>> - DWC3_GEVNTSIZ_SIZE(evt->length));
> >>>> +
> >>>> + /* Skip enable dwc3 event interrupt if event is processing in middle */
> >>>> + if (!(evt->flags & DWC3_EVENT_PENDING))
> >>>> + dwc3_writel(dwc->regs, DWC3_GEVNTSIZ(0),
> >>>> + DWC3_GEVNTSIZ_SIZE(evt->length));
> >>>> +
> >>>> dwc3_writel(dwc->regs, DWC3_GEVNTCOUNT(0), 0);
> >>>>
> >>>> return 0;
> >>>> --
> >>>> 2.17.1
> >>>>
> >>> We're not waking up from a hibernation. So after a soft-reset and
> >>> resume, the events that weren't processed are stale. They should be
> >>> processed prior to entering suspend or be discarded before resume.
> >>>
> >>> The synchronize_irq() during suspend() was not sufficient to prevent
> >>> this? What are we missing here.
> >>>
> >>> Thanks,
> >>> Thinh
> >> I don’t think the triggering of interrupt would not be stopped even if
> >> do soft reset. It's because of event count is may be valid .
> > Ok. I think I see what you're referring to when you say "event is
> > processing in the middle" now.
> >
> > What you want to check is probably this in dwc3_event_buffers_setup().
> > Please confirm:
> >
> > if (dwc->pending_events)
> > dwc3_writel(dwc->regs, DWC3_GEVNTSIZ(0),
> > DWC3_GEVNTSIZ_INTMASK | DWC3_GEVNTSIZ_SIZE(evt->length));
> > else
> > dwc3_writel(dwc->regs, DWC3_GEVNTSIZ(0), DWC3_GEVNTSIZ_SIZE(evt->length));
>
> Yes, we are expecting the same. But, we must verify the status of
> evt->flags, which will indicate whether the event is currently
> processing in middle or not. The below code is for the reference.
>
> if (!(evt->flags & DWC3_EVENT_PENDING))
> dwc3_writel(dwc->regs, DWC3_GEVNTSIZ(0),
> DWC3_GEVNTSIZ_SIZE(evt->length));
> else
> dwc3_writel(dwc->regs, DWC3_GEVNTSIZ(0),
> DWC3_GEVNTSIZ_INTMASK | DWC3_GEVNTSIZ_SIZE(evt->length));
So, this happens while pending_events is set right? I need to review
this runtime suspend flow next week. Something doesn't look right. When
there's a suspend/resume runtime or not, there's a soft disconnect. We
shouldn't be processing any event prior to going into suspend. Also, we
shouldn't be doing soft-disconnect while connected and in operation
unless we specifically tell it to.
>
> >> Let consider the scenarios where SW is not acknowledge the event count
> >> after getting a interrupt with disable GEVNTSIZ_INTMASK =0. It will
> >> triggering the spurious interrupts until enable GEVNTSIZ_INTMASK=1 or
> >> acknowledge the event count by SW. This is happening here because of We
> >> just return from interrupt handler by checking if evt->flags as
> >> DWC3_EVENT_PENDING. Clearing of DWC3_EVENT_PENDING flag is done in
> >> dwc3_thread_interrupt. In some scenario it's not happening due to cpu
> >> hangup or work queue lockup.
> > This can be mitigated by adjusting the imod_interval (interrupt
> > moderation). Have you tried that?
>
>
> Yes we tried to play around the changing of imod interval value but no
> improvements.
Ok.
Thanks,
Thinh
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