From: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
To: 정재훈 <jh0801.jung@samsung.com>,
"Thinh Nguyen" <Thinh.Nguyen@synopsys.com>,
"'Felipe Balbi'" <balbi@kernel.org>,
"'Greg Kroah-Hartman'" <gregkh@linuxfoundation.org>
Cc: "'open list:USB XHCI DRIVER'" <linux-usb@vger.kernel.org>,
'open list' <linux-kernel@vger.kernel.org>,
'Seungchull Suh' <sc.suh@samsung.com>,
'Daehwan Jung' <dh10.jung@samsung.com>,
"cpgs@samsung.com" <cpgs@samsung.com>,
"cpgsproxy5@samsung.com" <cpgsproxy5@samsung.com>
Subject: Re: [PATCH] usb: dwc3: Add dwc3 lock for blocking interrupt storming
Date: Fri, 11 Mar 2022 01:56:38 +0000 [thread overview]
Message-ID: <559b00b6-8b3d-9422-6a25-674f719ad237@synopsys.com> (raw)
In-Reply-To: <016a01d834e7$72b11fd0$58135f70$@samsung.com>
정재훈 wrote:
> Hi.
>
>> -----Original Message-----
>> From: Thinh Nguyen [mailto:Thinh.Nguyen@synopsys.com]
>> 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.
>
Not really. If problem is due to the evt->flags not updated in time,
then the solution should be using the memory barrier. The spin_lock
would obfuscate the issue. And we should avoid using spin_lock in the
top-half.
BR,
Thinh
>>
>> 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
>
next prev parent reply other threads:[~2022-03-11 1:57 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20220307052605epcas2p2b84f6db2642863ed61373070f508e200@epcas2p2.samsung.com>
2022-03-07 5:24 ` [PATCH] usb: dwc3: Add dwc3 lock for blocking interrupt storming JaeHun Jung
2022-03-10 2:13 ` Thinh Nguyen
2022-03-11 1:29 ` 정재훈
2022-03-11 1:56 ` Thinh Nguyen [this message]
2022-03-11 2:43 ` 정재훈
2022-03-11 3:51 ` Thinh Nguyen
2022-03-11 3:55 ` Thinh Nguyen
2022-03-11 5:01 ` 정재훈
2022-03-14 23:18 ` Thinh Nguyen
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