linux-kernel - Re: [PATCH] usb: dwc3: gadget: Avoid race between dwc3 interrupt handler and irq thread handler

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Message-ID: <871swt3a1e.fsf@linux.intel.com>
Date:   Tue, 27 Dec 2016 13:07:25 +0200
From:   Felipe Balbi <balbi@...nel.org>
To:     Janusz Dziedzic <janusz.dziedzic@...il.com>,
        Baolin Wang <baolin.wang@...aro.org>
Cc:     gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, linaro-kernel@...ts.linaro.org,
        broonie@...nel.org
Subject: Re: [PATCH] usb: dwc3: gadget: Avoid race between dwc3 interrupt handler and irq thread handler


Hi,

Janusz Dziedzic <janusz.dziedzic@...il.com> writes:
> 2016-12-26 9:01 GMT+01:00 Baolin Wang <baolin.wang@...aro.org>:
>> On some platfroms(like x86 platform), when one core is running the USB gadget
>> irq thread handler by dwc3_thread_interrupt(), meanwhile another core also can
>> respond other interrupts from dwc3 controller and modify the event buffer by
>> dwc3_interrupt() function, that will cause getting the wrong event count in
>> irq thread handler to make the USB function abnormal.
>>
>> We should add spin_lock/unlock() in dwc3_check_event_buf() to avoid this race.
>>
> Interesting, I always think we mask interrupt in dwc3_interrupt() by setting
> DWC3_GEVNTSIZ_INTMASK
> And unmask interrupt when we end dwc3_thread_interrupt().
>
> So, we shouldn't get any IRQ from HW during dwc3_thread_interrupt(),
> or I miss something?
> Do you have some traces that indicate this masking will not work correctly?

that's the very question I have. We are already masking interrupts from
this controller. The only thing this could race with is usb_ep_queue(),
but that gets nowhere close to anything we're doing in the top half
handler, so there's really no danger of anything bad happening.

I'd like to see traces as well.

-- 
balbi

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