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

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Date:   Thu, 29 Dec 2016 01:29:49 +0000
From:   John Youn <John.Youn@...opsys.com>
To:     Felipe Balbi <balbi@...nel.org>,
        Janusz Dziedzic <janusz.dziedzic@...il.com>
CC:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Baolin Wang <baolin.wang@...aro.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        USB <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
        Mark Brown <broonie@...nel.org>
Subject: RE: [PATCH] usb: dwc3: gadget: Avoid race between dwc3 interrupt
 handler and irq thread handler



> -----Original Message-----
> From: linux-usb-owner@...r.kernel.org [mailto:linux-usb-
> owner@...r.kernel.org] On Behalf Of Felipe Balbi
> Sent: Wednesday, December 28, 2016 8:19 AM
> To: Janusz Dziedzic <janusz.dziedzic@...il.com>
> Cc: Lu Baolu <baolu.lu@...ux.intel.com>; Baolin Wang
> <baolin.wang@...aro.org>; Greg KH <gregkh@...uxfoundation.org>; USB
> <linux-usb@...r.kernel.org>; LKML <linux-kernel@...r.kernel.org>; Linaro
> Kernel Mailman List <linaro-kernel@...ts.linaro.org>; Mark Brown
> <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:
> >>>> 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.
> >>>
> >>> Why not spin_lock_irq ones? This lock seems to be used in both
> >>> normal and interrupt threads. Or, I missed anything?
> >>
> >> this is top half handler. Interrupts are already disabled.
> >>
> > BTW,
> > We don't use spin_lock in top half handler.
> > Maybe we should/can switch all spin_lock_irqsave() to simple
> > spin_lock() in the thread/callbacks?
> 
> in theory, yes we've masked all interrupts from this controller for the
> duration of the thread handler. However this breaks networking
> gadgets. I can only guess network stack has a hard requirement to run
> with IRQs disabled.
> 

Hi,

Is this version 3.00a of the core?

That version has a STAR where the interrupts cannot be masked. That results in similar symptoms to what you're seeing here.

Regards,
John