linux-kernel - Re: [PATCH 1/2] usb: gadget: r8a66597: Fix two possible sleep-in-atomic-context bugs in init

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Message-ID: <87k1qhevpd.fsf@linux.intel.com>
Date:   Fri, 29 Jun 2018 13:25:02 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     Robert Jarzmik <robert.jarzmik@...e.fr>
Cc:     Jia-Ju Bai <baijiaju1990@...il.com>, gregkh@...uxfoundation.org,
        nicolas.ferre@...rochip.com, keescook@...omium.org,
        allen.lkml@...il.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] usb: gadget: r8a66597: Fix two possible sleep-in-atomic-context bugs in init_controller()


Hi,

Robert Jarzmik <robert.jarzmik@...e.fr> writes:
>>>> The driver may sleep with holding a spinlock.
>>>> The function call paths (from bottom to top) in Linux-4.16.7 are:
>>>>
>>>> [FUNC] msleep
>>>> drivers/usb/gadget/udc/r8a66597-udc.c, 839: 
>>>> 		msleep in init_controller
>>>> drivers/usb/gadget/udc/r8a66597-udc.c, 96: 
>>>> 		init_controller in r8a66597_usb_disconnect
>>>> drivers/usb/gadget/udc/r8a66597-udc.c, 93: 
>>>> 		spin_lock in r8a66597_usb_disconnect
>>>
>>> That should not happen...
>>>
>>> If think the issue you have is that your usb_connect() and usb_disconnect() are
>>> called from interrupt context. I think the proper fix, as what is done in most
>>> udc phys, is to schedule a workqueue, see drivers/usb/phy/phy-gpio-vbus-usb.c,
>>> gpio_vbus_data.vbus.
>>
>> argh, no. No workqueues needed here. Sorry
> Technically why ?

well, strictly technically there's nothing wrong. But it opens a can of
worms. We've seen time and time again drivers growing into
unmaintainable mess because of workqueues being fired in several places.
>
> And as bonus question, why is it better to have mdelay() calls in the driver ?

As a bugfix, it's the smallest fix possible, right? Ideally, we wouldn't
need either of them. Perhaps there's a bit which can be polled instead?

Looking at the code again, it looks like that's messing with
controller's clock and PLL; seems like it should've been done with CCF
anyway.

-- 
balbi