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

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Date:   Fri, 29 Jun 2018 08:48:46 +0200
From:   Robert Jarzmik <robert.jarzmik@...e.fr>
To:     Felipe Balbi <balbi@...nel.org>
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()

Felipe Balbi <balbi@...nel.org> writes:

> Hi,
>
> Robert Jarzmik <robert.jarzmik@...e.fr> writes:
>
>> Jia-Ju Bai <baijiaju1990@...il.com> 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 ?

And as bonus question, why is it better to have mdelay() calls in the driver ?

Cheers.

-- 
Robert