From: Felipe Balbi <balbi@kernel.org>
To: Robert Jarzmik <robert.jarzmik@free.fr>
Cc: Jia-Ju Bai <baijiaju1990@gmail.com>,
gregkh@linuxfoundation.org, nicolas.ferre@microchip.com,
keescook@chromium.org, allen.lkml@gmail.com,
linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] usb: gadget: r8a66597: Fix two possible sleep-in-atomic-context bugs in init_controller()
Date: Fri, 29 Jun 2018 13:25:02 +0300 [thread overview]
Message-ID: <87k1qhevpd.fsf@linux.intel.com> (raw)
In-Reply-To: <87efgqkrzl.fsf@belgarion.home>
Hi,
Robert Jarzmik <robert.jarzmik@free.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
next prev parent reply other threads:[~2018-06-29 10:27 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-20 3:54 [PATCH 1/2] usb: gadget: r8a66597: Fix two possible sleep-in-atomic-context bugs in init_controller() Jia-Ju Bai
2018-06-21 9:06 ` Robert Jarzmik
2018-06-29 6:35 ` Felipe Balbi
2018-06-29 6:48 ` Robert Jarzmik
2018-06-29 10:25 ` Felipe Balbi [this message]
2018-06-29 11:04 ` Robert Jarzmik
2018-06-29 11:15 ` Felipe Balbi
2018-06-29 13:21 ` Robert Jarzmik
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