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Date: Mon, 2 Oct 2023 16:53:05 +0200
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= <u.kleine-koenig@pengutronix.de>
Cc: Chunfeng Yun <chunfeng.yun@mediatek.com>, linux-usb@vger.kernel.org,
	linux-mediatek@lists.infradead.org, kernel@pengutronix.de
Subject: Re: [PATCH v2] usb: mtu3: Convert to platform remove callback
 returning void
Message-ID: <2023100253-amino-pencil-9a96@gregkh>
References: <20230914200251.919584-1-u.kleine-koenig@pengutronix.de>
 <2023100219-variety-genre-befe@gregkh>
 <20231002144959.jc6wwfrvwd4cyu2l@pengutronix.de>
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In-Reply-To: <20231002144959.jc6wwfrvwd4cyu2l@pengutronix.de>

On Mon, Oct 02, 2023 at 04:49:59PM +0200, Uwe Kleine-König wrote:
> Hello Greg,
> 
> On Mon, Oct 02, 2023 at 04:39:47PM +0200, Greg Kroah-Hartman wrote:
> > On Thu, Sep 14, 2023 at 10:02:51PM +0200, Uwe Kleine-König wrote:
> > > @@ -469,8 +469,17 @@ static int mtu3_remove(struct platform_device *pdev)
> > >  		ssusb_gadget_exit(ssusb);
> > >  		ssusb_host_exit(ssusb);
> > >  		break;
> > > -	default:
> > > -		return -EINVAL;
> > > +	case USB_DR_MODE_UNKNOWN:
> > > +		/*
> > > +		 * This cannot happen because with dr_mode ==
> > > +		 * USB_DR_MODE_UNKNOWN, .probe() doesn't succeed and so
> > > +		 * .remove() wouldn't be called at all. However (little
> > > +		 * surprising) the compiler isn't smart enough to see that, so
> > > +		 * we explicitly have this case item to not make the compiler
> > > +		 * wail about an unhandled enumeration value.
> > > +		 */
> > > +		WARN_ON(1);
> > 
> > Please don't add new WARN_ON() calls to the kernel, print out a big
> > error message and return, don't reboot the machine.
> 
> Huh, printing out an loud error message was my intention. It's news to
> me that WARN_ON() reboots the machine?! I thought BUG_ON() was the one
> with the effects you describe that I shouldn't use.

panic-on-warn is set for zillions[1] of Linux systems out there, so systems
will reboot.

thanks,

greg k-h

[1] Unofficial number, I know the "cloud" systems set this, as well as
    all of Samsung's phone kernels, a non-trivial amount of Linux
    instances in the wild.