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Date:   Tue, 3 Sep 2019 13:17:07 -0400 (EDT)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     David Howells <dhowells@redhat.com>
cc:     Guenter Roeck <linux@roeck-us.net>, <viro@zeniv.linux.org.uk>,
        Casey Schaufler <casey@schaufler-ca.com>,
        Stephen Smalley <sds@tycho.nsa.gov>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        <nicolas.dichtel@6wind.com>, <raven@themaw.net>,
        Christian Brauner <christian@brauner.io>,
        <keyrings@vger.kernel.org>, <linux-usb@vger.kernel.org>,
        <linux-security-module@vger.kernel.org>,
        <linux-fsdevel@vger.kernel.org>, <linux-api@vger.kernel.org>,
        <linux-block@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 08/11] usb: Add USB subsystem notifications [ver #7]
In-Reply-To: <Pine.LNX.4.44L0.1909031303500.1859-100000@iolanthe.rowland.org>
Message-ID: <Pine.LNX.4.44L0.1909031316130.1859-100000@iolanthe.rowland.org>
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On Tue, 3 Sep 2019, Alan Stern wrote:

> On Tue, 3 Sep 2019, David Howells wrote:
> 
> > Guenter Roeck <linux@roeck-us.net> wrote:
> > 
> > > > > This added call to usbdev_remove() results in a crash when running
> > > > > the qemu "tosa" emulation. Removing the call fixes the problem.
> > > > 
> > > > Yeah - I'm going to drop the bus notification messages for now.
> > > > 
> > > It is not the bus notification itself causing problems. It is the
> > > call to usbdev_remove().
> > 
> > Unfortunately, I don't know how to fix it and don't have much time to
> > investigate it right now - and it's something that can be added back later.
> 
> The cause of your problem is quite simple:
> 
>  static int usbdev_notify(struct notifier_block *self,
>  			       unsigned long action, void *dev)
>  {
>  	switch (action) {
>  	case USB_DEVICE_ADD:
> +		post_usb_device_notification(dev, NOTIFY_USB_DEVICE_ADD, 0);
>  		break;
>  	case USB_DEVICE_REMOVE:
> +		post_usb_device_notification(dev, NOTIFY_USB_DEVICE_REMOVE, 0);
> +		usbdev_remove(dev);
> +		break;
> +	case USB_BUS_ADD:
> +		post_usb_bus_notification(dev, NOTIFY_USB_BUS_ADD, 0);
> +		break;
> +	case USB_BUS_REMOVE:
> +		post_usb_bus_notification(dev, NOTIFY_USB_BUS_REMOVE, 0);
>  		usbdev_remove(dev);
>  		break;
>  	}
> 
> The original code had usbdev_remove(dev) under the USB_DEVICE_REMOVE
> case.  The patch mistakenly moves it, putting it under the
------------------------------^^^^^

Sorry, I should have said "duplicates" it.

Alan Stern

> USB_BUS_REMOVE case.
> 
> If the usbdev_remove() call were left where it was originally, the 
> problem would be solved.
> 
> Alan Stern