netdev - Re: [PATCH 4.4 18/31] r8152: napi hangup fix after disconnect

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Message-ID: <1536778472.3024.204.camel@codethink.co.uk>
Date:   Wed, 12 Sep 2018 19:54:32 +0100
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Jiri Slaby <jslaby@...e.cz>, linux-usb@...r.kernel.org,
        netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Cc:     stable@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4.4 18/31] r8152: napi hangup fix after disconnect

On Sat, 2018-08-25 at 09:43 +0200, Jiri Slaby wrote:
> On 08/24/2018, 06:38 PM, Ben Hutchings wrote:
> > On Fri, 2018-07-20 at 14:13 +0200, Greg Kroah-Hartman wrote:
> > > 4.4-stable review patch.  If anyone has any objections, please let me know.
> > > 
> > > ------------------
> > > 
> > > From: Jiri Slaby <jslaby@...e.cz>
> > > 
> > > [ Upstream commit 0ee1f4734967af8321ecebaf9c74221ace34f2d5 ]
> > 
> > [...]
> > > --- a/drivers/net/usb/r8152.c
> > > +++ b/drivers/net/usb/r8152.c
> > > @@ -3139,7 +3139,8 @@ static int rtl8152_close(struct net_devi
> > >  #ifdef CONFIG_PM_SLEEP
> > >  	unregister_pm_notifier(&tp->pm_notifier);
> > >  #endif
> > > -	napi_disable(&tp->napi);
> > > +	if (!test_bit(RTL8152_UNPLUG, &tp->flags))
> > > +		napi_disable(&tp->napi);
> > >  	clear_bit(WORK_ENABLE, &tp->flags);
> > >  	usb_kill_urb(tp->intr_urb);
> > >  	cancel_delayed_work_sync(&tp->schedule);
> > 
> > This flag appears to be set only if the USB device is actually
> > disconnected.  In case the driver is unbound for some other reason
> > (like the module is removed), the same problem will occur.
> 
> Could you elaborate? I thought this would happen:
> module_exit -> usb_deregister -> usb_unbind_device -> rtl8152_disconnect
> -> unregister_netdev -> rtl8152_close
> 
> Am I missing something?

What I mean is that if the USB device has not been *physically*
disconnected then its usb_device::state will not be
USB_STATE_NOTATTACHED.  So rtl8152_disconnect() will not set the
RTL8152_UNPLUG flag and rtl8152_close() will still call napi_disable()
which will hang.

Some options to fix this:
- Add a separate flag which rtl8152_close() checks and
rtl8152_disconnect() always sets
- Call dev_close() before netif_napi_del()

Ben.

-- 
Ben Hutchings, Software Developer                         Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
                                     Manchester, M1 2HF, United Kingdom