linux-kernel - Re: [PATCH] USB: cdc-acm: fix broken runtime suspend

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Date:	Tue, 15 Apr 2014 14:19:08 +0200
From:	Johan Hovold <jhovold@...il.com>
To:	Oliver Neukum <oneukum@...e.de>
Cc:	Johan Hovold <jhovold@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org, Peter Hurley <peter@...leysoftware.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Xiao Jin <jin.xiao@...el.com>, david.a.cohen@...ux.intel.com,
	yanmin.zhang@...el.com
Subject: Re: [PATCH] USB: cdc-acm: fix broken runtime suspend

On Tue, Apr 15, 2014 at 11:13:17AM +0200, Johan Hovold wrote:
> On Tue, Apr 15, 2014 at 10:35:19AM +0200, Oliver Neukum wrote:
> > On Mon, 2014-04-14 at 21:58 +0200, Johan Hovold wrote:
> > 
> > > Fix this by implementing a delayed-write queue using urb anchors and
> > > making sure to discard the queue properly at shutdown.
> > 
> > Looks very good, with one exception: acm_tty_close() must
> > synchronously resume the device so that the anchor is emptied
> > before ASYNCB is cleared.
> 
> That isn't necessary as the device is already about to be resumed and
> the initialised flag will not be cleared until chars_in_buffer() returns
> 0 or closing wait times out.
> 
> In the first case, the queue has been emptied as the urbs are submitted
> at resume(), and in the second case the queue is discarded at
> shutdown().

Turns out that the usb_wwan (and thus ipw, option, and qcserial) and
sierra usb-serial drivers also fail to get runtime-suspend right. The
first one leaks urbs and the second does synchronous resume and submits
urbs during shutdown.

I'll fix it up.

Johan
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