netdev - Re: [PATCH 4/7] usbnet: cdc_mbim: don't recover device if suspend fails in system sleep

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Message-ID: <87wqtlommw.fsf@nemi.mork.no>
Date:	Tue, 05 Mar 2013 17:08:07 +0100
From:	Bjørn Mork <bjorn@...k.no>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oneukum@...e.de>, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org, linux-input@...r.kernel.org
Subject: Re: [PATCH 4/7] usbnet: cdc_mbim: don't recover device if suspend fails in system sleep

Ming Lei <ming.lei@...onical.com> writes:

> Yes, USB core will flush any outstanding URBs, but the driver still need
> to deal with suspend failure carefully, for example, suppose usb_resume()
> is called in suspend failure path, and the submitted URBs are killed
> by USB core later. But after the device is wakeup, and the resume() will
> do nothing since the suspend count is leaked. So it is what the patches
> are fixing, and it is better to not depend on the default flushing URBs of
> USB core.

I am starting to wonder why the USB core has combined system suspend and
runtime suspend if we are going to end up with every driver testing
PMSG_IS_AUTO(message) and selecting a completely different code path.

You are right that we will end up with problems if usbnet_resume is
called for a device usbnet hasn't suspended.  But I'd still claim that
is a bug in the USB core, which is the one that decided to ignore the
suspend error and still call resume.

I guess proper error handling here require the USB core to see the
interface driver as dead if it fails to suspend on system suspend, and
do forced rebinding on resume.

I am not going to fight this any longer.  The per-driver
PMSG_IS_AUTO(message) testing is an ugly workround for a core problem,
but they are already all over the place...  Still, please make sure the
drivers all return 0 if they are pretending to suspend. No error code
return if the driver ignores the error.

Bjørn
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