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

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Date:	Tue, 05 Mar 2013 18:35:31 +0100
From:	Bjørn Mork <bjorn@...k.no>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Ming Lei <ming.lei@...onical.com>,
	"David S. Miller" <davem@...emloft.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Kosina <jkosina@...e.cz>, 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

Alan Stern <stern@...land.harvard.edu> writes:
> On Tue, 5 Mar 2013, Bjørn Mork wrote:
>> 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.
>
> Mainly for historical reasons.  System suspend existed long before 
> runtime suspend did.  When runtime suspend was added, it piggybacked 
> off the existing code.  Furthermore, originally there was no 
> requirement that system suspend always succeed; that was added later.
>
> Also, the code paths are not completely different.  They differ mainly 
> in their error handling.  But when you think about it, how serious an 
> error can you encounter when you try to _stop_ using a device?

Thanks for explaining.

>> 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.
>
> You are welcome to submit a patch to do this.  It shouldn't be hard; we
> already have a flag indicating that an interface needs to be unbound at
> reprobed at resume time.  You can update the kerneldoc in addition; as
> you noticed, it currently does not describe the actual code completely
> accurately.

I guess I saw that coming :)  Will take a shot at it when time permits.


Bjørn
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