netdev - Re: [patch] usbnet: fix 100% CPU use on suspended device

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Message-Id: <201008031639.24874.oliver@neukum.org>
Date:	Tue, 3 Aug 2010 16:39:24 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	Elly Jones <ellyjones@...gle.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	USB list <linux-usb@...r.kernel.org>
Subject: Re: [patch] usbnet: fix 100% CPU use on suspended device

Am Montag, 2. August 2010, 15:31:33 schrieb Elly Jones:
> On Mon, Jul 26, 2010 at 12:21 PM, Oliver Neukum <oliver@...kum.org> wrote:
> > Am Montag, 26. Juli 2010, 17:13:23 schrieb Alan Stern:
> >> On Mon, 26 Jul 2010, Elly Jones wrote:
> >>
> >> > > This isn't right.  The problem should be fixed some other way.  Under
> >> > > what circumstances are URBs submitted incorrectly?
> >> >
> >> > When the device is autosuspended. What is the proper thing for a
> >> > device to do here?
> >>
> >> From looking at the code, it appears that the EVENT_DEV_ASLEEP flag
> >> should be tested in usbnet_bh() the way it is in rx_submit().  But I'm
> >> not an expert on usbnet; we should ask someone who is, like Oliver.
> >
> > Sorry, I didn't notice this thread.
> >
> > The correct way to check for autosuspend in usbnet is to look
> > at EVENT_DEV_ASLEEP under txq.lock. That being said, usbnet_bh()
> > uses rx_submit() which does the correct check. The bug seems to be
> > a lack of error handling in usbnet_bh() regarding the return of rx_submit()
> 
> If rx_submit() fails, should usbnet_bh() just not tasklet_schedule() itself?

That would not work unless the cause of the failure would be removed.
If you get -ENOLINK the sane option seems to me to give up.

	Regards
		Oliver
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