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

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Message-ID: <AANLkTim-6VhV7AD_QQh-5j5RqxEDDh1oyX4CqZWGb-ZH@mail.gmail.com>
Date:	Wed, 4 Aug 2010 10:04:48 -0400
From:	Elly Jones <ellyjones@...gle.com>
To:	Oliver Neukum <oliver@...kum.org>
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

On Tue, Aug 3, 2010 at 10:39 AM, Oliver Neukum <oliver@...kum.org> wrote:
> 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.

'Give up' meaning what? If we reschedule the tasklet, it'll just try
again (and fail again), won't it?

>        Regards
>                Oliver

-- Elly
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