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

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Date:	Mon, 26 Jul 2010 10:47:16 -0400
From:	Elly Jones <ellyjones@...gle.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: Re: [patch] usbnet: fix 100% CPU use on suspended device

On Mon, Jul 26, 2010 at 10:36 AM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Mon, 26 Jul 2010, Elly Jones wrote:
>
>> On Mon, Jul 26, 2010 at 12:57 AM, David Miller <davem@...emloft.net> wrote:
>> > From: Elly Jones <ellyjones@...gle.com>
>> > Date: Wed, 21 Jul 2010 14:51:48 -0400
>> >
>> >> Subject: [patch] usbnet: fix 100% CPU use on suspended device
>> >> From: Elly Jones <ellyjones@...gle.com>
>> >>
>> >> This patch causes the usbnet module not to attempt to submit URBs to the device
>> >> if the device is not ready to accept them. This fixes a misbehavior trigged by
>> >> the Qualcomm Gobi driver (released under GPL through their Code Aurora
>> >> initiative) which causes the usbnet core to consume 100% of CPU attempting and
>> >> failing to submit URBs. This patch is against Linus's 2.6 repo commit
>> >> a9f7f2e74ae0e6a801a2433dc8e9124d73da0cb4.
>> >> Signed-off-by: Elizabeth Jones <ellyjones@...gle.com>
>> >
>> > If the Qualcomm Gobi driver is the only one where this happens, maybe the
>> > real problem is in that driver.
>>
>> The member in question (dev->udev->can_submit) is documented as 'URBs
>> may be submitted'. The existing code doesn't honor that flag. It is
>> somewhat puzzling that (so far) only the Gobi driver seems to use that
>> flag, but I don't think the bug lies in their driver here.
>
> That flag is not intended for use by drivers but by the USB core.  (It
> gets cleared only when the device is suspended.)  usbnet and Gobi
> shouldn't need to look at it.

Aha!

>> > I'm not applying this until a USB person looks more deeply into this.
>>
>> Alright. Can you suggest a particular USB person to bother?
>>
>> >> ---
>> >> diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
>> >> index 81c76ad..df7e72e 100644
>> >> --- a/drivers/net/usb/usbnet.c
>> >> +++ b/drivers/net/usb/usbnet.c
>> >> @@ -1172,6 +1172,7 @@ static void usbnet_bh (unsigned long param)
>> >>       // or are we maybe short a few urbs?
>> >>       } else if (netif_running (dev->net) &&
>> >>                  netif_device_present (dev->net) &&
>> >> +                dev->udev->can_submit &&
>> >>                  !timer_pending (&dev->delay) &&
>> >>                  !test_bit (EVENT_RX_HALT, &dev->flags)) {
>> >>               int     temp = dev->rxq.qlen;
>
> 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?

> Alan Stern

-- Elly
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