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Date:	Mon, 26 Jul 2010 09:26:59 -0400
From:	Elly Jones <ellyjones@...gle.com>
To:	David Miller <davem@...emloft.net>
Cc:	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 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.

> 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;
>> --
>

-- Elly
--
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