linux-kernel - Re: [PATCH] USB: EHCI: fix for leaking isochronous data

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Message-ID: <514B86A9.60401@web.de>
Date:	Thu, 21 Mar 2013 23:16:09 +0100
From:	Soeren Moch <smoch@....de>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Andrew Lunn <andrew@...n.ch>, Arnd Bergmann <arnd@...db.de>,
	USB list <linux-usb@...r.kernel.org>,
	Jason Cooper <jason@...edaemon.net>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	linux-mm@...ck.org,
	Kernel development list <linux-kernel@...r.kernel.org>,
	linux-arm-kernel@...ts.infradead.org, michael@...rulasolutions.com
Subject: Re: [PATCH] USB: EHCI: fix for leaking isochronous data

On 21.03.2013 22:20, Andrew Lunn wrote:
> On Thu, Mar 21, 2013 at 05:12:01PM -0400, Alan Stern wrote:
>> On Thu, 21 Mar 2013, Alan Stern wrote:
>>
>>> On Thu, 21 Mar 2013, Soeren Moch wrote:
>>>
>>>> Now I found out what is going on here:
>>>>
>>>> In itd_urb_transaction() we allocate 9 iTDs for each URB with
>>>> number_of_packets == 64 in my case. The iTDs are added to
>>>> sched->td_list. For a frame-aligned scheduling we need 8 iTDs, the 9th
>>>> one is released back to the front of the streams free_list in
>>>> iso_sched_free(). This iTD was cleared after allocation and has a frame
>>>> number of 0 now. So for each allocation when now_frame == 0 we allocate
>>>> from the dma_pool, not from the free_list.
>>>
>>> Okay, that is a problem.  But it shouldn't be such a big problem,
>>> because now_frame should not be equal to 0 very often.
>>
>> Oh, wait, now I get it.  We never reach a steady state, because the
>> free list never shrinks, but occasionally it does increase when
>> now_frame is equal to 0.  Even though that doesn't happen very often,
>> the effects add up.
>>
>> Very good; tomorrow I will send your patch in.
>
> Hi Alan, Soeren
>
> Could you word the description a bit better. If Alan did not get it
> without a bit of thought, few others are going to understand it
> without a better explanation.
>
> Thanks
> 	Andrew
>

Alan,

can you come up with a better explanation, please? I think your 
description how it is supposed to work from here
    http://marc.info/?l=linux-usb&m=136345559432055&w=2
is required to understand the problem and the fix.

Thanks,
   Soeren
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