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

From: Soeren Moch
Date: Thu Mar 21 2013 - 18:16:27 EST

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.



can you come up with a better explanation, please? I think your description how it is supposed to work from here
is required to understand the problem and the fix.

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