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

From: Alan Stern
Date: Thu Mar 21 2013 - 17:06:59 EST

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.

> The attached patch
> invalidates the frame number in each iTD before it is sent to the
> scheduler. This fixes the problem without the need to iterate over a iTD
> list.

The patch looks okay. However I would like to understand why the 0
frame value messes things up so much.

Alan Stern

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