Re: [PATCH] USB: EHCI: fix for leaking isochronous data
From: Andrew Lunn
Date: Thu Mar 21 2013 - 17:20:53 EST
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.
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