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

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Message-ID: <20130321212033.GQ21478@lunn.ch>
Date:	Thu, 21 Mar 2013 22:20:33 +0100
From:	Andrew Lunn <andrew@...n.ch>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Soeren Moch <smoch@....de>, Arnd Bergmann <arnd@...db.de>,
	USB list <linux-usb@...r.kernel.org>,
	Jason Cooper <jason@...edaemon.net>,
	Andrew Lunn <andrew@...n.ch>,
	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 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
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