Date: Thu, 21 Mar 2013 17:06:54 -0400 (EDT)
From: Alan Stern <stern@rowland.harvard.edu>
To: Soeren Moch <smoch@web.de>
cc: Arnd Bergmann <arnd@arndb.de>, USB list <linux-usb@vger.kernel.org>,
        Jason Cooper <jason@lakedaemon.net>, Andrew Lunn <andrew@lunn.ch>,
        Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>,
        <linux-mm@kvack.org>,
        Kernel development list <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>, <michael@amarulasolutions.com>
Subject: Re: [PATCH] USB: EHCI: fix for leaking isochronous data
In-Reply-To: <514B3DBB.3060302@web.de>
Message-ID: <Pine.LNX.4.44L0.1303211659080.1899-100000@iolanthe.rowland.org>
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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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