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

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Message-ID: <20130321173324.GY13280@titan.lakedaemon.net>
Date:	Thu, 21 Mar 2013 13:33:24 -0400
From:	Jason Cooper <jason@...edaemon.net>
To:	Soeren Moch <smoch@....de>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Arnd Bergmann <arnd@...db.de>,
	USB list <linux-usb@...r.kernel.org>,
	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 06:04:59PM +0100, Soeren Moch wrote:
> On 03/17/13 18:36, Alan Stern wrote:
> >On Sun, 17 Mar 2013, Soeren Moch wrote:
> >
> >>For each device only one isochronous endpoint is used (EP IN4, 1x 940
> >>Bytes, Interval 1).
> >>When the ENOMEM error occurs, a huge number of iTDs is in the free_list
> >>of one stream. This number is much higher than the 2*M entries, which
> >>should be there according to your description.
> >
> >Okay, but how did they get there?  With each URB requiring 9 iTDs, and
> >about 5 URBs active at any time, there should be about 5*9 = 45 iTDs in
> >use and 2*9 = 18 iTDs on the free list.  By the time each URB
> >completes, it should have released all 9 iTDs back to the free list,
> >and each time an URB is submitted, it should be able to acquire all 9
> >of the iTDs that it needs from the free list -- it shouldn't have to
> >allocate any from the DMA pool.
> >
> >Looks like you'll have to investigate what's going on inside
> >itd_urb_transaction().  Print out some useful information whenever the
> >size of stream->free_list is above 50, such as the value of num_itds,
> >how many of the loop iterations could get an iTD from the free list,
> >and the value of itd->frame in the case where the "goto alloc_itd"
> >statement is followed.
> >
> >It might be a good idea also to print out the size of the free list in
> >itd_complete(), where it calls ehci_urb_done(), and include the value
> >of ehci->now_frame.
> >
> 
> 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. 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.
> 
> Signed-off-by: Soeren Moch <smoch@....de>

Wow!  Great work Soeren!  Talk about a long road to a small fix.  Thanks
for keeping after it.

thx,

Jason.

> 
> 
> 

> --- linux-3.9.0-rc3-guru/drivers/usb/host/ehci-sched.c.orig	2013-03-21 17:36:21.000000000 +0100
> +++ linux-3.9.0-rc3-guru/drivers/usb/host/ehci-sched.c	2013-03-21 17:38:56.000000000 +0100
> @@ -1214,6 +1214,7 @@ itd_urb_transaction (
>  
>  		memset (itd, 0, sizeof *itd);
>  		itd->itd_dma = itd_dma;
> +		itd->frame = -1;
>  		list_add (&itd->itd_list, &sched->td_list);
>  	}
>  	spin_unlock_irqrestore (&ehci->lock, flags);
> @@ -1915,6 +1916,7 @@ sitd_urb_transaction (
>  
>  		memset (sitd, 0, sizeof *sitd);
>  		sitd->sitd_dma = sitd_dma;
> +		sitd->frame = -1;
>  		list_add (&sitd->sitd_list, &iso_sched->td_list);
>  	}
>  

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