Re: OHCI hangs after failing to free resources

On Fri, 4 May 2007, Mike Nuss wrote:

> Further support (I dumped the 'dummy' td before freeing it). This is a
> new trace so the addresses won't match the last trace.
> 
> kernel: ohci_hcd 0000:00:13.0: leak ed c3e8e680 (#82) state 0 (has tds)
> kernel: ohci_hcd 0000:00:13.0: ed->dummy td c3e8d8c0; urb 00000000 index
> 0; hw next td 03e8d8c0
> ohci_hcd 0000:00:13.0:      info 00000000 CC=0 (CARRY) DI=0 SETUP 
> ohci_hcd 0000:00:13.0:      cbp 00000000 be 00000000 (len 0)
> ohci_hcd 0000:00:13.0: free ed->dummy: td c3e8d8c0
> 
> ed->dummy has a non-null next pointer! I don't believe that should ever
> be the case.

No, that's normal.  Read ohci-mem.c:td_alloc() and you'll see that each 
newly-allocated TD has its hwNextTD field set to point at itself.

In your previous messages you found that the

		/* INTR_WDH may need to clean up first */
		if (td->td_dma != head)
			goto skip_ed;

path was followed.  This indicates that a WDH signal isn't being received; 
the driver isn't getting a notification from the controller that the TD 
stored at 0x3e3d400 has been completed.  In fact, maybe the controller 
isn't completing that TD at all -- it doesn't appear to be on the done 
list.  But the HeadP pointer gets advanced beyond it.

As I understand it, the controller is always supposed to advance the HeadP 
pointer at the same time as it moves a TD to the done list, and it's 
supposed to generate an IRQ when the done list's head is changed.

Can you get a complete dump of all the ED and TD structures when the error 
occurs?  There's code in ohci-dbg.c to do it for you.

Alan Stern


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