linux-kernel - Re: [PATCH] USB: fix deadlock in HCD code

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Message-Id: <48344E8A.7E42.0086.0@novell.com>
Date:	Wed, 21 May 2008 13:32:10 -0600
From:	"Leonardo Chiquitto" <lchiquitto@...ell.com>
To:	"Alan Stern" <stern@...land.harvard.edu>,
	"Jiri Kosina" <jkosina@...e.cz>
Cc:	"Greg KH" <greg@...ah.com>, "Oliver Neukum" <oliver@...kum.org>,
	<linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>
Subject: Re: [PATCH] USB: fix deadlock in HCD code


>> > > Used in the suspend code. Your patch is indeed correct, but I fear 
>> > > there might be a second bug caused by wrong calling conditions.
>> > The problem in the Novell bugzilla entry was caused by the fact that the 
>> > OHCI irq routine was invoked with interrupts enabled, owing to a missing 
>> > IRQF_DISABLED flag.  That bug has already been fixed in 2.6.25.
>> 
>> That indeed is 2.6.25 kernel. I guess you are talking about commit 
>> 442258e2ff69 here.
> 
> Yes.
> 
>> If so, the reporter is definitely using the kernel 
>> containing this commit, and the lockups still trigger.
>> 
>> Seems that my patch is papering over the real bug (someone enabling 
>> interrupts somewhere) indeed, but I can't seem to be able to find such 
>> codepath.
> 
> You could try testing the interrupt-enable flag at various places 
> in ohci-hcd (start with finish_urb) and printing an error message if 
> interrupts are enabled.
> 
> One possibility is that in an earlier call to finish_urb,
> usb_hcd_giveback_urb was called with interrupts disabled and returned 
> with interrupts enabled.  In other words, some driver's callback 
> routine may have enabled interrupts incorrectly.

Alan,

  I am trying your suggestion right now. Lets see if it finds something.

Thanks,
Leonardo

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