linux-kernel - Re: [PATCH] usb ehci_iaa

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Message-ID: <Pine.LNX.4.44L0.0804021658170.2107-100000@iolanthe.rowland.org>
Date:	Wed, 2 Apr 2008 17:08:59 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	David Brownell <david-b@...bell.net>
cc:	Mark Lord <lkml@....ca>, <pavel@...e.cz>, <oliver@...kum.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<jikos@...e.cz>, <gregkh@...e.de>, <akpm@...ux-foundation.org>
Subject: Re: [PATCH] usb ehci_iaa_watchdog fix

On Wed, 2 Apr 2008, David Brownell wrote:

> > It fixes the cause rather than the symptom.
> 
> I'm not sure I'd agree with that.

Really?  The logic seemed clear enough to me.

     1. Evidently the ehci_iaa_watchdog routine was getting called at a 
	time when the host controller wasn't running -- which had to
	have been after it was suspended.

     2. But ehci_bus_suspend() calls end_unlink_async(), which turns
	off the IAA watchdog timer.

     3. Hence the timer must have been restarted later on while 
	ehci_bus_suspend() was still running.  The call to ehci_work() 
	appeared to be the only place that could have happened.

     4. Thus moving the end_unlink_async() call to after ehci_work()
	(or just to be doubly safe, after ehci_halt() and the change
	to HC_STATE_SUSPENDED) should take care of all pending QH
	unlinks and leave none of them unfinished.

Strictly speaking, it would be best to move the del_timer_sync() calls
to after ehci_lock is released.  But it doesn't really matter if the
timer routines get invoked after the controller is suspended.

Alan Stern

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