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

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Message-ID: <Pine.LNX.4.44L0.0805211040160.2490-100000@iolanthe.rowland.org>
Date:	Wed, 21 May 2008 10:42:02 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	David Vrabel <david.vrabel@....com>
cc:	Oliver Neukum <oliver@...kum.org>, Jiri Kosina <jkosina@...e.cz>,
	Greg KH <greg@...ah.com>, <linux-usb@...r.kernel.org>,
	<lchiquitto@...ell.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] USB: fix deadlock in HCD code

On Wed, 21 May 2008, David Vrabel wrote:

> Alan Stern wrote:
> > 
> > The functions you are worried about (usb_hcd_link_urb_to_ep and 
> > usb_hcd_unlink_urb_from_ep) are documented as requiring that interrupts 
> > be disabled by their callers.  This patch isn't needed.
> 
> This requirement is the only reason the whci-hcd driver disables
> interrupts.  Removing this requirement would reduce the time that
> interrupts are disabled in the whci-hcd driver.

That doesn't sound like a valid approach.  If you don't disable
interrupts then you aren't protected against an interrupt handler
submitting an URB and accessing your data structures while whci-hcd is
in the middle of updating them.

Alan Stern

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