Re: [PATCH] USB: fix deadlock in HCD code

From: David Vrabel
Date: Wed May 21 2008 - 10:54:42 EST

Alan Stern wrote:
> 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.

I can't see how urbs can be submitted to whci-hcd from an interrupt
handler (urb callbacks are always called from a workqueue thread) but
they could be submitted from a timer, so you are correct.

David Vrabel, Senior Software Engineer, Drivers
CSR, Churchill House, Cambridge Business Park, Tel: +44 (0)1223 692562
Cowley Road, Cambridge, CB4 0WZ
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