Re: [PATCH 1/1] khubd -- switch USB product/manufacturer/serialhandling to RCU

From: Greg KH
Date: Mon Jun 14 2010 - 12:29:41 EST

On Mon, Jun 14, 2010 at 12:15:41PM +0100, Andy Whitcroft wrote:
> With the introduction of wireless USB hubs the product, manufacturer,
> and serial number are now mutable.

Changable by whom? The device itself? This has always been the case,
although it is usually very rare for a device to do this.

> This necessitates new locking in the gconsumers of these values
> including the sysfs read routines in order to prevent use-after-free
> acces to these values.

Who would access them after they go away?

> These extra locks create significant lock contention leading to
> increased boot times (0.3s for an example Atom based system).

Who is doing all of the deauthorization at boot time that this would
ever matter at all?

> Move update of these values to RCU based locking.

Ick. What has changed that necessitates this? You discuss a variety of
different things in this bug report:

> BugLink:

Which would have been nice to dicuss with the people on these lists. I
really don't think this is the correct fix, as a normal boot path
shouldn't be having non-authorized usb devices, right? And from that
bug, once the machine is up and running, there is no contention here,

not convinced,

greg k-h
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