On Thu, Aug 14, 2003 at 01:21:22PM -0700, David Brownell wrote:
Alan Stern wrote:
I foresee races between set_bConfigurationValue() and disconnect. But that's not something I can fix in two minutes.
Could you elaborate? I don't think I added any new races there.
Maybe not, but perhaps you exacerbated an existing race. I'm not sure; I haven't examined the code interactions in detail.
This is a problem generic to sysfs attribute files: They can persist and be writeable long after you want them to go away. If a user process has an attribute file open, then calling device_remove_file() won't prevent the show() and store() routines from being invoked. (I have a patch for sysfs that would prevent that, but nobody seems interested in it.) If someone tries to write the config value for a usb_device after it has disconnected and much of its state has gone away, what will happen?
Part of that is a sysfs question...
Both usb_set_configuration() and usb_disconnect() are going to want to call usb_disable_device() to shut down all pending operations before they do the next step.
And that will fail if the device is not really there, right?
No, it'll succeed -- it _must_ scrub out all pending requests and the HCD state for all previously-active device endpoints. But if the device is already NOTATTACHED, then usb_set_configuration() won't try that and the SET_CONFIGURATION request will fail cleanly.
So the specific case Alan asked about is ok except for a small window caused by usb_disconnect() not synchronizing with anything, so that _concurrent_ calls to that and to usb_set_configuration() may hit latent bugs. I'd rather patch those later.
- Dave
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