Okay, I found the cause of the hang.  It is a simple bug in the USB
scatter-gather library, caused by changes added in response to the S-G
chaining modification.

This patch (as1125) fixes a bug in the USB scatter-gather library.
Early exit from the S-G initialization loop does not reset the count of
outstanding URBs.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Cc: Matthew Dharm <mdharm-usb@one-eyed-alien.net>
Cc: David Brownell <david-b@pacbell.net>
Cc: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>