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73416ba
(Get the code!)
After checking the log and the code, in fact there isn't a deadlock, just a big wait while holding tty lock.
There is a problem with the GSM modem. In the log we can see it keeps connecting and disconnecting from usb. Eventually, the modem stops to answer, and usb_control_msg called by option driver starts to timeout probably. The timeout is somewhat big (5s), and this timeout occurs while we have the "big tty lock" held, so everything which tries to access any tty related ends up waiting ~5 seconds until the function timeouts and returns to tty layer which releases the lock.
So the real issue is with the 3g modem. I see in the log some related failures to usb_modeswitch, perhaps it's confusing the modem sending a bad command, which leaves it in a bad state, making it disconnecting and reconnecting, and it stops to answer to usb_control_msg properly.