Public bug reported:

This is a clone from bug 1505564, to track the separate issue of the
serial port driver failing to schedule itself off its cpu.

The original bug's problem was caused by the kernel spamming a huge
number of error messages in a certain situation.  Normally, that would
not be a problem, but in this case the system is virtualized, and logs
over its serial port.  When the massive number of kernel messages are
sent to the serial port driver, it can't keep up, so sending all the log
messages can take a very long time - minutes or longer - and the serial
port driver fails to schedule itself off the cpu it's using during that
time.  That results in other cpus hanging, waiting for the serial port
driver's cpu to become avaiable.

I'll  update the bug with more details as I debug.

** Affects: linux (Ubuntu)
     Importance: Undecided
     Assignee: Dan Streetman (ddstreet)
         Status: In Progress

** Tags: sts

** Changed in: linux (Ubuntu)
     Assignee: (unassigned) => Dan Streetman (ddstreet)

** Changed in: linux (Ubuntu)
       Status: New => In Progress

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  serial port driver in some virtual systems can hang

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