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[Tim Gardner <tim.gardner@xxxxxxxxxxxxx>]

8d91f8b15361dfb438ab6eb3b319e2ded43458ff ('printk: do cond_resched()
between lines while outputting to consoles') came in via 4.4 stable. I
also cherry-picked 6b97a20d3a7909daa06625d4440c2c52d7bf08d7 ('printk:
set may_schedule for some of console_trylock() callers')

** Also affects: linux (Ubuntu Xenial)
   Importance: Medium
     Assignee: Dan Streetman (ddstreet)
       Status: In Progress

** Changed in: linux (Ubuntu Xenial)
       Status: In Progress => Fix Committed

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https://bugs.launchpad.net/bugs/1534216

Title:
  lots of printk to serial console can hang system for long time

Status in linux package in Ubuntu:
  Fix Committed
Status in linux source package in Xenial:
  Fix Committed

Bug description:
  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.

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