In fork_init a division by zero may occur.

In the first patch the calculation of max_threads is moved from fork_init
to a new separate function.

The incorrect calculation of max threads is addressed in the 
second patch.

Furthermore max_threads is checked against FUTEX_TID_MASK.

The third patch addresses max_threads being set by writing to
/proc/sys/kernel/threads-max. The same limits are applied as
in fork_init. 

New in version 5:
  Do not update limits of the init process
  Do not update max_threads on memory hotplug events
  Corrections to commit messages

New in version 4:
  Separation of refactoring and correction into separate patches
  (as requested by Ingo Molnar)
  Remove redundant argument of fork_init

New in version 3:
  Determination of max_threads moved to separate function.
  Handling of /proc/sys/kernel/threads-max
  Handling of memory hotplugging.

New in version 2:
  Use div64_u64 for 64-bit division.

Thank you for your helpful feedback:
  Andrew Morton <a...@linux-foundation.org>
  Guenter Roeck <li...@roeck-us.net>
  Ingo Molnar <mi...@kernel.org>
  Oleg Nesterov <o...@redhat.com>
  Peter Zijlstra <pet...@infradead.org>
  Vladimir Davydov <vdavy...@parallels.com>
 

Heinrich Schuchardt (3):
  kernel/fork.c: new function for max_threads
  kernel/fork.c: avoid division by zero
  kernel/sysctl.c: threads-max observe limits

 include/linux/sysctl.h |  3 ++
 init/main.c            |  4 +--
 kernel/fork.c          | 75 +++++++++++++++++++++++++++++++++++++++++---------
 kernel/sysctl.c        |  6 ++--
 4 files changed, 69 insertions(+), 19 deletions(-)

-- 
2.1.4

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