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port_create race test and fix #215

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port_create race test and fix #215

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Commits on Dec 22, 2017

  1. app/tests/port_tests.c: add two_threads_race test 

    This change adds a test to the port_tests suite
to trigger the port_create() race.  When tested with
an SMP (3) qemu instance, the race is discovered in
less than twenty iterations and often much sooner.
    @redpig
    redpig committed Dec 22, 2017
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  2. kernel/port.c: protect against port_create() race 

    In the current design, ports may be created with the same name
because of time-of-check-time-of-use behavior.

This change adds a new port magic, PORTHOLD_MAGIC, which cannot be
accessed using the normal accessors. It is injected into the list
upon a successful, locked search for a name.  It holds the name
until the allocation happens. At which point the port-hold is
deleted and the real port is added while, again, under the thread
lock.

This change assumes using a stack-allocated port is desirable over
preallocating and freeing on each port_create().  If the overhead
of allocation is low, then pre-allocating the new port would be
the cleanest option: (1) allocate, (2) check for collisions,
(3) add to list.

This fix is confirmed by the two_threads_race test completing its
256 iterations without a race. It also fixes the test to expect
ERR_BUSY and to exit cleanly, as it had never completed before.
    @redpig
    redpig committed Dec 22, 2017
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  3. app/tests/port_tests.c: fix bad indents

    @redpig
    redpig committed Dec 22, 2017
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  4. app/tests/port_tests.c: static-ify consts 

    This change makes the shared constants static
as well as const-ifies shared packets.
    @redpig
    redpig committed Dec 22, 2017
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