allocated in a fork(2)-inheritable way at the beginning or end of an
accept(2) system call. This test creates a test thread and blocks it
in accept(2), then forks a child process which tests to see if the
next available file descriptor is defined or not (EBADF vs EINVAL for
ftruncate(2)).
This detects a regression introduced during the network stack locking
work, in which a very narrow race during which fork(2) from one
thread during accept(2) in a second thread lead to an extra inherited
file descriptor turned into a very wide race ensuring that a
descriptor was leaked into the child even though it hadn't been
returned.
PR: kern/130348
d0e723a10c