kern/52634: possible unhandled spurious wakeup in posix_spawn

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

>Number:         52634
>Category:       kern
>Synopsis:       possible unhandled spurious wakeup in posix_spawn
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Oct 20 16:00:00 +0000 2017
>Originator:     Taylor R Campbell <riastradh%NetBSD.org@localhost>
>Release:        NetBSD-current
>Organization:
The NetBSD Foundation
>Environment:
any
>Description:

	do_posix_spawn calls cv_wait without looping on a test for a
	condition, which may cause it to return before the child is
	ready -- and potentially even to read and return an
	uninitialized error -- in the case of a spurious wakeup:

	https://nxr.netbsd.org/xref/src/sys/kern/kern_exec.c?r=1.448#2605

>How-To-Repeat:

	Code inspection.

>Fix:

	Yes, please!