o Don't call vm_willexit() more than once upon normal process exit
o Correct two cases of indenting of the no-discussion-possible kind
o Perform slightly stricter ptrace(2) checks:
- process calling ptrace must be target process's parent
- process must call wait/waitpid before using ptrace on stopped child
- no ptrace on zombies
o Allow user processes to use ptrace(T_STOP) to stop an active child
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