[PATCH 0/5] ptrace-utrace: fix exit_ptrace() vs ptrace_report_signal() races

[Oleg Nesterov]

In short: exit_ptrace()->ptrace_detach_task() is very wrong when it
tries to detach the !stopped tracee, we can not trust get_stop_event()
in this case.

This means that in the case like

        ptrace(PTRACE_CONT, ..., SIGXXX);
        exit(); // ---> calls ptrace_detach_task()

the tracee can miss SIGXXX if ptrace_detach_task() does
utrace_control(UTRACE_DETACH) before the tracee calls ->report_signal().

5/5 is the actual fix. 1-4 are preparations to simplify the review
and document the changes.

Oleg.