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    SubjectRe: [PATCH 10/10] ptrace: implement group stop notification for ptracer
    On 05/16, Tejun Heo wrote:
    > When group stop state of a seized tracee changes, JOBCTL_TRAP_NOTIFY
    > is set, which triggers STOP trap but is sticky until the next

    I simply can't understand this patch. And the supposed API as it seen
    by the user-space. I'll try to read it again and think more.

    A couple of questions,

    > +static void ptrace_trap_notify(struct task_struct *t)
    > +{
    > + siginfo_t *si = t->last_siginfo;
    > +
    > + WARN_ON_ONCE(!(t->ptrace & PT_SEIZED));
    > + assert_spin_locked(&t->sighand->siglock);
    > +
    > + /*
    > + * @t is being ptraced and new SEIZE behavior is in effect.
    > + * Schedule sticky trap which will clear on the next GETSIGINFO.
    > + */
    > + t->jobctl |= JOBCTL_TRAP_NOTIFY;

    This is also set by do_signal_stop(). Cleared by PTRACE_GETSIGINFO.

    How can this work? Doesn't this mean PTRACE_GETSIGINFO becomes mandatory
    before PTRACE_CONT? IOW, unless the tracee does PTRACE_GETSIGINFO to clear
    this bit, PTRACE_CONT just leads to another trap, no?

    > + if (task_is_traced(t) && si && si->si_code == PTRACE_STOP_SI_CODE) {

    OK, this PTRACE_STOP_SI_CODE check is clear. But the same check in
    ptrace_check_attach() looks confusing, why can't we set BLOCK_NOTIFY

    > + t->jobctl |= JOBCTL_TRAPPING;
    > + if (!(t->jobctl & JOBCTL_BLOCK_NOTIFY))
    > + signal_wake_up(t, true);

    Could you please remind me why we can't avoid the awful ptrace_wait_trapping()
    in do_wait() paths? Assuming that ptrace_check_attach() does this. I got lost
    a bit.

    So. The tracee reports PTRACE_EVENT_STOP, debugger issues a lot of PTRACE_
    requests. The tracee can report another trap "in between". Looks confusing...
    Perhaps I need to get used to it.


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