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    SubjectRe: [PATCH 03/10] ptrace: implement PTRACE_SEIZE
    Hello,

    On Wed, May 18, 2011 at 08:17:56PM +0200, Oleg Nesterov wrote:
    > On 05/16, Tejun Heo wrote:
    > >
    > > @@ -315,6 +338,9 @@ static int ptrace_attach(struct task_struct *task)
    > > if (task_is_stopped(task)) {
    > > task->jobctl |= JOBCTL_TRAP_STOP | JOBCTL_TRAPPING;
    > > signal_wake_up(task, 1);
    > > + } else if (seize) {
    > > + task->jobctl |= JOBCTL_TRAP_STOP;
    >
    > So, this can race with do_signal_stop(), it can clear TRAP_STOP and
    > JOBCTL_STOP_PENDING can guarantee the tracee will trap later.

    Confused. How can do_signal_stop() clear TRAP_STOP?

    > > + * When PT_SEIZED, it's used for both group stop and explicit
    > > + * SEIZE/INTERRUPT traps. Both generate PTRACE_EVENT_STOP trap
    > > + * with accompanying siginfo.
    > > + *
    > > + * When !PT_SEIZED, it's used only for group stop trap with
    > > + * CLD_STOPPED as exit_code and no siginfo.
    > > */
    > > if (unlikely(current->jobctl & JOBCTL_TRAP_MASK)) {
    > > - signr = current->jobctl & JOBCTL_STOP_SIGMASK;
    > > - WARN_ON_ONCE(!signr);
    > > - ptrace_stop(signr, CLD_STOPPED, 0, NULL);
    > > - current->exit_code = 0;
    > > + if (current->ptrace & PT_SEIZED) {
    > > + ptrace_do_notify(SIGTRAP | PTRACE_EVENT_STOP << 8,
    > > + CLD_STOPPED);
    >
    > So. When PT_SEIZED, we always report PTRACE_EVENT_STOP and PTRACE_GET_SIGINFO
    > always works.
    >
    > Personally I agree, this looks more clean and natural.

    Yeah, I like it much better. INTERRUPT trap and group stop trap being
    separate while sharing some attributes was disturbing.

    Thanks.

    --
    tejun


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