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    SubjectRe: [PATCH 9/9] ptrace: Don't change __state
    On 04/26, Eric W. Biederman wrote:
    >
    > static void ptrace_unfreeze_traced(struct task_struct *task)
    > {
    > - if (READ_ONCE(task->__state) != __TASK_TRACED)
    > + if (!(READ_ONCE(task->jobctl) & JOBCTL_DELAY_WAKEKILL))
    > return;
    >
    > WARN_ON(!task->ptrace || task->parent != current);
    > @@ -213,11 +213,10 @@ static void ptrace_unfreeze_traced(struct task_struct *task)
    > * Recheck state under the lock to close this race.
    > */
    > spin_lock_irq(&task->sighand->siglock);

    Now that we do not check __state = __TASK_TRACED, we need lock_task_sighand().
    The tracee can be already woken up by ptrace_resume(), but it is possible that
    it didn't clear DELAY_WAKEKILL yet.

    Now, before we take ->siglock, the tracee can exit and another thread can do
    wait() and reap this task.

    Also, I think the comment above should be updated. I agree, it makes sense to
    re-check JOBCTL_DELAY_WAKEKILL under siglock just for clarity, but we no longer
    need to do this to close the race; jobctl &= ~JOBCTL_DELAY_WAKEKILL and
    wake_up_state() are safe even if JOBCTL_DELAY_WAKEKILL was already cleared.

    > @@ -2307,6 +2307,7 @@ static int ptrace_stop(int exit_code, int why, int clear_code,
    >
    > /* LISTENING can be set only during STOP traps, clear it */
    > current->jobctl &= ~JOBCTL_LISTENING;
    > + current->jobctl &= ~JOBCTL_DELAY_WAKEKILL;

    minor, but

    current->jobctl &= ~(JOBCTL_LISTENING | JOBCTL_DELAY_WAKEKILL);

    looks better.

    Oleg.

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