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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