| Date | Wed, 27 Apr 2022 17:41:59 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 9/9] ptrace: Don't change __state |
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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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