Re: [PATCH v4 10/12] ptrace: Don't change __state

Oleg Nesterov
2022-05-10T15:34:53Z

On 05/10, Eric W. Biederman wrote:
>
> > But I still think that a lockless
> >
> > if (!(task->jobctl & JOBCTL_PTRACE_FROZEN))
> > return;
> >
> > check at the start of ptrace_unfreeze_traced() makes sense to avoid
> > lock_task_sighand() if possible.
> >
> > And ptrace_resume() can probably clear JOBCTL_PTRACE_FROZEN along with
> > JOBCTL_TRACED to make this optimization work better. The same for
> > ptrace_signal_wake_up().
>
> What do you have that suggests that taking siglock there is a problem?

Not necessarily a problem, but this optimization is free. If the tracee
was resumed, it can compete for siglock with debugger.

> What you propose will definitely work as an incremental change, and
> in an incremental change we can explain why doing the stupid simple
> thing is not good enough.

OK.

Oleg.