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SubjectRe: [PATCH v2 1/5] sched,signal,ptrace: Rework TASK_TRACED, TASK_STOPPED state
On Tue, Apr 26, 2022 at 06:34:09PM -0500, Eric W. Biederman wrote:
> Peter Zijlstra <peterz@infradead.org> writes:
>
> > Currently ptrace_stop() / do_signal_stop() rely on the special states
> > TASK_TRACED and TASK_STOPPED resp. to keep unique state. That is, this
> > state exists only in task->__state and nowhere else.
> >
> > There's two spots of bother with this:
> >
> > - PREEMPT_RT has task->saved_state which complicates matters,
> > meaning task_is_{traced,stopped}() needs to check an additional
> > variable.
> >
> > - An alternative freezer implementation that itself relies on a
> > special TASK state would loose TASK_TRACED/TASK_STOPPED and will
> > result in misbehaviour.
> >
> > As such, add additional state to task->jobctl to track this state
> > outside of task->__state.
> >
> > NOTE: this doesn't actually fix anything yet, just adds extra state.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>
> > --- a/kernel/signal.c
> > +++ b/kernel/signal.c
> > @@ -770,7 +773,9 @@ void signal_wake_up_state(struct task_st
> > * By using wake_up_state, we ensure the process will wake up and
> > * handle its death signal.
> > */
> > - if (!wake_up_state(t, state | TASK_INTERRUPTIBLE))
> > + if (wake_up_state(t, state | TASK_INTERRUPTIBLE))
> > + t->jobctl &= ~(JOBCTL_STOPPED | JOBCTL_TRACED);
> > + else
> > kick_process(t);
> > }
>
> This hunk is subtle and I don't think it is actually what we want if the
> code is going to be robust against tsk->__state becoming TASK_FROZEN.

Oooh, indeed. Yes, let me go back to that resume based thing as you
suggest.

But first, let me go read all your patches :-)

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