Re: [PATCH] ptrace: fix ptrace_unfreeze_traced() race with rt-lock

[Oleg Nesterov <oleg@redhat.com>]

On 11/02, Sebastian Andrzej Siewior wrote:
>
> On 2020-11-02 17:25:14 [+0100], Oleg Nesterov wrote:
> > On 11/02, Oleg Nesterov wrote:
> > >
> > >  	spin_lock_irq(&task->sighand->siglock);
> > > -	if (task->state == __TASK_TRACED) {
> > > -		if (__fatal_signal_pending(task))
> > > -			wake_up_state(task, __TASK_TRACED);
> > > -		else
> > > -			task->state = TASK_TRACED;
> > > -	}
> > > +
> > > +	raw_spin_lock(&task->pi_lock);
> >
> > but perhaps it should be raw_spin_lock_irq() ?
> >
> > I know nothing about kernel-rt, however it seems that spin_lock_irq()
> > from include/linux/spinlock_rt.h doesn't disable irqs?
>
> I don't exactly how much breaks when we turn siglock into a
> raw_spinlock_t but there is a memory allocation in __send_signal() which
> is a no no.
>
> There is task_is_traced() which looks under the PI lock for the task
> state to be sure (we a few of those). I haven't looked at the patch yet…

So it seems I should send V2 which uses raw_spin_(un)lock_irq().

Or even _irqsave() like ptrace_freeze_traced() does? Although this looks
confusing, exactly because ptrace_freeze_traced() calls task_is_traced()
which does raw_spin_lock_irq().

Oleg.