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SubjectRe: [PATCH 6/9] signal: Always call do_notify_parent_cldstop with siglock held
On 04/27, Oleg Nesterov wrote:
>
> On 04/26, Eric W. Biederman wrote:
> >
> > @@ -2209,6 +2213,34 @@ static int ptrace_stop(int exit_code, int why, int clear_code,
> > spin_lock_irq(&current->sighand->siglock);
> > }
> >
> > + /* Don't stop if current is not ptraced */
> > + if (unlikely(!current->ptrace))
> > + return (clear_code) ? 0 : exit_code;
> > +
> > + /*
> > + * If @why is CLD_STOPPED, we're trapping to participate in a group
> > + * stop. Do the bookkeeping. Note that if SIGCONT was delievered
> > + * across siglock relocks since INTERRUPT was scheduled, PENDING
> > + * could be clear now. We act as if SIGCONT is received after
> > + * TASK_TRACED is entered - ignore it.
> > + */
> > + if (why == CLD_STOPPED && (current->jobctl & JOBCTL_STOP_PENDING))
> > + gstop_done = task_participate_group_stop(current);
> > +
> > + /*
> > + * Notify parents of the stop.
> > + *
> > + * While ptraced, there are two parents - the ptracer and
> > + * the real_parent of the group_leader. The ptracer should
> > + * know about every stop while the real parent is only
> > + * interested in the completion of group stop. The states
> > + * for the two don't interact with each other. Notify
> > + * separately unless they're gonna be duplicates.
> > + */
> > + do_notify_parent_cldstop(current, true, why);
> > + if (gstop_done && ptrace_reparented(current))
> > + do_notify_parent_cldstop(current, false, why);
>
> This doesn't look right too. The parent should be notified only after
> we set __state = TASK_TRACED and ->exit code.
>
> Suppose that debugger sleeps in do_wait(). do_notify_parent_cldstop()
> wakes it up, debugger calls wait_task_stopped() and then it will sleep
> again, task_stopped_code() returns 0.
>
> This can be probably fixed if you remove the lockless (fast path)
> task_stopped_code() check in wait_task_stopped(), but this is not
> nice performance-wise...

On the other hand, I don't understand why did you move the callsite
of do_notify_parent_cldstop() up... just don't do this?

Oleg.

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