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SubjectRe: [PATCH 6/9] signal: Always call do_notify_parent_cldstop with siglock held
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...

Oleg.

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