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SubjectRe: [PATCH 7/8] job control: Notify the real parent of job control events regardless of ptrace
On Mon, Mar 21, 2011 at 06:43:06PM +0100, Oleg Nesterov wrote:
> > + * Test whether the target task of the usual cldstop notification - the
> > + * real_parent of the group_leader of @child - is the ptracer.
> > + */
> > +static bool real_parent_is_ptracer(struct task_struct *child)
> > +{
> > + return child->parent == child->group_leader->real_parent;
> > +}
>
> Again, I am not sure we do not need same_thread_group(), but this
> is minor.

Yeah, same_thread_group() would be better.

> Hmm... in fact I can't convince myself we really need to look at
> child->group_leader, will recheck... Anyway, this is minor too.

Care to elaborate?

> > @@ -1757,7 +1768,20 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
> > spin_unlock_irq(&current->sighand->siglock);
> > read_lock(&tasklist_lock);
> > if (may_ptrace_stop()) {
> > - do_notify_parent_cldstop(current, task_ptrace(current), why);
> > + /*
> > + * 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 && !real_parent_is_ptracer(current))
> > + do_notify_parent_cldstop(current, false, why);
>
> OK.
>
> But what about "else" branch? If gstop_done == T but debugger has gone
> between spin_unlock(siglock) and read_lock(tasklist), we should do
> something.
>
> ptrace_untrace() restores GROUP_STOP_PENDING in this case, so this task
> will stop again. But notification is lost.
>
> Just in case, it is not that I blame this patch. Just I think we need
> a bit more changes here. Unless I missed something.

You mean when may_ptrace_stop() fails, right? Yeah, we need
notification in the else clause. Will add it.

Thanks.

--
tejun


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