Re: [Lse-tech] [PATCH 09/11] Task watchers: Add support for per-task watchers

Matt Helsley
2006-06-21T02:37:50Z

On Tue, 2006-06-20 at 18:46 -0700, Andrew Morton wrote:
> On Tue, 20 Jun 2006 18:20:48 -0700
> Matt Helsley <matthltc@us.ibm.com> wrote:
>
> > > > > > +static inline int notify_per_task_watchers(unsigned int val,
> > > > > > + struct task_struct *task)
> > > > > > +{
> > > > > > + if (get_watch_event(val) != WATCH_TASK_INIT)
> > > > > > + return raw_notifier_call_chain(&task->notify, val, task);
> > > > > > + RAW_INIT_NOTIFIER_HEAD(&task->notify);
> > > > > > + if (task->real_parent)
> > > > > > + return raw_notifier_call_chain(&task->real_parent->notify,
> > > > > > + val, task);
> > > > > > +}
> > > > >
> > > > > It's possible for this task to exit without returning a result.
> > > >
> > > > Assuming you meant s/task/function/:
> > > >
> > > > In the common case this will return a result because most tasks have a
> > > > real parent. The only exception should be the init task. However, the
> > > > init task does not "fork" from another task so this function will never
> > > > get called with WATCH_TASK_INIT and the init task.
> > > >
> > > > This means that if one wants to use per-task watchers to associate data
> > > > and a function call with *every* task, special care will need to be
> > > > taken to register with the init task.
> > >
> > > no......
> >
> > I've been looking through the source and, from what I can see, the end
> > of the function is not reachable. I think I need to add:
> >
> > notify_watchers(WATCH_TASK_INIT, &init_task);
> >
> > to make this into an applicable warning.
>
> If the end of the function isn't reachable then the
> `if (task->real_parent)' can simply be removed.

You're right -- good point.

Cheers,
-Matt Helsley