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

[Peter Williams]

Peter Williams wrote:
> Peter Williams wrote:
> > Andrew Morton wrote:
> > > On Tue, 20 Jun 2006 18:20:48 -0700
> > > Matt Helsley <matthltc@xxxxxxxxxx> 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.
> >
> > Perhaps with a comment to say that it's safe (and why) to dereference 
> > task->real_parent to help code reviewers?
>
> Now that I understand this code better, I'm at a loss to understand why 
> you're calling the parent with the notifier.  I can't think of any 
> circumstances where this would be useful.

I spoke to soon and can now see how I can use this functionality.  If I 
register my per task watcher with init_task, this functionality will 
allow me to do away with the normal watcher.

Sorry for doubting,
Peter
--
Peter Williams                                   pwil3058@xxxxxxxxxxxxxx

"Learning, n. The kind of ignorance distinguishing the studious."
 -- Ambrose Bierce
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