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

[Peter Williams <pwil3058@bigpond.net.au>]

Peter Williams wrote:
> 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.
> 
> 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.

Peter
-- 
Peter Williams                                   pwil3058@bigpond.net.au

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