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

Peter Williams
2006-06-21T01:55:56Z

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?

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

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