From: Peter W. <pwi...@bi...> - 2006-06-21 13:23:18
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Peter Williams wrote: > Peter Williams wrote: >> Andrew Morton wrote: >>> On Tue, 20 Jun 2006 18:20:48 -0700 >>> Matt Helsley <mat...@us...> 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 pwi...@bi... "Learning, n. The kind of ignorance distinguishing the studious." -- Ambrose Bierce |