Cornelia Huck wrote:
> On Wed, 18 Apr 2007 03:41:10 +0900,
> Tejun Heo <[email protected]> wrote:
>
>> Hello, all.
>>
>> Agreed with the problem but I'm not very enthusiastic for adding
>> kobj->owner. How about the following? exit() routines will have to
>> do device_unregister_wait() instead of device_unregister(). On return
>> from it, it's guaranteed that all references to it are dropped and
>> ->release is finished.
>
> Sounds interesting. Kind of like the completion approach, but with the
> dangerous bits outside the module.
>
>> The caller is responsible for avoiding
>> deadlock, of course.
>
> I think that wording is a bit too strong. Of course, if the device is
> unregistered in the exit routine, the module must make sure it gave up
> all references it itself obtained. However, it doesn't have any control
> about who obtained a reference during the object's lifetime. If an
> outsider holds on to a reference, we'll lock up until this reference
> has been given up (but I guess this is what we want).
Right, the better wording would be "the caller is responsible for not
causing deadlocks by dropping all references it owns on entry".
>> +void kobject_put_wait(struct kobject * kobj)
>> +{
>> + struct kobj_wait kwait;
>> + unsigned long flags;
>> +
>> + if (!kobj)
>> + return;
>> +
>> + BUG_ON(!list_empty(&kobj->entry));
>> +
>> + init_completion(&kwait.cmpl);
>> + kwait.kobj = kobj;
>> +
>> + spin_lock_irqsave(&kobj_wait_lock, flags);
>> + list_add(&kwait.list, &kobj_wait_list);
>> + spin_unlock_irqrestore(&kobj_wait_lock, flags);
>> +
>> + kobject_put(kobj);
>> +
>> + if (!wait_for_completion_timeout(&kwait.cmpl, 30 * HZ)) {
>> + printk(KERN_WARNING "kobject_put_wait: kobject %p is still "
>> + "alive after 30s, possible reference count bug\n", kobj);
>> + dump_stack();
>> + wait_for_completion(&kwait.cmpl);
>> + }
>> +}
>>
>
> Couldn't this waiting be made simpler?
> - add completion to kobject in kobject_unregister_wait()
> - call kobject_put(), then wait_for_completion()
> - in kobject_cleanup(), save completion from kobject, call release
> function, then complete() on saved completion
I was trying to avoid adding a completion to all kobjects.
Thanks.
--
tejun
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