Re: [PATCH v3 07/22] kthread: Detect when a kthread work is used by more workers

Hello, Petr.

On Tue, Nov 24, 2015 at 11:06:50AM +0100, Petr Mladek wrote:

quoted

quoted

@@ -610,6 +625,12 @@ repeat:
 	if (work) {
 		__set_current_state(TASK_RUNNING);
 		work->func(work);
+
+		spin_lock_irq(&worker->lock);
+		/* Allow to queue the work into another worker */
+		if (!kthread_work_pending(work))
+			work->worker = NULL;
+		spin_unlock_irq(&worker->lock);

Doesn't this mean that the work item can't be freed from its callback?
That pattern tends to happen regularly.

I am not sure if I understand your question. Do you mean switching
work->func during the life time of the struct kthread_work? This
should not be affected by the above code.

So, something like the following.

void my_work_fn(work)
{
	struct my_struct *s = container_of(work, ...);

	do something with s;
	kfree(s);
}

and the queuer does

	struct my_struct *s = kmalloc(sizeof(*s));

	init s and s->work;
	queue(&s->work);

expecting s to be freed on completion.  IOW, you can't expect the work
item to remain accessible once the work function starts executing.

The above code allows to queue an _unused_ kthread_work into any
kthread_worker. For example, it is needed for khugepaged,
see http://marc.info/?l=linux-kernel&m=144785344924871&w=2
The work is static but the worker can be started/stopped
(allocated/freed) repeatedly. It means that the work need
to be usable with many workers. But it is associated only
with one worker when being used.

It can just re-init work items when it restarts workers, right?

Thanks.

-- 
tejun

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