Re: [PATCH 2/2] kthread_worker: reimplement flush_kthread_work()to allow freeing the work item being executed

[Tejun Heo]

Hello,

On Sat, Jul 21, 2012 at 02:20:06PM -0400, Andy Walls wrote:
> > +	worker->current_work = work;
> >  	spin_unlock_irq(&worker->lock);
> >  
> >  	if (work) {
> >  		__set_current_state(TASK_RUNNING);
> >  		work->func(work);
> 
> If the call to 'work->func(work);' frees the memory pointed to by
> 'work', 'worker->current_work' points to deallocated memory.
> So 'worker->current_work' will only ever used as a unique 'work'
> identifier to handle, correct?

Yeah.  flush_kthread_work(@work) which can only be called if @work is
known to be alive looks at the pointer to determine whether it's the
current work item on the worker.

> >  void flush_kthread_work(struct kthread_work *work)
> >  {
> > -	int seq = work->queue_seq;
> > +	struct kthread_flush_work fwork = {
> > +		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
> > +		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
> > +	};
> > +	struct kthread_worker *worker;
> > +	bool noop = false;
> > +
> 
> You might want a check for 'work == NULL' here, to gracefully handle
> code like the following:
> 
> void driver_work_handler(struct kthread_work *work)
> {
> 	...
> 	kfree(work);
> }
> 
> struct kthread_work *driver_queue_batch(void)
> {
> 	struct kthread_work *work = NULL;
> 	...
> 	while (driver_more_stuff_todo()) {
> 		work = kzalloc(sizeof(struct kthread work), GFP_WHATEVER);
> 		...
> 		queue_kthread_work(&driver_worker, work);
> 	}
> 	return work;
> }
> 
> void driver_foobar(void)
> {
> 	...
> 	flush_kthread_work(driver_queue_batch());
> 	...
> }

workqueue's flush_work() doesn't allow %NULL pointer.  I don't want to
make the behaviors deviate and don't see much point in changing
workqueue's behavior at this point.

Thanks.

-- 
tejun
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