On Mon 2015-11-23 13:36:06, Corey Minyard wrote:
>
>
> On 11/18/2015 07:25 AM, Petr Mladek wrote:
> > Kthreads are currently implemented as an infinite loop. Each
> > has its own variant of checks for terminating, freezing,
> > awakening. In many cases it is unclear to say in which state
> > it is and sometimes it is done a wrong way.
> >
> > The plan is to convert kthreads into kthread_worker or workqueues
> > API. It allows to split the functionality into separate operations.
> > It helps to make a better structure. Also it defines a clean state
> > where no locks are taken, IRQs blocked, the kthread might sleep
> > or even be safely migrated.
> >
> > The kthread worker API is useful when we want to have a dedicated
> > single thread for the work. It helps to make sure that it is
> > available when needed. Also it allows a better control, e.g.
> > define a scheduling priority.
> >
> > This patch converts kipmi kthread into the kthread worker API because
> > it modifies the scheduling priority. The change is quite straightforward.
>
> I think this is correct. That code was hard to get right, but I don't
> see where any
> logic is actually changed.
I believe that it was hard to make it working.
> This also doesn't really look any simpler (you end up with more LOC than
> you did before :) ),
> though it will make things more consistent and reduce errors and that's
> a good thing.
I have just realized that the original code actually looks racy. For
example, it does:
__set_current_state(TASK_INTERRUPTIBLE);
schedule();
without rechecking the state in between. There might already be a new
message and it might miss the wake_up_process(). Similar problem is
with the schedule_timeout_interruptible(100); I mean:
CPU 0 CPU 1
ipmi_thread()
spin_lock_irqsave();
smi_result = smi_event_handler();
spin_unlock_irqrestore();
[...]
else if (smi_result == SI_SM_IDLE)
/* true */
if (atomic_read(need_watch)) {
/* true */
sender()
spin_lock_irqsave()
check_start_timer_thread()
wake_up_process()
/*
* NOPE because kthread
* is not sleeping
*/
schedule_timeout_interruptible(100);
/*
* We sleep 100 jiffies but
* there is a pending message.
*/
This is not a problem with the kthread worker API because
mod_delayed_kthread_work(smi_info->worker,
&smi_info->work, 0);
would queue the work to be done immediately and
queue_delayed_kthread_work(smi_info->worker,
&smi_info->work, 100);
would do nothing in this case.
> My only comment is I would like the worker function named ipmi_worker,
> not ipmi_func.
You probably want it because the original name was ipmi_thread. But
it might cause confusion with new_smi->worker. The function gets
assigned to work->func, see struct kthread_work. Therefore I think that
_func suffix makes more sense.
> Reviewed-by: Corey Minyard <cminyard@xxxxxxxxxx>
Thanks a lot for review,
Petr
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