Sorry about the late reply.
On Thu, Nov 05, 2020 at 10:17:13PM -0800, Davidlohr Bueso wrote:
> On Thu, 05 Nov 2020, Johan Hovold wrote:
> >On Wed, Nov 04, 2020 at 04:13:07PM -0800, Davidlohr Bueso wrote:
> >> Also, but not strictly related to this. What do you think of deferring all
> >> work in write_parport_reg_nonblock() unconditionally? I'd like to avoid
> >> that mutex_trylock() because eventually I'll be re-adding a warn in the
> >> locking code, but that would also simplify the code done here in the
> >> nonblocking irq write. I'm not at all familiar with parport, but I would
> >> think that restore_state context would not care.
> >
> >Sounds good to me. As long as the state is restored before submitting
> >further requests we should be fine. That would even allow getting rid of
> >write_parport_reg_nonblock() as you can restore the state using
> >synchronous calls from the worker thread. Should simplify things quite a
> >bit.
>
> What about something like the below (probably buggy)? I avoided messing with
> the completion in the work callback, like what prologue/epilogue does for all
> other synchronous calls, because when releasing we sync the work anyway and we
> need to account for scenarios where the work is scheduled but yet not running,
> so it would not be the best fit. And this also makes the flush_work() always
> wait for both writes, otherwise I was having the thread locklessly busy-wait
> on a flag that was set until both write_parport_reg_nonblock() calls returned
> before the flush such that all potential scheduled work was observed. Unless
> I missed something, the cleanup is considerable.
Yeah, I wouldn't bother with the completion, looks broken anyway as
nothing prevent two parport calls from interfering with each other it
seems.
[...]
> /*
> * This is the the common top part of all parallel port callback operations
> that
> * send synchronous messages to the device. This implements convoluted
> locking
> @@ -458,6 +281,10 @@ static int parport_prologue(struct parport *pp)
> reinit_completion(&mos_parport->syncmsg_compl);
> spin_unlock(&release_lock);
>
> + /* ensure writes from restore are submitted before new requests */
> + if (work_pending(&mos_parport->work))
> + flush_work(&mos_parport->work);
> +
> mutex_lock(&mos_parport->serial->disc_mutex);
> if (mos_parport->serial->disconnected) {
> /* device disconnected */
> @@ -482,6 +309,28 @@ static inline void parport_epilogue(struct parport *pp)
> complete(&mos_parport->syncmsg_compl);
> }
>
> +static void deferred_restore_writes(struct work_struct *work)
> +{
> + struct mos7715_parport *mos_parport;
> +
> + mos_parport = container_of(work, struct mos7715_parport, work);
> +
> + mutex_lock(&mos_parport->serial->disc_mutex);
> +
> + /* if device disconnected, game over */
> + if (mos_parport->serial->disconnected) {
> + mutex_unlock(&mos_parport->serial->disc_mutex);
> + return;
> + }
> +
> + write_mos_reg(mos_parport->serial, dummy, MOS7720_DCR,
> + mos_parport->shadowDCR);
> + write_mos_reg(mos_parport->serial, dummy, MOS7720_ECR,
> + mos_parport->shadowECR);
> + kref_put(&mos_parport->ref_count, destroy_mos_parport);
> + mutex_unlock(&mos_parport->serial->disc_mutex);
> +}
> +
> static void parport_mos7715_write_data(struct parport *pp, unsigned char d)
> {
> struct mos7715_parport *mos_parport = pp->private_data;
> @@ -639,12 +488,12 @@ static void parport_mos7715_restore_state(struct
> parport *pp,
> spin_unlock(&release_lock);
> return;
> }
> + kref_get(&mos_parport->ref_count);
I think can do away with the reference count too as you flush the work
before dropping the final reference in release().
> mos_parport->shadowDCR = s->u.pc.ctr;
> mos_parport->shadowECR = s->u.pc.ecr;
> - write_parport_reg_nonblock(mos_parport, MOS7720_DCR,
> - mos_parport->shadowDCR);
> - write_parport_reg_nonblock(mos_parport, MOS7720_ECR,
> - mos_parport->shadowECR);
> +
> + /* defer synchronous writes outside of irq */
> + schedule_work(&mos_parport->work);
> spin_unlock(&release_lock);
> }
>
> @@ -714,12 +563,9 @@ static int mos7715_parport_init(struct usb_serial
> *serial)
>
> mos_parport->msg_pending = false;
> kref_init(&mos_parport->ref_count);
> - spin_lock_init(&mos_parport->listlock);
> - INIT_LIST_HEAD(&mos_parport->active_urbs);
> - INIT_LIST_HEAD(&mos_parport->deferred_urbs);
> usb_set_serial_data(serial, mos_parport); /* hijack private pointer */
> mos_parport->serial = serial;
> - tasklet_setup(&mos_parport->urb_tasklet, send_deferred_urbs);
> + INIT_WORK(&mos_parport->work, deferred_restore_writes);
> init_completion(&mos_parport->syncmsg_compl);
>
> /* cycle parallel port reset bit */
> @@ -1869,8 +1715,6 @@ static void mos7720_release(struct usb_serial *serial)
>
> if (le16_to_cpu(serial->dev->descriptor.idProduct)
> == MOSCHIP_DEVICE_ID_7715) {
> - struct urbtracker *urbtrack;
> - unsigned long flags;
> struct mos7715_parport *mos_parport =
> usb_get_serial_data(serial);
>
> @@ -1888,16 +1732,8 @@ static void mos7720_release(struct usb_serial *serial)
> usb_set_serial_data(serial, NULL);
> mos_parport->serial = NULL;
>
> - /* if tasklet currently scheduled, wait for it to complete */
> - tasklet_kill(&mos_parport->urb_tasklet);
> -
> - /* unlink any urbs sent by the tasklet */
> - spin_lock_irqsave(&mos_parport->listlock, flags);
> - list_for_each_entry(urbtrack,
> - &mos_parport->active_urbs,
> - urblist_entry)
> - usb_unlink_urb(urbtrack->urb);
> - spin_unlock_irqrestore(&mos_parport->listlock, flags);
> + /* if work is currently scheduled, wait for it to complete */
> + cancel_work_sync(&mos_parport->work);
But this must be done before clearing mos_parport->serial above or you
can hit a NULL deref in the worker. Cancel, or flush as Oliver
suggested, after deregistering the port.
> parport_del_port(mos_parport->pp);
>
> kref_put(&mos_parport->ref_count, destroy_mos_parport);
Very nice to see this cleaned up.
Johan
