RE: [bluetooth-next V2] Bluetooth: handle device reset event

[Marcel Holtmann <marcel@holtmann.org>]

Hi Tomas,

> > > > > A Bluetooth device experiencing hardware failure may issue
> > > > > a HARDWARE_ERROR hci event. The reaction to this event is device
> > > > > reset flow implemented in following sequence.
> > > > >
> > > > > 1. Notify: HCI_DEV_DOWN
> > > > > 2. Reinitialize internal structures.
> > > > > 3. Call driver flush function
> > > > > 4. Send HCI reset request to the device.
> > > > > 5. Send HCI init sequence reset to the device.
> > > > > 6. Notify HCI_DEV_UP.
> > > >
> > > > I prefer if we create a generic per controller workqueue first before
> > > > having a workqueue for every task. Something similar to what the
> > > > mac80211 layer offers right now.
> > >
> > > That would be good approach but we are using default kernel workqueue in
> > this solution so there is no workqueue for every task.
> > > I'm not sure if this effort should block this patch.
> > 
> > I have an initial patch that I have to dig out. It is actually not that
> > complicated. And I would prefer to get that one first before we apply
> > this patch.
> 
> Okay, I can test this particular flow with your patch if you send it to me.

I pushed the per controller workqueue patch into bluetooth-testing.git
tree. Please adapt your patch to that and test it.

> > The reason why I really wanna solve this is because of potential race
> > conditions between the workqueue and a device removal. I have a bad
> > feeling that even with the current sysfs workqueue we have a race
> > condition hiding somewhere. So if going forward we have to shift more
> > and more code into workqueues we need a single point where this can be
> > fixed.
> 
> Understood.
> 
> In that context I would need to do some more instrumentation to test this kind of race for this feature. 

I could be very well that we are protected against such a race. However
with moving from tasklet into workqueue I am always cautious. And I
wanna make sure that we keep the complexity simple. I want one place to
fix if it breaks and not twenty.

Regards

Marcel