Re: [PATCH 2/4] Bluetooth: Rename _busy_wq to _l2cap_wq

["Gustavo F. Padovan" <padovan@profusion.mobi>]

* Mat Martineau <mathewm@codeaurora.org> [2011-06-09 16:09:52 -0700]:

> 
> On Thu, 9 Jun 2011, Gustavo F. Padovan wrote:
> 
> >* Mat Martineau <mathewm@codeaurora.org> [2011-06-08 16:24:05 -0700]:
> >
> >>
> >>On Mon, 6 Jun 2011, Gustavo F. Padovan wrote:
> >>
> >>>* Mat Martineau <mathewm@codeaurora.org> [2011-06-03 16:21:08 -0700]:
> >>>
> >>>>This workqueue will be used for general L2CAP work, not just dealing
> >>>>with "busy" frames.
> >>>
> >>>which general L2CAP work are we talking about?
> >>
> >>I'll update the commit message and resubmit, but to immediately
> >>answer your question:
> >>
> >>* ERTM tx queue callbacks (patch 3/4 in this series)
> >>* ERTM timers (ack, retrans, monitor) that can utilize proper locking.
> >
> >What are the problems with ERTM timers? From what I remember it was not using
> >reference count on them, I fixed this. Patch is on this mailing for review.
> 
> The ERTM timer handlers modify l2cap_chan data, but use
> bh_lock_sock() and bh_unlock_sock() instead of lock_sock() and
> release_sock().  The socket might be locked in userspace context,
> but these timers can fire and start executing code concurrently.
> 
> See http://article.gmane.org/gmane.linux.bluez.kernel/6808 for the
> full description.
> 
> With the refactoring of L2CAP to separate out the socket code, we
> will still need a per-channel lock to protect l2cap_chan data.

I understand. I'm just having a similar problem with the workqueue patch.

> 
> >>* Updating the ERTM tx queue after an AMP channel move and L2CAP
> >>reconfiguration
> >>* Moving various AMP-related work out of interrupt context
> >
> >Marcel wrote a patch sometime ago the move the whole Bluetooth core work out
> >of the interrupt context. That will help with many issues we have today,
> >including these you are talking about.
> >We need to take that patch, fix it, and push it no bluetooth-next.
> >This task is on my TODO list, but my TODO list is getting bigger. ;)
> 
> This would be a big help, do you have a pointer to this patch? 

http://permalink.gmane.org/gmane.linux.bluez.kernel/6966

It only moves the cmd rx task to workqueue, but it has problems, see the
comments. I took this patches today and changed it to handle all rx events and
data in an workqueue. But it still has a issue with timers, because those run
in interrupt context. I just had no time to think on this, but will tomorrow.

> Is
> the new workqueue accessible for all Bluetooth modules, or is it
> just for the HCI core?  The other issues in my list still need a
> workqueue to use, they are not solved by moving rx processing out of
> interrupt context.  If rx processing gets rid of interrupt context,
> we'll also want to take a close look at all other timer use.

No, but there is a per controller wokqueue. It was added by f48fd9c8cd746.
I think it is good idea reuse it.

	Gustavo