Re: [PATCH 3/8] Move device initialization and shutdown to tty_port_operations

[Gianluca Anzolin <gianluca@sottospazio.it>]

On Sun, Jul 21, 2013 at 01:04:03PM -0400, Peter Hurley wrote:
> On 07/21/2013 04:08 AM, Gianluca Anzolin wrote:
> >On Sat, Jul 20, 2013 at 10:11:50AM -0400, Peter Hurley wrote:
> >>Sorry Gianluca, I should have been more specific here.
> >>
> >>There's no need to test for dlc->state == BT_CLOSED in carrier_raised().
> >>At the point where port->carrier_raised is called, the tty will have been
> >>linked with the file descriptor, so if the dlc->state goes to BT_CLOSED,
> >>then rfcomm_dev_state_change() will call
> >>   tty_hangup() -> driver hangup() -> tty_port_hangup() -> tty_port_shutdown()
> >>This call chain will
> >>   1. set the file_ops to hung_up_tty_fops which will cause tty_hung_up_p() to
> >>      return true
> >>   2. clear ASYNCB_INITIALIZED in port->flags
> >>   3. wakeup port->open_wait
> >>
> >>So an open() parked in the schedule loop of tty_port_block_til_ready()
> >>will wake and exit the loop with either -EAGAIN or -ERESTARTSYS.
> >>
> >>rfcomm_dev_state_change() should only do a wakeup on port->open_wait when
> >>dlc->state == BT_CONNECTED.
> >>
> >>>In case of success I should also call some device_move,
> >>>rfcomm_tty_copy_pending and rfcomm_dlc_unthrottle. Could I do it in
> >>>carrier_raised directly?
> >>
> >>I wouldn't. That would be a nasty hack and a potential problem if a
> >>signal occurred.
> >>
> >>The device_move() isn't dependent on success, and can stay in .activate().
> >
> >I changed the code and it's cleaner than before, very nice. However the
> >device_move() is really dependent on success: the parent device is there only
> >when the connection has been successfully established.
> 
> Oh, right.
> 
> >So I have to call that function after the carrier is raised, or right before.
> >Since you already told me that calling it in the .carrier_raised method is
> >unwise the only place left is the state_change callback of the dlc.
> 
> That seems fine. [ Another place would be in rfcomm_tty_open() just after
> tty_port_open() returns success -- the tty is still locked here so it won't
> race with .close/.hangup() ]

I will do it in state_change because open could be called multiple times by
several user space programs.

> 
> I do wonder why the tty device is re-parented to the host controller device.
> It's obviously not for subsystem teardown. Maybe one of the bluetooth
> maintainers could clarify this? Are there userspace components waiting for
> this uevent?
> 
> >Conversely in .shutdown the check for the device parent == NULL takes care of
> >the scenario in which the aforementioned device_move() is never called.
> >
> >Another unrelated question: I'm working on the rfcomm_dev_add function to avoid
> >the two nested locks. When the patch is ready should I send it separately or
> >can I include it with the other patches?
> 
> Your preference.
> 
> Just a reminder: the dlc lock will still need to be dropped after bumping the
> rfcomm_dev ref count via rfcomm_dev_get(), because when you subsequently drop
> both references, rfcomm_dev destruction will attempt to gain the dlc lock,
> resulting in deadlock. [Or do it as a work item]

Yes I noticed that and before the last tty_port_put I will unlock the dlc.

> 
> Regards,
> Peter Hurley
> 

Thanks,

Gianluca