Re: [PATCH v2] xhci: dbgtty: fix device unregister

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Nov 25, 2025 at 08:53:17AM +0100, Łukasz Bartosik wrote:
> On Mon, Nov 24, 2025 at 10:11 AM Jiri Slaby <jirislaby@kernel.org> wrote:
> >
> > On 24. 11. 25, 8:48, Mathias Nyman wrote:
> > > On 11/24/25 08:42, Jiri Slaby wrote:
> > >> Hmm, CCing TTY MAINTAINERS entry would not hurt.
> > >>
> 
> Fair point. I will keep it in mind in the future.
> 
> > >> On 19. 11. 25, 22:29, Łukasz Bartosik wrote:
> > >>> From: Łukasz Bartosik <ukaszb@chromium.org>
> > >>>
> > >>> When DbC is disconnected then xhci_dbc_tty_unregister_device()
> > >>> is called. However if there is any user space process blocked
> > >>> on write to DbC terminal device then it will never be signalled
> > >>> and thus stay blocked indifinitely.
> > >>
> > >> indefinitely
> > >>
> 
> Thanks for spotting this.
> 
> > >>> This fix adds a tty_vhangup() call in xhci_dbc_tty_unregister_device().
> > >>> The tty_vhangup() wakes up any blocked writers and causes subsequent
> > >>> write attempts to DbC terminal device to fail.
> > >>>
> > >>> Cc: stable@vger.kernel.org
> > >>> Fixes: dfba2174dc42 ("usb: xhci: Add DbC support in xHCI driver")
> > >>> Signed-off-by: Łukasz Bartosik <ukaszb@chromium.org>
> > >>> ---
> > >>> Changes in v2:
> > >>> - Replaced tty_hangup() with tty_vhangup()
> > >>
> > >> Why exactly?
> > >
> > > I recommended using tty_vhangup(), well actually tty_port_tty_vhangup()
> > > to solve
> > > issue '2' you pointed out.
> > > To me it looks like tty_vhangup() is synchronous so it won't schedule
> > > hangup work
> > > and should be safe to call right before we destroy the port.
> >
> > Oops, right, my cscope DB was old and lead me to tty_hangup() instead
> > (that schedules).
> >
> > >> 2) you schedule a tty hangup work and destroy the port right after:
> > >>>       tty_unregister_device(dbc_tty_driver, port->minor);
> > >>>       xhci_dbc_tty_exit_port(port);
> > >>>       port->registered = false;
> > >> You should to elaborate how this is supposed to work?
> > >
> > > Does tty_port_tty_vhangup() work here? it
> > > 1. checks if tty is NULL
> > > 2. is synchronous and should be safe to call before tty_unregister_device()
> >
> > Yes, this works for me.
> >
> 
> Greg should I send v3 with typo fix  indifinitely -> indefinitely and
> elaborate on
> the tty_hangup() -> tty_vhangup() replacement in changes ?

As this is already in my tree, a fixup on top of that would be good.

thanks,

greg k-h