On 11/24/25 08:42, Jiri Slaby wrote:
Hmm, CCing TTY MAINTAINERS entry would not hurt.
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
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.
--- a/drivers/usb/host/xhci-dbgtty.c +++ b/drivers/usb/host/xhci-dbgtty.c @@ -535,6 +535,12 @@ static void xhci_dbc_tty_unregister_device(struct xhci_dbc *dbc) if (!port->registered) return; + /* + * Hang up the TTY. This wakes up any blocked + * writers and causes subsequent writes to fail. + */ + tty_vhangup(port->port.tty);
This is wrong IMO:
- what if there is no tty currently open? Ie. tty is NULL.
v1 had the NULL check, I stated that tty_port_tty_vhangup() does the check for us so no need for it here.
https://lore.kernel.org/linux-usb/d25feb0d-2ede-4722-a499-095139870c96@linux...
looks like v2 removed the check but used tty_vhangup() instead of tty_port_tty_vhangup()
- 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()
tty internals are still a bit of mystery to me
Thanks Mathias