[PATCH] serial: 8250: clear RX trigger callbacks when removing a port

[James Hilliard]

serial8250_unregister_port() removes the device supplied by a driver and
normally re-registers the persistent slot as an unknown legacy port. The
slot retains its RX trigger callbacks and sysfs attribute group, so the
replacement rx_trig_bytes attribute can still call the removed driver's
code. Unloading that driver leaves the callbacks pointing into freed
module text.

Clear both callbacks after uart_remove_one_port() has drained the old
sysfs users and before registering the fallback port. Its RX trigger
attribute then uses the generic handlers, which reject a port without
FIFO capabilities.

Also copy the callbacks unconditionally during registration. A replacement
port without custom handlers must use the generic implementation instead
of inheriting callbacks from the previous owner of the slot.

Fixes: 8a6c543cf8b3 ("serial: 8250: allow UART drivers to override rx_trig_bytes handling")
Signed-off-by: James Hilliard <james.hilliard1@xxxxxxxxx>
---
 drivers/tty/serial/8250/8250_core.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 42319843cb5b..c638e10c43e2 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -830,10 +830,8 @@ static int __serial8250_register_8250_port(struct uart_8250_port *uart,
 		uart->port.get_divisor = up->port.get_divisor;
 	if (up->port.set_divisor)
 		uart->port.set_divisor = up->port.set_divisor;
-	if (up->port.get_rxtrig)
-		uart->port.get_rxtrig = up->port.get_rxtrig;
-	if (up->port.set_rxtrig)
-		uart->port.set_rxtrig = up->port.set_rxtrig;
+	uart->port.get_rxtrig = up->port.get_rxtrig;
+	uart->port.set_rxtrig = up->port.set_rxtrig;
 	if (up->port.startup)
 		uart->port.startup = up->port.startup;
 	if (up->port.shutdown)
@@ -953,6 +951,9 @@ void serial8250_unregister_port(struct uart_8250_port *uart)
 	}
 
 	uart_remove_one_port(&serial8250_reg, &uart->port);
+	/* The fallback port must use the generic RX trigger handlers. */
+	uart->port.get_rxtrig = NULL;
+	uart->port.set_rxtrig = NULL;
 	if (serial8250_isa_devs) {
 		uart->port.flags &= ~UPF_BOOT_AUTOCONF;
 		uart->port.type = PORT_UNKNOWN;

---
base-commit: 1184f87e2790e8af9be3116f608d2e86b4792d7d
change-id: 20261024-submit-serial-8250-rxtrig-lifetime-v1-4fa940207ae5

Best regards,
--  
James Hilliard <james.hilliard1@xxxxxxxxx>