From 84bb4ef6233cddaf10a656f21375d5e008d6751c Mon Sep 17 00:00:00 2001 From: Kuen-Han Tsai Date: Tue, 17 Jun 2025 13:07:12 +0800 Subject: [PATCH] UPSTREAM: usb: gadget: u_serial: Fix race condition in TTY wakeup A race condition occurs when gs_start_io() calls either gs_start_rx() or gs_start_tx(), as those functions briefly drop the port_lock for usb_ep_queue(). This allows gs_close() and gserial_disconnect() to clear port.tty and port_usb, respectively. Use the null-safe TTY Port helper function to wake up TTY. Example CPU1: CPU2: gserial_connect() // lock gs_close() // await lock gs_start_rx() // unlock usb_ep_queue() gs_close() // lock, reset port.tty and unlock gs_start_rx() // lock tty_wakeup() // NPE Fixes: 35f95fd7f234 ("TTY: usb/u_serial, use tty from tty_port") Cc: stable Signed-off-by: Kuen-Han Tsai Reviewed-by: Prashanth K Link: https://lore.kernel.org/linux-usb/20240116141801.396398-1-khtsai@google.com/ Link: https://lore.kernel.org/r/20250617050844.1848232-2-khtsai@google.com Signed-off-by: Greg Kroah-Hartman Bug: 417232809 (cherry picked from commit c529c3730bd09115684644e26bf01ecbd7e2c2c9) Change-Id: I0dfff41aeae526bc3c334266f2773e6636d8dd33 Signed-off-by: Kuen-Han Tsai --- drivers/usb/gadget/function/u_serial.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c index 729b0472bab0..7a306b11881f 100644 --- a/drivers/usb/gadget/function/u_serial.c +++ b/drivers/usb/gadget/function/u_serial.c @@ -291,8 +291,8 @@ __acquires(&port->port_lock) break; } - if (do_tty_wake && port->port.tty) - tty_wakeup(port->port.tty); + if (do_tty_wake) + tty_port_tty_wakeup(&port->port); return status; } @@ -573,7 +573,7 @@ static int gs_start_io(struct gs_port *port) gs_start_tx(port); /* Unblock any pending writes into our circular buffer, in case * we didn't in gs_start_tx() */ - tty_wakeup(port->port.tty); + tty_port_tty_wakeup(&port->port); } else { /* Free reqs only if we are still connected */ if (port->port_usb) {