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Date: Thu, 4 Apr 2024 09:54:15 +0300
From: Tony Lindgren <tony@atomide.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: kernel test robot <oliver.sang@intel.com>,
	Yicong Yang <yangyicong@hisilicon.com>, oe-lkp@lists.linux.dev,
	lkp@intel.com, linux-kernel@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable <stable@kernel.org>, linux-serial@vger.kernel.org
Subject: Re: [linus:master] [serial]  43066e3222:
 BUG:kernel_NULL_pointer_dereference,address
Message-ID: <20240404065415.GO5132@atomide.com>
References: <202404031607.2e92eebe-lkp@intel.com>
 <Zg1hBvRAxifo50sf@smile.fi.intel.com>
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* Andy Shevchenko <andriy.shevchenko@linux.intel.com> [240403 14:00]:
> Probably we need to check if the port is still open...
> 
> P.S. AFAIU the state / xmit is invalid pointer or so.
> 
> Culprit line:	serial_out(up, UART_TX, xmit->buf[xmit->tail]);

Maybe we can set UPF_DEAD a bit earlier as below?

Regards,

Tony

8< ---------------------------
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -3442,8 +3442,6 @@ void serial_core_unregister_port(struct uart_driver *drv, struct uart_port *port
 
 	mutex_lock(&port_mutex);
 
-	port->flags |= UPF_DEAD;
-
 	serial_core_remove_one_port(drv, port);
 
 	/* Note that struct uart_port *port is no longer valid at this point */
diff --git a/drivers/tty/serial/serial_port.c b/drivers/tty/serial/serial_port.c
index 22b9eeb23e68a..1571ef721ef10 100644
--- a/drivers/tty/serial/serial_port.c
+++ b/drivers/tty/serial/serial_port.c
@@ -104,6 +104,7 @@ EXPORT_SYMBOL(uart_add_one_port);
 
 void uart_remove_one_port(struct uart_driver *drv, struct uart_port *port)
 {
+	port->flags |= UPF_DEAD;
 	serial_ctrl_unregister_port(drv, port);
 }
 EXPORT_SYMBOL(uart_remove_one_port);