[PATCH v3] serial: 8250: Clear CON_PRINTBUFFER on port re-registration

[Fushuai Wang <fushuai.wang@linux.dev>]

From: Fushuai Wang <wangfushuai@baidu.com>

When two PnP devices map to the same physical port, the serial8250 driver
removes and re-registers the console structure for the same port.

During re-registration, the console structure still has CON_PRINTBUFFER set
from the initial registration, which causes console_init_seq() to set
console->seq to syslog_seq. This results in re-printing the entire
system log buffer, which may lead to RCU stall on slow serial consoles.

Clear CON_PRINTBUFFER when re-registering a port to prevent duplicate
log printing.

Fixes: 835d844d1a28 ("8250_pnp: do pnp probe before legacy probe")
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Fushuai Wang <wangfushuai@baidu.com>
---
V2->V3: Clear CON_PRINTBUFFER when remove the port
V1->V2: Add Fixes tag

 drivers/tty/serial/8250/8250_core.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index a428e88938eb..5419f1d22d47 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -716,8 +716,12 @@ int serial8250_register_8250_port(const struct uart_8250_port *up)
 	if (uart->port.type == PORT_8250_CIR)
 		return -ENODEV;
 
-	if (uart->port.dev)
+	if (uart->port.dev) {
+		if (uart_console(&uart->port))
+			uart->port.cons->flags &= ~CON_PRINTBUFFER;
+
 		uart_remove_one_port(&serial8250_reg, &uart->port);
+	}
 
 	uart->port.ctrl_id	= up->port.ctrl_id;
 	uart->port.port_id	= up->port.port_id;
-- 
2.36.1