* Re: [PATCH v2] serial: 8250: Clear CON_PRINTBUFFER on port re-registration
[not found] <20260428090349.30047-1-fushuai.wang@linux.dev>
@ 2026-05-11 15:16 ` Greg KH
0 siblings, 0 replies; only message in thread
From: Greg KH @ 2026-05-11 15:16 UTC (permalink / raw)
To: Fushuai Wang
Cc: jirislaby, ilpo.jarvinen, osama.abdelkader, andy.shevchenko, kees,
linux-kernel, linux-serial, wangfushuai
On Tue, Apr 28, 2026 at 05:03:49PM +0800, Fushuai Wang wrote:
> 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")
> Signed-off-by: Fushuai Wang <wangfushuai@baidu.com>
> ---
> V1->V2: Add Fixes tag
> previous discussion: https://lore.kernel.org/all/20260416092917.27301-1-fushuai.wang@linux.dev/T/#u
>
> Please ignore previous email if you received it before. There is something wrong with my email client.
>
> drivers/tty/serial/8250/8250_core.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> index a428e88938eb..01b14392d9f7 100644
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -694,6 +694,7 @@ int serial8250_register_8250_port(const struct uart_8250_port *up)
> {
> struct uart_8250_port *uart;
> int ret;
> + bool was_removed = false;
>
> if (up->port.uartclk == 0)
> return -EINVAL;
> @@ -716,8 +717,10 @@ 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) {
> uart_remove_one_port(&serial8250_reg, &uart->port);
> + was_removed = true;
> + }
>
> uart->port.ctrl_id = up->port.ctrl_id;
> uart->port.port_id = up->port.port_id;
> @@ -819,6 +822,10 @@ int serial8250_register_8250_port(const struct uart_8250_port *up)
> &uart->capabilities);
>
> serial8250_apply_quirks(uart);
> +
> + if (was_removed && uart_console(&uart->port))
> + uart->port.cons->flags &= ~CON_PRINTBUFFER;
Why not set the flag up above when you remove the port? Why down here?
thanks,
greg k-h
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