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Date:   Thu, 17 Mar 2022 08:06:39 +0100
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Subject: Re: [PATCH v4 5/5] serial/8250: Only use fifo after the port is
 initialized in console_write
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To:     Wander Lairson Costa <wander@redhat.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Johan Hovold <johan@kernel.org>,
        "Maciej W. Rozycki" <macro@orcam.me.uk>,
        Serge Semin <fancer.lancer@gmail.com>,
        Lukas Wunner <lukas@wunner.de>,
        =?UTF-8?Q?Pali_Roh=c3=a1r?= <pali@kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
Cc:     rostedt@goodmis.org, senozhatsky@chromium.org,
        andre.goddard@gmail.com, sudipm.mukherjee@gmail.com,
        andy.shevchenko@gmail.com, David.Laight@aculab.com,
        jonathanh@nvidia.com, phil@raspberrypi.com
References: <20220316143646.13301-1-wander@redhat.com>
 <20220316143646.13301-6-wander@redhat.com>
From:   Jiri Slaby <jirislaby@kernel.org>
In-Reply-To: <20220316143646.13301-6-wander@redhat.com>
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On 16. 03. 22, 15:36, Wander Lairson Costa wrote:
> The serial driver set the value of uart_8250_port.fcr in the function
> serial8250_config_port, but only writes the value to the controller
> register later in the initalization code.
> 
> That opens a small window in which is not safe to use the fifo for
> console write.
> 
> Make sure the port is initialized correctly before reading the FCR
> cached value.
> 
> Unfortunately, I lost track of who originally reported the issue. If
> s/he is reading this, please speak up so I can give you the due credit.
> 
> Signed-off-by: Wander Lairson Costa <wander@redhat.com>
> ---
>   drivers/tty/serial/8250/8250_port.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 4acf620be241..7e2227161555 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -3416,6 +3416,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s,
>   		!(up->capabilities & UART_CAP_MINI) &&
>   		up->tx_loadsz > 1 &&
>   		(up->fcr & UART_FCR_ENABLE_FIFO) &&
> +		test_bit(TTY_PORT_INITIALIZED, &port->state->port.iflags) &&

Cannot be port->state be NULL sometimes here?

>   		/*
>   		 * After we put a data in the fifo, the controller will send
>   		 * it regardless of the CTS state. Therefore, only use fifo


-- 
js
suse labs