linux-kernel - Re: [PATCH] tty: hvcs: Don't NULL tty->driver_data until hvcs

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Message-ID: <096400db-d454-d254-aa30-437352360f7f@linux.ibm.com>
Date:   Fri, 21 Aug 2020 14:08:46 -0700
From:   Tyrel Datwyler <tyreld@...ux.ibm.com>
To:     gregkh@...uxfoundation.org
Cc:     Jiri Slaby <jirislaby@...nel.org>, Jason Yan <yanaijie@...wei.com>,
        Joe Perches <joe@...ches.com>,
        "open list:HYPERVISOR VIRTUAL CONSOLE DRIVER" 
        <linuxppc-dev@...ts.ozlabs.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tty: hvcs: Don't NULL tty->driver_data until
 hvcs_cleanup()

On 8/20/20 4:46 PM, Tyrel Datwyler wrote:
> The code currently NULLs tty->driver_data in hvcs_close() with the
> intent of informing the next call to hvcs_open() that device needs to be
> reconfigured. However, when hvcs_cleanup() is called we copy hvcsd from
> tty->driver_data which was previoulsy NULLed by hvcs_close() and our
> call to tty_port_put(&hvcsd->port) doesn't actually do anything since
> &hvcsd->port ends up translating to NULL by chance. This has the side
> effect that when hvcs_remove() is called we have one too many port
> references preventing hvcs_destuct_port() from ever being called. This
> also prevents us from reusing the /dev/hvcsX node in a future
> hvcs_probe() and we can eventually run out of /dev/hvcsX devices.
> 
> Fix this by waiting to NULL tty->driver_data in hvcs_cleanup().

I just realized I neglected a Fixes tag.

Fixes: 27bf7c43a19c ("TTY: hvcs, add tty install")

-Tyrel

> 
> Signed-off-by: Tyrel Datwyler <tyreld@...ux.ibm.com>
> ---
>  drivers/tty/hvc/hvcs.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/tty/hvc/hvcs.c b/drivers/tty/hvc/hvcs.c
> index 55105ac38f89..509d1042825a 100644
> --- a/drivers/tty/hvc/hvcs.c
> +++ b/drivers/tty/hvc/hvcs.c
> @@ -1216,13 +1216,6 @@ static void hvcs_close(struct tty_struct *tty, struct file *filp)
>  
>  		tty_wait_until_sent(tty, HVCS_CLOSE_WAIT);
>  
> -		/*
> -		 * This line is important because it tells hvcs_open that this
> -		 * device needs to be re-configured the next time hvcs_open is
> -		 * called.
> -		 */
> -		tty->driver_data = NULL;
> -
>  		free_irq(irq, hvcsd);
>  		return;
>  	} else if (hvcsd->port.count < 0) {
> @@ -1237,6 +1230,13 @@ static void hvcs_cleanup(struct tty_struct * tty)
>  {
>  	struct hvcs_struct *hvcsd = tty->driver_data;
>  
> +	/*
> +	 * This line is important because it tells hvcs_open that this
> +	 * device needs to be re-configured the next time hvcs_open is
> +	 * called.
> +	 */
> +	tty->driver_data = NULL;
> +
>  	tty_port_put(&hvcsd->port);
>  }
>  
>