Subject: Re: [PATCH] TTY: hvc_console, fix port reference count going to zero prematurely

From: Jiri Slaby <[email-masked]>
Date: Wed, 14 Nov 2012 10:45:40 +0100

On 11/14/2012 09:15 AM, Paul Mackerras wrote:
> Commit bdb498c20040 "TTY: hvc_console, add tty install" took the port
> refcounting out of hvc_open()/hvc_close(), but failed to remove the
> kref_put() and tty_kref_put() calls in hvc_hangup() that were there to
> remove the extra references that hvc_open() had taken.
> 
> The result was that doing a vhangup() when the current terminal was
> a hvc_console, then closing the current terminal, would end up calling
> destroy_hvc_struct() and making the port disappear entirely.  This
> meant that Fedora 17 systems would boot up but then not display the
> login prompt on the console, and attempts to open /dev/hvc0 would
> give a "No such device" error.
> 
> This fixes it by removing the extra kref_put() and tty_kref_put() calls.

Oh yeah. Thanks.

Acked-by: Jiri Slaby <[email-masked]>

> Signed-off-by: Paul Mackerras <[email-masked]>
> Cc: [email-masked]
> ---
>  drivers/tty/hvc/hvc_console.c |    7 -------
>  1 file changed, 7 deletions(-)
> 
> diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
> index a5dec1c..13ee53b 100644
> --- a/drivers/tty/hvc/hvc_console.c
> +++ b/drivers/tty/hvc/hvc_console.c
> @@ -424,7 +424,6 @@ static void hvc_hangup(struct tty_struct *tty)
>  {
>  	struct hvc_struct *hp = tty->driver_data;
>  	unsigned long flags;
> -	int temp_open_count;
>  
>  	if (!hp)
>  		return;
> @@ -444,7 +443,6 @@ static void hvc_hangup(struct tty_struct *tty)
>  		return;
>  	}
>  
> -	temp_open_count = hp->port.count;
>  	hp->port.count = 0;
>  	spin_unlock_irqrestore(&hp->port.lock, flags);
>  	tty_port_tty_set(&hp->port, NULL);
> @@ -453,11 +451,6 @@ static void hvc_hangup(struct tty_struct *tty)
>  
>  	if (hp->ops->notifier_hangup)
>  		hp->ops->notifier_hangup(hp, hp->data);
> -
> -	while(temp_open_count) {
> -		--temp_open_count;
> -		tty_port_put(&hp->port);
> -	}
>  }
>  
>  /*
> 

-- 
js
suse labs