linux-kernel - Re: [PATCH 33/36] tty/vt: consolemap: change refcount only if needed in con_do_clear

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Date:   Tue, 7 Jun 2022 18:31:54 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Jiri Slaby <jslaby@...e.cz>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-serial <linux-serial@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 33/36] tty/vt: consolemap: change refcount only if needed
 in con_do_clear_unimap()

On Tue, 7 Jun 2022, Jiri Slaby wrote:

> con_do_clear_unimap() currently decreases and increases refcount of old
> dictionary in a back and forth fashion. This makes the code really hard
> to follow. Decrease the refcount only if everything went well and we
> really allocated a new one and decoupled from the old dictionary.
> 
> I sincerelly hope I did not make a mistake in this (ill) logic.
> 
> Signed-off-by: Jiri Slaby <jslaby@...e.cz>

It seems fine:

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

One unrelated comment below for additional cleanup opportunity.

> ---
>  drivers/tty/vt/consolemap.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/tty/vt/consolemap.c b/drivers/tty/vt/consolemap.c
> index 01b7e49f1f91..4d8efe74315c 100644
> --- a/drivers/tty/vt/consolemap.c
> +++ b/drivers/tty/vt/consolemap.c
> @@ -535,22 +535,23 @@ static int con_do_clear_unimap(struct vc_data *vc)
>  {
>  	struct uni_pagedict *old = *vc->vc_uni_pagedir_loc;
>  
> -	if (!old || --old->refcount) {
> +	if (!old || old->refcount > 1) {
>  		struct uni_pagedict *new = kzalloc(sizeof(*new), GFP_KERNEL);
> -		if (!new) {
> -			if (old)
> -				old->refcount++;
> +		if (!new)
>  			return -ENOMEM;
> -		}
> +
>  		new->refcount = 1;
>  		*vc->vc_uni_pagedir_loc = new;
> +
> +		if (old)
> +			old->refcount--;
>  	} else {
>  		if (old == dflt)
>  			dflt = NULL;

This seems unnecessary as con_release_unimap() already does it.

> -		old->refcount++;
>  		old->sum = 0;
>  		con_release_unimap(old);
>  	}
> +
>  	return 0;
>  }
>  
> 

-- 
 i.