linux-kernel - Re: [PATCH 1/2] serial: 8250: Use 'hlist_for_each

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Date:   Wed, 28 Apr 2021 12:05:26 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     gregkh@...uxfoundation.org, jirislaby@...nel.org, lukas@...ner.de,
        yangyingliang@...wei.com, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 1/2] serial: 8250: Use 'hlist_for_each_entry' to simplify
 code

On Wed, Apr 28, 2021 at 09:30:40AM +0200, Christophe JAILLET wrote:
> Use 'hlist_for_each_entry' instead of hand writing it.
> This saves a few lines of code.
> 
> The comment about warning generated by some gcc version is also removed.
> The way 'hlist_for_each_entry' is written should prevent such a warning to
> be emitted.

I checked the implementation of the macros vs. this usage and below seems legit.
However it indeed needs more test coverage because it's sensitive piece of code.

FWIW,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

(with the above caveat)

> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
> Compile tested only
> ---
>  drivers/tty/serial/8250/8250_core.c | 18 ++++--------------
>  1 file changed, 4 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> index cae61d1ebec5..081b773a54c9 100644
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -172,7 +172,6 @@ static void serial_do_unlink(struct irq_info *i, struct uart_8250_port *up)
>  static int serial_link_irq_chain(struct uart_8250_port *up)
>  {
>  	struct hlist_head *h;
> -	struct hlist_node *n;
>  	struct irq_info *i;
>  	int ret;
>  
> @@ -180,13 +179,11 @@ static int serial_link_irq_chain(struct uart_8250_port *up)
>  
>  	h = &irq_lists[up->port.irq % NR_IRQ_HASH];
>  
> -	hlist_for_each(n, h) {
> -		i = hlist_entry(n, struct irq_info, node);
> +	hlist_for_each_entry(i, h, node)
>  		if (i->irq == up->port.irq)
>  			break;
> -	}
>  
> -	if (n == NULL) {
> +	if (i == NULL) {
>  		i = kzalloc(sizeof(struct irq_info), GFP_KERNEL);
>  		if (i == NULL) {
>  			mutex_unlock(&hash_mutex);
> @@ -220,25 +217,18 @@ static int serial_link_irq_chain(struct uart_8250_port *up)
>  
>  static void serial_unlink_irq_chain(struct uart_8250_port *up)
>  {
> -	/*
> -	 * yes, some broken gcc emit "warning: 'i' may be used uninitialized"
> -	 * but no, we are not going to take a patch that assigns NULL below.
> -	 */
>  	struct irq_info *i;
> -	struct hlist_node *n;
>  	struct hlist_head *h;
>  
>  	mutex_lock(&hash_mutex);
>  
>  	h = &irq_lists[up->port.irq % NR_IRQ_HASH];
>  
> -	hlist_for_each(n, h) {
> -		i = hlist_entry(n, struct irq_info, node);
> +	hlist_for_each_entry(i, h, node)
>  		if (i->irq == up->port.irq)
>  			break;
> -	}
>  
> -	BUG_ON(n == NULL);
> +	BUG_ON(i == NULL);
>  	BUG_ON(i->head == NULL);
>  
>  	if (list_empty(i->head))
> -- 
> 2.30.2
> 

-- 
With Best Regards,
Andy Shevchenko