linux-kernel - Re: [PATCH] cw1200: remove an unneeded NULL check on list iterator

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Message-Id: <EFA8A102-59B2-4FC6-AB2E-CA8311E11635@gmail.com>
Date:   Sun, 20 Mar 2022 01:47:26 +0100
From:   Jakob Koschel <jakobkoschel@...il.com>
To:     Xiaomeng Tong <xiam0nd.tong@...il.com>
Cc:     pizza@...ftnet.org, kvalo@...nel.org, davem@...emloft.net,
        kuba@...nel.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cw1200: remove an unneeded NULL check on list iterator



> On 19. Mar 2022, at 07:38, Xiaomeng Tong <xiam0nd.tong@...il.com> wrote:
> 
> The list iterator 'item' is always non-NULL so it doesn't need to be
> checked. Thus just remove the unnecessary NULL check. Also remove the
> unnecessary initializer because the list iterator is always initialized.
> 
> Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
> ---
> drivers/net/wireless/st/cw1200/queue.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/st/cw1200/queue.c b/drivers/net/wireless/st/cw1200/queue.c
> index 12952b1c29df..05392598e273 100644
> --- a/drivers/net/wireless/st/cw1200/queue.c
> +++ b/drivers/net/wireless/st/cw1200/queue.c
> @@ -90,7 +90,7 @@ static void __cw1200_queue_gc(struct cw1200_queue *queue,
> 			      bool unlock)
> {
> 	struct cw1200_queue_stats *stats = queue->stats;
> -	struct cw1200_queue_item *item = NULL, *tmp;
> +	struct cw1200_queue_item *item, *tmp;
> 	bool wakeup_stats = false;
> 
> 	list_for_each_entry_safe(item, tmp, &queue->queue, head) {
> @@ -117,7 +117,7 @@ static void __cw1200_queue_gc(struct cw1200_queue *queue,
> 			queue->overfull = false;
> 			if (unlock)
> 				__cw1200_queue_unlock(queue);
> -		} else if (item) {
> +		} else {

I don't think this is fixing anything here. You are basically just removing
a check that was always true.

I'm pretty sure that this check is here to check if either the list is empty or no
element was found. If I'm not wrong, some time ago, lists where not circular but
actually pointed to NULL (or the head was NULL) so this check made sense but doesn't
anymore.

The appropriate fix would be only setting 'item' when a break is hit and keep
the original check.

> 			unsigned long tmo = item->queue_timestamp + queue->ttl;
> 			mod_timer(&queue->gc, tmo);
> 			cw1200_pm_stay_awake(&stats->priv->pm_state,
> -- 
> 2.17.1
> 
> 

I've made those changes already and I'm in the process of upstreaming them in an organized
way, so maybe it would make sense to synchronize, so we don't post duplicate patches.

        Jakob