netdev - Re: [PATCH] ath9k: use proper statements in conditionals

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Date:   Fri, 16 Dec 2022 12:16:17 +0100
From:   "Arnd Bergmann" <arnd@...db.de>
To:     Toke Høiland-Jørgensen <toke@...e.dk>,
        "Arnd Bergmann" <arnd@...nel.org>, "Kalle Valo" <kvalo@...nel.org>,
        "Pavel Skripkin" <paskripkin@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        "Eric Dumazet" <edumazet@...gle.com>,
        "Jakub Kicinski" <kuba@...nel.org>,
        "Paolo Abeni" <pabeni@...hat.com>,
        "Tetsuo Handa" <penguin-kernel@...ove.sakura.ne.jp>,
        linux-wireless@...r.kernel.org, Netdev <netdev@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ath9k: use proper statements in conditionals

On Thu, Dec 15, 2022, at 18:16, Toke Høiland-Jørgensen wrote:
>> index 30f0765fb9fd..237f4ec2cffd 100644
>> --- a/drivers/net/wireless/ath/ath9k/htc.h
>> +++ b/drivers/net/wireless/ath/ath9k/htc.h
>> @@ -327,9 +327,9 @@ static inline struct ath9k_htc_tx_ctl *HTC_SKB_CB(struct sk_buff *skb)
>>  }
>>  
>>  #ifdef CONFIG_ATH9K_HTC_DEBUGFS
>> -#define __STAT_SAFE(hif_dev, expr)	((hif_dev)->htc_handle->drv_priv ? (expr) : 0)
>> -#define CAB_STAT_INC(priv)		((priv)->debug.tx_stats.cab_queued++)
>> -#define TX_QSTAT_INC(priv, q)		((priv)->debug.tx_stats.queue_stats[q]++)
>> +#define __STAT_SAFE(hif_dev, expr)	do { ((hif_dev)->htc_handle->drv_priv ? (expr) : 0); } while (0)
>> +#define CAB_STAT_INC(priv)		do { ((priv)->debug.tx_stats.cab_queued++); } while (0)
>> +#define TX_QSTAT_INC(priv, q)		do { ((priv)->debug.tx_stats.queue_stats[q]++); } while (0)
>
> Hmm, is it really necessary to wrap these in do/while constructs? AFAICT
> they're all simple statements already?

It's generally safer to do the same thing on both side of the #ifdef.

The "do { } while (0)" is an empty statement that is needed to fix
the bug on the #else side. The expressions you have on the #ifdef
side can be used as values, and wrapping them in do{}while(0)
turns them into statements (without a value) as well, so fewer
things can go wrong when you only test one side.

I suppose the best solution would be to just use inline functions
for all of them and get rid of the macros.

     Arnd