linux-kernel - Re: [PATCH] mm/vmstat: Fix -Wenum-enum-conversion warning in vmstat.h

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Message-ID: <ZwRA9SOcOjjLJcpi@google.com>
Date: Mon, 7 Oct 2024 20:13:41 +0000
From: Aleksei Vetrov <vvvvvv@...gle.com>
To: Shivamurthy Shastri <shivamurthy.shastri@...utronix.de>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	akpm@...ux-foundation.org, vbabka@...e.cz, willy@...radead.org,
	hannes@...xchg.org, anna-maria@...utronix.de, tglx@...utronix.de,
	nathan@...nel.org
Subject: Re: [PATCH] mm/vmstat: Fix -Wenum-enum-conversion warning in vmstat.h

Hi Shivamurthy,

On Fri, Jun 21, 2024 at 01:16:04PM +0200, Shivamurthy Shastri wrote:
> A W=1 build with -Wenum-enum-conversion enabled, results in the
> following build warning due to an arithmetic operation between different
> enumeration types 'enum node_stat_item' and 'enum lru_list':
> 
>   include/linux/vmstat.h:514:36: warning: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Wenum-enum-conversion]
>     514 |         return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
>         |                               ~~~~~~~~~~~ ^ ~~~
> 
> Address this by casting lru to the proper type.
> 
> Signed-off-by: Shivamurthy Shastri <shivamurthy.shastri@...utronix.de>
> Reviewed-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
> ---
>  include/linux/vmstat.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
> index 735eae6e272c..72ecd46fd0c4 100644
> --- a/include/linux/vmstat.h
> +++ b/include/linux/vmstat.h
> @@ -511,7 +511,7 @@ static inline const char *node_stat_name(enum node_stat_item item)
>  
>  static inline const char *lru_list_name(enum lru_list lru)
>  {
> -	return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
> +	return node_stat_name(NR_LRU_BASE + (enum node_stat_item)lru) + 3; // skip "nr_"
>  }
>  
>  static inline const char *writeback_stat_name(enum writeback_stat_item item)
> -- 
> 2.34.1
> 

We have encountered the same problem after trying to update Clang to the
latest version and this is a blocker because we use W=1 to compile the
kernel.

Do you plan to address review comments about casting to int instead of
enum node_stat_item? Or I can submit another patch myself that addresses
it.