Re: [PATCH] Fix the data type inconsistency issue of min (tier, MAX_CR_TIERS-1) in read_ctrl_pos

[David Hildenbrand <david@redhat.com>]

On 08.08.25 09:21, Qingshuang Fu wrote:
> From: Qingshuang Fu <fuqingshuang@kylinos.cn>

Subject should probably be

"mm/vmscan: fix build bug in read_ctrl_pos"

> 
> Due to the fact that the tier data type in min (tier, MAX_CR_TIERS -1)
> is int,but MAX_CR_TIERS is an unsigned type, directly using
> the min function for comparison will result in an error:
> from mm/vmscan.c:15:
> mm/vmscan.c: In function ‘read_ctrl_pos’:
> ./include/linux/build_bug.h:78:41: error: static assertion failed:
> "min(tier, 4U - 1) signedness error, fix types or
> consider umin() before min_t()"
> And MAX_CR_TIERS is a macro definition defined as 4U,
> so min_t can be used to convert it to int type before
> performing the minimum value operation.
> 

Please use empty lines to make the description easier to read. Also, I 
think you can simplify this heavily.

We should add

Fixes: 37a260870f2c ("mm/mglru: rework type selection")

BUT

this commit is more than half a year old. How come no built bot 
complained about that?

IOW, what compiler are you using and why are only you able to trigger this>

> Signed-off-by: Qingshuang Fu <fuqingshuang@kylinos.cn>
> ---
>   mm/vmscan.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 7de11524a936..f991196fd8e5 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3194,7 +3194,7 @@ static void read_ctrl_pos(struct lruvec *lruvec, int type, int tier, int gain,
>   	pos->gain = gain;
>   	pos->refaulted = pos->total = 0;
>   
> -	for (i = tier % MAX_NR_TIERS; i <= min(tier, MAX_NR_TIERS - 1); i++) {
> +	for (i = tier % MAX_NR_TIERS; i <= min_t(int, tier, MAX_NR_TIERS - 1); i++) {
>   		pos->refaulted += lrugen->avg_refaulted[type][i] +
>   				  atomic_long_read(&lrugen->refaulted[hist][type][i]);
>   		pos->total += lrugen->avg_total[type][i] +


-- 
Cheers,

David / dhildenb