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

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Message-ID: <20250814125147.483ff378@pumpkin>
Date: Thu, 14 Aug 2025 12:51:47 +0100
From: David Laight <david.laight.linux@...il.com>
To: David Hildenbrand <david@...hat.com>
Cc: Qingshuang Fu <fffsqian@....com>, akpm@...ux-foundation.org,
 hannes@...xchg.org, mhocko@...nel.org, zhengqi.arch@...edance.com,
 lorenzo.stoakes@...cle.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Qingshuang Fu <fuqingshuang@...inos.cn>
Subject: Re: [PATCH] Fix the data type inconsistency issue of min (tier,
 MAX_CR_TIERS-1) in read_ctrl_pos

On Fri, 8 Aug 2025 09:35:19 +0200
David Hildenbrand <david@...hat.com> wrote:

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

He must be using the pre 6.11-rc2 version of minmax.h

Some of the variables are clearly the wrong type, but min_t() isn't needed
and shouldn't be the fix.
Even the error message tells you to try to fix it differently!

	David