[PATCH 1/1] mm: silence data-race in update_hiwater_rss

[PATCH 1/1] mm: silence data-race in update_hiwater_rss

[Lance Yang]

From: Lance Yang <lance.yang@linux.dev>

KCSAN reports a data race on mm_cluster.hiwater_rss, which can be accessed
concurrently from various paths like page migration and memory unmapping
without synchronization.

Since hiwater_rss is a statistical field for accounting purposes, this data
race is benign. Annotate both the read and write accesses with data_race()
to make KCSAN happy.

Reported-by: syzbot+60192c8877d0bc92a92b@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-mm/68d6364e.050a0220.3390a8.000d.GAE@google.com
Signed-off-by: Lance Yang <lance.yang@linux.dev>
---
 include/linux/mm.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6b6c6980f46c..dd93335e3a13 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2757,7 +2757,7 @@ static inline void update_hiwater_rss(struct mm_struct *mm)
 	unsigned long _rss = get_mm_rss(mm);
 
 	if (data_race(mm->hiwater_rss) < _rss)
-		(mm)->hiwater_rss = _rss;
+		data_race(mm->hiwater_rss = _rss);
 }
 
 static inline void update_hiwater_vm(struct mm_struct *mm)
-- 
2.49.0

Re: [PATCH 1/1] mm: silence data-race in update_hiwater_rss

[Vlastimil Babka]

On 9/26/25 11:24, Lance Yang wrote:
> From: Lance Yang <lance.yang@linux.dev>
> 
> KCSAN reports a data race on mm_cluster.hiwater_rss, which can be accessed
> concurrently from various paths like page migration and memory unmapping
> without synchronization.
> 
> Since hiwater_rss is a statistical field for accounting purposes, this data
> race is benign. Annotate both the read and write accesses with data_race()
> to make KCSAN happy.
> 
> Reported-by: syzbot+60192c8877d0bc92a92b@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/linux-mm/68d6364e.050a0220.3390a8.000d.GAE@google.com
> Signed-off-by: Lance Yang <lance.yang@linux.dev>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  include/linux/mm.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 6b6c6980f46c..dd93335e3a13 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2757,7 +2757,7 @@ static inline void update_hiwater_rss(struct mm_struct *mm)
>  	unsigned long _rss = get_mm_rss(mm);
>  
>  	if (data_race(mm->hiwater_rss) < _rss)
> -		(mm)->hiwater_rss = _rss;
> +		data_race(mm->hiwater_rss = _rss);
>  }
>  
>  static inline void update_hiwater_vm(struct mm_struct *mm)

Re: [PATCH 1/1] mm: silence data-race in update_hiwater_rss

[Lorenzo Stoakes]

On Fri, Sep 26, 2025 at 05:24:26PM +0800, Lance Yang wrote:
> From: Lance Yang <lance.yang@linux.dev>
>
> KCSAN reports a data race on mm_cluster.hiwater_rss, which can be accessed
> concurrently from various paths like page migration and memory unmapping
> without synchronization.
>
> Since hiwater_rss is a statistical field for accounting purposes, this data
> race is benign. Annotate both the read and write accesses with data_race()
> to make KCSAN happy.
>
> Reported-by: syzbot+60192c8877d0bc92a92b@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/linux-mm/68d6364e.050a0220.3390a8.000d.GAE@google.com
> Signed-off-by: Lance Yang <lance.yang@linux.dev>

LGTM, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

> ---
>  include/linux/mm.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 6b6c6980f46c..dd93335e3a13 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2757,7 +2757,7 @@ static inline void update_hiwater_rss(struct mm_struct *mm)
>  	unsigned long _rss = get_mm_rss(mm);
>
>  	if (data_race(mm->hiwater_rss) < _rss)
> -		(mm)->hiwater_rss = _rss;
> +		data_race(mm->hiwater_rss = _rss);
>  }
>
>  static inline void update_hiwater_vm(struct mm_struct *mm)
> --
> 2.49.0
>
>