linux-kernel - [PATCH 1/1] mm: silence data-race in update_hiwater

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Message-ID: <20250926092426.43312-1-lance.yang@linux.dev>
Date: Fri, 26 Sep 2025 17:24:26 +0800
From: Lance Yang <lance.yang@...ux.dev>
To: akpm@...ux-foundation.org
Cc: elver@...gle.com,
	Liam.Howlett@...cle.com,
	david@...hat.com,
	harry.yoo@...cle.com,
	jannh@...gle.com,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	lorenzo.stoakes@...cle.com,
	riel@...riel.com,
	syzkaller-bugs@...glegroups.com,
	vbabka@...e.cz,
	syzbot+60192c8877d0bc92a92b@...kaller.appspotmail.com,
	Lance Yang <lance.yang@...ux.dev>
Subject: [PATCH 1/1] mm: silence data-race in update_hiwater_rss

From: Lance Yang <lance.yang@...ux.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@...kaller.appspotmail.com
Closes: https://lore.kernel.org/linux-mm/68d6364e.050a0220.3390a8.000d.GAE@google.com
Signed-off-by: Lance Yang <lance.yang@...ux.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