linux-kernel - [PATCH] mm/slub: mark racy accesses on slab->slabs

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Date: Sat,  9 Mar 2024 15:48:56 +0800
From: linke li <lilinke99@...com>
To: 
Cc: lilinke99@...com,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Hyeonggon Yoo <42.hyeyoo@...il.com>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] mm/slub: mark racy accesses on slab->slabs

The reads of slab->slabs are racy because it may be changed by 
put_cpu_partial concurrently. And in slabs_cpu_partial_show ->slabs is
only used for output. Data-racy reads from shared variables that are used
only for diagnostic purposes should typically use data_race(), since it 
is normally not a problem if the values are off by a little.

This patch is aimed at reducing the number of benign races reported by 
KCSAN in order to focus future debugging effort on harmful races.

Signed-off-by: linke li <lilinke99@...com>
---
 mm/slub.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 2ef88bbf56a3..7b20591e7f8a 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -6257,7 +6257,7 @@ static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf)
 		slab = slub_percpu_partial(per_cpu_ptr(s->cpu_slab, cpu));
 
 		if (slab)
-			slabs += slab->slabs;
+			slabs += data_race(slab->slabs);
 	}
 #endif
 
@@ -6271,7 +6271,7 @@ static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf)
 
 		slab = slub_percpu_partial(per_cpu_ptr(s->cpu_slab, cpu));
 		if (slab) {
-			slabs = READ_ONCE(slab->slabs);
+			slabs = data_race(slab->slabs);
 			objects = (slabs * oo_objects(s->oo)) / 2;
 			len += sysfs_emit_at(buf, len, " C%d=%d(%d)",
 					     cpu, objects, slabs);
-- 
2.39.3 (Apple Git-146)