[PATCH] mm/slub: mark racy access on slab->freelist

[PATCH] mm/slub: mark racy access on slab->freelist

[linke li]

In deactivate_slab(), slab->freelist can be changed concurrently. Mark
data race on slab->freelist as benign using READ_ONCE.

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@qq.com>
---
 mm/slub.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slub.c b/mm/slub.c
index 0d700f6ca547..bb0e05a321e9 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2813,7 +2813,7 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab,
 	struct slab new;
 	struct slab old;
 
-	if (slab->freelist) {
+	if (READ_ONCE(slab->freelist)) {
 		stat(s, DEACTIVATE_REMOTE_FREES);
 		tail = DEACTIVATE_TO_TAIL;
 	}
-- 
2.39.3 (Apple Git-146)

Re: [PATCH] mm/slub: mark racy access on slab->freelist

[David Rientjes]

On Sat, 27 Apr 2024, linke li wrote:

> In deactivate_slab(), slab->freelist can be changed concurrently. Mark
> data race on slab->freelist as benign using READ_ONCE.
> 
> This patch is aimed at reducing the number of benign races reported by
> KCSAN in order to focus future debugging effort on harmful races.
> 

Thanks!  Do you have a data race report to copy+paste into the commit 
description so people can search for it if they stumble across the same 
thing?

> Signed-off-by: linke li <lilinke99@qq.com>
> ---
>  mm/slub.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 0d700f6ca547..bb0e05a321e9 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2813,7 +2813,7 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab,
>  	struct slab new;
>  	struct slab old;
>  
> -	if (slab->freelist) {
> +	if (READ_ONCE(slab->freelist)) {
>  		stat(s, DEACTIVATE_REMOTE_FREES);
>  		tail = DEACTIVATE_TO_TAIL;
>  	}
> -- 
> 2.39.3 (Apple Git-146)
> 
> 

Re: [PATCH] mm/slub: mark racy access on slab->freelist

[linke li]

> Thanks!  Do you have a data race report to copy+paste into the commit 
> description so people can search for it if they stumble across the same 
> thing?

I don't have a data race report, just try to analyze the code statically
and then check it manually. I hope I could help in some way.

Re: [PATCH] mm/slub: mark racy access on slab->freelist

[Vlastimil Babka]

On 4/27/24 10:51, linke li wrote:
> In deactivate_slab(), slab->freelist can be changed concurrently. Mark
> data race on slab->freelist as benign using READ_ONCE.
> 
> 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@qq.com>

Added to slab/for-6.10, thanks

> ---
>  mm/slub.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 0d700f6ca547..bb0e05a321e9 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2813,7 +2813,7 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab,
>  	struct slab new;
>  	struct slab old;
>  
> -	if (slab->freelist) {
> +	if (READ_ONCE(slab->freelist)) {
>  		stat(s, DEACTIVATE_REMOTE_FREES);
>  		tail = DEACTIVATE_TO_TAIL;
>  	}