On 2024/3/9 15:48, linke li wrote:
> 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@xxxxxx>
> ---
> 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);
There is another unmarked access of "slab->slabs" in the show_slab_objects(),
which you can change too.
I'm not sure that it's really safe to access "slab->slabs" here without any protection?
Although it should be no problem in practice, alternative choice maybe putting partial
slabs count in the kmem_cache_cpu struct.
Thanks.
