On 2021/4/1 11:35, Roman Gushchin wrote: > On Thu, Apr 01, 2021 at 11:31:16AM +0800, Miaohe Lin wrote: >> On 2021/4/1 11:01, Muchun Song wrote: >>> Christian Borntraeger reported a warning about "percpu ref >>> (obj_cgroup_release) <= 0 (-1) after switching to atomic". >>> Because we forgot to obtain the reference to the objcg and >>> wrongly obtain the reference of memcg. >>> >>> Reported-by: Christian Borntraeger <[email protected]> >>> Signed-off-by: Muchun Song <[email protected]> >> >> Thanks for the patch. >> Is a Fixes tag needed? > > No, as the original patch hasn't been merged into the Linus's tree yet. > So the fix can be simply squashed. > > Btw, the fix looks good to me. > > Acked-by: Roman Gushchin <[email protected]> >
I see. Many thanks for explanation! The code looks good to me. Reviewed-by: Miaohe Lin <[email protected]> >> >>> --- >>> include/linux/memcontrol.h | 6 ++++++ >>> mm/memcontrol.c | 6 +++++- >>> 2 files changed, 11 insertions(+), 1 deletion(-) >>> >>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h >>> index 0e8907957227..c960fd49c3e8 100644 >>> --- a/include/linux/memcontrol.h >>> +++ b/include/linux/memcontrol.h >>> @@ -804,6 +804,12 @@ static inline void obj_cgroup_get(struct obj_cgroup >>> *objcg) >>> percpu_ref_get(&objcg->refcnt); >>> } >>> >>> +static inline void obj_cgroup_get_many(struct obj_cgroup *objcg, >>> + unsigned long nr) >>> +{ >>> + percpu_ref_get_many(&objcg->refcnt, nr); >>> +} >>> + >>> static inline void obj_cgroup_put(struct obj_cgroup *objcg) >>> { >>> percpu_ref_put(&objcg->refcnt); >>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >>> index c0b83a396299..64ada9e650a5 100644 >>> --- a/mm/memcontrol.c >>> +++ b/mm/memcontrol.c >>> @@ -3133,7 +3133,11 @@ void split_page_memcg(struct page *head, unsigned >>> int nr) >>> >>> for (i = 1; i < nr; i++) >>> head[i].memcg_data = head->memcg_data; >>> - css_get_many(&memcg->css, nr - 1); >>> + >>> + if (PageMemcgKmem(head)) >>> + obj_cgroup_get_many(__page_objcg(head), nr - 1); >>> + else >>> + css_get_many(&memcg->css, nr - 1); >>> } >>> >>> #ifdef CONFIG_MEMCG_SWAP >>> >> > . >
