Subject: Re: [PATCH] mm/memcg: warn on missing memcg on mem_cgroup_page_lruvec()

From: Stephen Rothwell <[email-masked]>
Date: Thu, 26 Nov 2020 09:27:06 +1100

Hi all,

On Wed, 25 Nov 2020 20:15:11 +0800 Alex Shi <[email-masked]> wrote:
>
> Acked-by: Alex Shi <[email-masked]>
> 
> 
> 在 2020/11/25 下午7:22, Lorenzo Stoakes 写道:
> > Move memcg check to mem_cgroup_page_lruvec() as there are callers which
> > may invoke this with !memcg in mem_cgroup_lruvec(), whereas they should
> > not in mem_cgroup_page_lruvec().
> > 
> > We expect that we have always charged a page to the memcg before
> > mem_cgroup_page_lruvec() is invoked, so add a warning to assert that this
> > is the case.
> > 
> > Signed-off-by: Lorenzo Stoakes <[email-masked]>
> > Reported-by: [email-masked]
> > ---
> >  include/linux/memcontrol.h | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > index 87ed56dc75f9..3e6a1df3bdb9 100644
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -618,7 +618,6 @@ static inline struct lruvec *mem_cgroup_lruvec(struct mem_cgroup *memcg,
> >  		goto out;
> >  	}
> >  
> > -	VM_WARN_ON_ONCE(!memcg);
> >  	if (!memcg)
> >  		memcg = root_mem_cgroup;
> >  
> > @@ -645,7 +644,10 @@ static inline struct lruvec *mem_cgroup_lruvec(struct mem_cgroup *memcg,
> >  static inline struct lruvec *mem_cgroup_page_lruvec(struct page *page,
> >  						struct pglist_data *pgdat)
> >  {
> > -	return mem_cgroup_lruvec(page_memcg(page), pgdat);
> > +	struct mem_cgroup *memcg = page_memcg(page);
> > +
> > +	VM_WARN_ON_ONCE_PAGE(!memcg, page);
> > +	return mem_cgroup_lruvec(memcg, pgdat);
> >  }
> >  
> >  static inline bool lruvec_holds_page_lru_lock(struct page *page,
> >   

I have added that patch to the akpm tree in linux-next today as a fix
for "mm/memcg: add missed warning in mem_cgroup_lruvec".

Andrew: the original patch is here:
https://lore.kernel.org/lkml/[email-masked]/
-- 
Cheers,
Stephen Rothwell