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Date:   Thu, 26 Nov 2020 09:27:06 +1100
From:   Stephen Rothwell <sfr@canb.auug.org.au>
To:     Alex Shi <alex.shi@linux.alibaba.com>
Cc:     Lorenzo Stoakes <lstoakes@gmail.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Hui Su <sh_def@163.com>,
        Shakeel Butt <shakeelb@google.com>,
        Roman Gushchin <guro@fb.com>,
        syzbot <syzbot+ce635500093181f39c1c@syzkaller.appspotmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        Linux-Next Mailing List <linux-next@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm/memcg: warn on missing memcg on
 mem_cgroup_page_lruvec()
Message-ID: <20201126092706.1e06aa08@canb.auug.org.au>
In-Reply-To: <0918d6f5-8459-7b5e-82a3-6c9792d17433@linux.alibaba.com>
References: <00000000000054aea005b4d59e71@google.com>
        <20201125112202.387009-1-lstoakes@gmail.com>
        <0918d6f5-8459-7b5e-82a3-6c9792d17433@linux.alibaba.com>
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Hi all,

On Wed, 25 Nov 2020 20:15:11 +0800 Alex Shi <alex.shi@linux.alibaba.com> wr=
ote:
>
> Acked-by: Alex Shi <alex.shi@linux.alibaba.com>
>=20
>=20
> =E5=9C=A8 2020/11/25 =E4=B8=8B=E5=8D=887:22, Lorenzo Stoakes =E5=86=99=E9=
=81=93:
> > 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().
> >=20
> > 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 th=
is
> > is the case.
> >=20
> > Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
> > Reported-by: syzbot+ce635500093181f39c1c@syzkaller.appspotmail.com
> > ---
> >  include/linux/memcontrol.h | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >=20
> > 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(stru=
ct mem_cgroup *memcg,
> >  		goto out;
> >  	}
> > =20
> > -	VM_WARN_ON_ONCE(!memcg);
> >  	if (!memcg)
> >  		memcg =3D root_mem_cgroup;
> > =20
> > @@ -645,7 +644,10 @@ static inline struct lruvec *mem_cgroup_lruvec(str=
uct 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 =3D page_memcg(page);
> > +
> > +	VM_WARN_ON_ONCE_PAGE(!memcg, page);
> > +	return mem_cgroup_lruvec(memcg, pgdat);
> >  }
> > =20
> >  static inline bool lruvec_holds_page_lru_lock(struct page *page,
> >  =20

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/20201125112202.387009-1-lstoakes@gmail.com/
--=20
Cheers,
Stephen Rothwell

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