Message-ID: <27176f7a24fb37e5f011c7fa451bec7ba324e668.camel@gmail.com>
Subject: Re: [PATCH resend] mm: memcg: fix NULL pointer in
 mem_cgroup_track_foreign_dirty_slowpath()
From:   mikoxyzzz@gmail.com
To:     Kefeng Wang <wangkefeng.wang@huawei.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Tejun Heo <tj@kernel.org>, Jens Axboe <axboe@kernel.dk>,
        Jan Kara <jack@suse.cz>, Shakeel Butt <shakeelb@google.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Ma Wupeng <mawupeng1@huawei.com>
Date:   Sun, 29 Jan 2023 11:38:51 +0100
In-Reply-To: <20230129040945.180629-1-wangkefeng.wang@huawei.com>
References: <20230129024451.121590-1-wangkefeng.wang@huawei.com>
         <20230129040945.180629-1-wangkefeng.wang@huawei.com>
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On Sun, 2023-01-29 at 12:09 +0800, Kefeng Wang wrote:
> As commit 18365225f044 ("hwpoison, memcg: forcibly uncharge LRU
> pages"),
> hwpoison will forcibly uncharg a LRU hwpoisoned page, the folio_memcg
> could be NULl, then, mem_cgroup_track_foreign_dirty_slowpath() could
> occurs a NULL pointer dereference, let's do not record the foreign
> writebacks for folio memcg is null in
> mem_cgroup_track_foreign_dirty()
> to fix it.
>=20
> Reported-by: Ma Wupeng <mawupeng1@huawei.com>
> Fixes: 97b27821b485 ("writeback, memcg: Implement foreign dirty
> flushing")
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
> resend: correct function name
> =C2=A0include/linux/memcontrol.h | 5 ++++-
> =C2=A01 file changed, 4 insertions(+), 1 deletion(-)
>=20
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index eb6e5b18e1ad..35478695cabf 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -1688,10 +1688,13 @@ void
> mem_cgroup_track_foreign_dirty_slowpath(struct folio *folio,
> =C2=A0static inline void mem_cgroup_track_foreign_dirty(struct folio
> *folio,
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 st=
ruct
> bdi_writeback *wb)
> =C2=A0{
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0struct mem_cgroup *memcg;
> +
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (mem_cgroup_disabled()=
)
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0return;
> =C2=A0
> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (unlikely(&folio_memcg(foli=
o)->css !=3D wb->memcg_css))
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0memcg =3D folio_memcg(folio);
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (unlikely(memcg && &memcg->=
css !=3D wb->memcg_css))
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0mem_cgroup_track_foreign_dirty_slowpath(folio, wb);
> =C2=A0}
> =C2=A0

Might want to Cc linux-stable.
Tested-by: Miko Larsson <mikoxyzzz@gmail.com>

--
~miko