linux-kernel - Re: [PATCH resend] mm: memcg: fix NULL pointer in mem_cgroup_track_foreign_dirty

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Message-ID: <27176f7a24fb37e5f011c7fa451bec7ba324e668.camel@gmail.com>
Date:   Sun, 29 Jan 2023 11:38:51 +0100
From:   mikoxyzzz@...il.com
To:     Kefeng Wang <wangkefeng.wang@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        Jan Kara <jack@...e.cz>, Shakeel Butt <shakeelb@...gle.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Ma Wupeng <mawupeng1@...wei.com>
Subject: Re: [PATCH resend] mm: memcg: fix NULL pointer in
 mem_cgroup_track_foreign_dirty_slowpath()

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.
> 
> Reported-by: Ma Wupeng <mawupeng1@...wei.com>
> Fixes: 97b27821b485 ("writeback, memcg: Implement foreign dirty
> flushing")
> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
> ---
> resend: correct function name
>  include/linux/memcontrol.h | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> 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,
>  static inline void mem_cgroup_track_foreign_dirty(struct folio
> *folio,
>                                                   struct
> bdi_writeback *wb)
>  {
> +       struct mem_cgroup *memcg;
> +
>         if (mem_cgroup_disabled())
>                 return;
>  
> -       if (unlikely(&folio_memcg(folio)->css != wb->memcg_css))
> +       memcg = folio_memcg(folio);
> +       if (unlikely(memcg && &memcg->css != wb->memcg_css))
>                 mem_cgroup_track_foreign_dirty_slowpath(folio, wb);
>  }
>  

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

--
~miko