linux-kernel - Re: [External] Re: [PATCH] mm/memcg: fix NULL pointer dereference at workingset

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Message-ID: <20201130134514.GL17338@dhcp22.suse.cz>
Date:   Mon, 30 Nov 2020 14:45:14 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Roman Gushchin <guro@...com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        alex.shi@...ux.alibaba.com, alexander.h.duyck@...ux.intel.com,
        Yafang Shao <laoar.shao@...il.com>, richard.weiyang@...il.com,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [External] Re: [PATCH] mm/memcg: fix NULL pointer dereference at
 workingset_eviction

On Mon 30-11-20 21:36:49, Muchun Song wrote:
> On Mon, Nov 30, 2020 at 9:23 PM Michal Hocko <mhocko@...e.com> wrote:
> >
> > On Mon 30-11-20 21:15:12, Muchun Song wrote:
> > > We found a case of kernel panic. The stack trace is as follows
> > > (omit some irrelevant information):
> > >
> > >     BUG: kernel NULL pointer dereference, address: 00000000000000c8
> > >     RIP: 0010:workingset_eviction+0x26b/0x450
> > >     Call Trace:
> > >      __remove_mapping+0x224/0x2b0
> > >      shrink_page_list+0x8c2/0x14e0
> > >      shrink_inactive_list+0x1bf/0x3f0
> > >      ? do_raw_spin_unlock+0x49/0xc0
> > >      ? _raw_spin_unlock+0xa/0x20
> > >      shrink_lruvec+0x401/0x640
> > >
> > > This was caused by commit 76761ffa9ea1 ("mm/memcg: bail out early when
> > > !memcg in mem_cgroup_lruvec"). When the parameter of memcg is NULL, we
> > > should not use the &pgdat->__lruvec. So this just reverts commit
> > > 76761ffa9ea1 to fix it.
> > >
> > > Fixes: 76761ffa9ea1 ("mm/memcg: bail out early when !memcg in mem_cgroup_lruvec")
> >
> > I do not see any commits like that in the current Linus tree. Is this a
> > commit id from the linux-next? If yes, can we just fold it into the
> > respective patch in mmotm tree please?
> 
> Yes. This commit is on the linux-next tree.

FYI, patches coming from mmotm are constantly rebased in linux-next so
the sha1 is meaningless and shouldn't be added as a reference in the
changelog.

> Of course can.

Thanks! I believe Andrew should be able to just pick up the patch and
make it -fix patch.

-- 
Michal Hocko
SUSE Labs