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

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Date:   Mon, 30 Nov 2020 12:23:57 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Michal Hocko <mhocko@...e.com>,
        Muchun Song <songmuchun@...edance.com>,
        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>,
        Dmitry Osipenko <digetx@...il.com>
Subject: Re: [External] Re: [PATCH] mm/memcg: fix NULL pointer dereference
 at workingset_eviction

On Mon, 30 Nov 2020 16:57:37 +0100 Vlastimil Babka <vbabka@...e.cz> wrote:

> On 11/30/20 2:45 PM, Michal Hocko wrote:
> > 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.
> 
> Well the fix is a revert, so just remove the patch from mmotm/next?
> BTW, looks like it wasn't sent to linux-mm [1], looks like missing To: header.
> 
> [1] 
> https://lore.kernel.org/lkml/1606446515-36069-1-git-send-email-alex.shi@linux.alibaba.com/

Yes, I've dropped "mm/memcg: bail out early when !memcg in
mem_cgroup_lruvec", thanks.