From: Yang Shi <shy828301@gmail.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>,
Andrew Morton <akpm@linux-foundation.org>,
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>
Subject: Re: [PATCH] mm: memcg: fix NULL pointer in mem_cgroup_track_foreign_dirty()
Date: Wed, 1 Feb 2023 09:21:27 -0800 [thread overview]
Message-ID: <CAHbLzkqeU0eufPEw-dHJ6vGPWncHffa6NuxeihWOjWknDryD4g@mail.gmail.com> (raw)
In-Reply-To: <Y9odzlOwzCeErKKH@dhcp22.suse.cz>
On Wed, Feb 1, 2023 at 12:07 AM Michal Hocko <mhocko@suse.com> wrote:
>
> On Mon 30-01-23 11:30:47, Yang Shi wrote:
> > On Mon, Jan 30, 2023 at 4:20 AM Kefeng Wang <wangkefeng.wang@huawei.com> wrote:
> > >
> > >
> > >
> > > On 2023/1/30 16:48, Michal Hocko wrote:
> > > > On Mon 30-01-23 09:16:13, Kefeng Wang wrote:
> > > >>
> > > >>
> > > >> On 2023/1/30 5:48, Andrew Morton wrote:
> > > >>> On Sun, 29 Jan 2023 10:44:51 +0800 Kefeng Wang <wangkefeng.wang@huawei.com> wrote:
> > > >>>
> > > >>>> As commit 18365225f044 ("hwpoison, memcg: forcibly uncharge LRU pages"),
> > > >>>
> > > >>> Merged in 2017.
> > > >>>
> > > >>>> 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() to
> > > >>>> fix it.
> > > >>>>
> > > >>>> Reported-by: Ma Wupeng <mawupeng1@huawei.com>
> > > >>>> Fixes: 97b27821b485 ("writeback, memcg: Implement foreign dirty flushing")
> > > >>>
> > > >>> Merged in 2019.
> > > >>>
> > > ...
> > > >
> > > > Just to make sure I understand. The page has been hwpoisoned, uncharged
> > > > but stayed in the page cache so a next page fault on the address has blowned
> > > > up?
> > > >
> > > > Say we address the NULL memcg case. What is the resulting behavior?
> > > > Doesn't userspace access a poisoned page and get a silend memory
> > > > corruption?
> > >
> > > + Yang Shi
> > >
> > > Check previous link[1], seems that it is a known issue, and there is a
> > > TODO list for storage backed filesystems from Yang.
> >
> > For tmpfs and hugetlbfs, the page cache still stay in page cache, the
> > later page fault will handle the case gracefully. Other real storage
> > backed filesystem will have page cache truncated.
> >
> > The page cache will be uncharged before truncate. If the truncate
> > fails, we may end up in this case.
>
> This would be a good addendum to the changelog. What would be a typical
> failure in the truncation path?
For memory failure path, there may be a couple of cases, for example,
page is not for a regular file (maybe directory), fail to release
buffers, etc.
>
> > >
> > >
> > > [1]
> > > https://lore.kernel.org/all/20211020210755.23964-6-shy828301@gmail.com/T/#m1d40559ca2dcf94396df5369214288f69dec379b
>
> --
> Michal Hocko
> SUSE Labs
prev parent reply other threads:[~2023-02-01 17:21 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-29 2:44 [PATCH] mm: memcg: fix NULL pointer in mem_cgroup_track_foreign_dirty() Kefeng Wang
2023-01-29 4:09 ` [PATCH resend] mm: memcg: fix NULL pointer in mem_cgroup_track_foreign_dirty_slowpath() Kefeng Wang
2023-01-29 10:38 ` mikoxyzzz
2023-01-29 21:48 ` [PATCH] mm: memcg: fix NULL pointer in mem_cgroup_track_foreign_dirty() Andrew Morton
2023-01-30 1:16 ` Kefeng Wang
2023-01-30 8:48 ` Michal Hocko
2023-01-30 12:20 ` Kefeng Wang
2023-01-30 13:02 ` Michal Hocko
2023-01-30 19:30 ` Yang Shi
2023-02-01 8:07 ` Michal Hocko
2023-02-01 17:21 ` Yang Shi [this message]
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