Re: [PATCH] mm: memcg: fix NULL pointer in mem_cgroup_track_foreign_dirty()

[Kefeng Wang]

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@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > > 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.


[1] 
https://lore.kernel.org/all/20211020210755.23964-6-shy828301@xxxxxxxxx/T/#m1d40559ca2dcf94396df5369214288f69dec379b