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


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

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