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Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH] mm: memcg: fix NULL pointer in mem_cgroup_track_foreign_dirty() Content-Language: en-US To: Michal Hocko CC: Andrew Morton , Tejun Heo , Jens Axboe , Jan Kara , Shakeel Butt , Naoya Horiguchi , , , Ma Wupeng , References: <20230129024451.121590-1-wangkefeng.wang@huawei.com> <20230129134815.21083b65ef3ae4c3e7fae8eb@linux-foundation.org> <568c10e8-c225-b3c4-483a-5bb3329de4c5@huawei.com> From: Kefeng Wang In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpemm500001.china.huawei.com (7.185.36.107) X-CFilter-Loop: Reflected X-Rspamd-Queue-Id: 95949180008 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: x9jq1z6czu87cpr8ykxihjfkfew1cnu5 X-HE-Tag: 1675081221-692135 X-HE-Meta: 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 YbM5U0jp YeDudMzh9LUkone1VXVM/OkD7nwLYxxuqf/8iVbjNGI+sND9Wg7Gjue2lfWt6+JrWdr3x9u4vUkkWrmnpboOcA9ubwgNt2R2SiugtjbnT1usnPcNN437pVkxInigxZ29UCSoK3U/QP2ZZ9nFK+rXFFFJokzIqFOFSKuaiH2YhXJsGBo0tXYuErQEWV/ZL5myAsBg+nbh8fiTCDaxHdtIq983fbcZ5+b10zG3SWb2kw8RQ/KhKEmjl1WidgKViNU7tFZ6rqIJjyozrjizRvbCCMGZhqk5po4frqF1liT+sixnycqTYb3FmRceVRN0NU16cux8hV/ySehY097bVF5IIC7EX57Hg5KSLNrbq X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 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 >>>> 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