mm: memcg: fix NULL pointer in mem_cgroup_track_foreign_dirty_slowpath()

As commit 18365225f044 ("hwpoison, memcg: forcibly uncharge LRU pages"),
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_dirty() to
fix it.

Link: https://lkml.kernel.org/r/20230129040945.180629-1-wangkefeng.wang@huawei.com
Fixes: 97b27821b485 ("writeback, memcg: Implement foreign dirty flushing")
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reported-by: Ma Wupeng <mawupeng1@huawei.com>
Tested-by: Miko Larsson <mikoxyzzz@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Ma Wupeng <mawupeng1@huawei.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index d3c8203..85dc9b8 100644 (file)
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1666,10 +1666,13 @@ void mem_cgroup_track_foreign_dirty_slowpath(struct folio *folio,
 static inline void mem_cgroup_track_foreign_dirty(struct folio *folio,
                                                  struct bdi_writeback *wb)
 {
+       struct mem_cgroup *memcg;
+
        if (mem_cgroup_disabled())
                return;
 
-       if (unlikely(&folio_memcg(folio)->css != wb->memcg_css))
+       memcg = folio_memcg(folio);
+       if (unlikely(memcg && &memcg->css != wb->memcg_css))
                mem_cgroup_track_foreign_dirty_slowpath(folio, wb);
 }