CVE-2025-21861

Summary

CVE-2025-21861 is a vulnerability in the Linux kernel that affects the memory management subsystem. It was discovered that during the migration of memory control groups (memcg), if the migration failed, the destination folio's memcg_data was left unset. When trying to free such folios, the system would add them to the LRU list, causing memcg code to be unhappy. This issue could lead to unnecessary complaints from memcg and an unnecessary step of adding the folio to the LRU list. The new recommended flow is to simply remove the folio from the LRU after putting the last reference to it, avoiding this issue altogether.

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