CVE-2026-46017mm: fix deferred split queue races during migration

Official description

In the Linux kernel, the following vulnerability has been resolved: mm: fix deferred split queue races during migration migrate_folio_move() records the deferred split queue state from src and replays it on dst. Replaying it after remove_migration_ptes(src, dst, 0) makes dst visible before it is requeued, so a concurrent rmap-removal path can mark dst partially mapped and trip the WARN in deferred_split_folio(). Move the requeue before remove_migration_ptes() so dst is back on the deferred split queue before it becomes visible again. Because migration still holds dst locked at that point, teach deferred_split_scan() to requeue a folio when folio_trylock() fails. Otherwise a fully mapped underused folio can be dequeued by the shrinker and silently lost from split_queue. [ziy@nvidia.com: move the comment]

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/cbf75cf212ee6e499abc1757fb4b5ae6d70ed0aa
• https://git.kernel.org/stable/c/3bac01168982ec3e3bf87efdc1807c7933590a85