UBUNTU-CVE-2026-89756: Low severity ubuntu/linux-aws vulnerability

In the Linux kernel, the following vulnerability has been resolved: mm/migrate: report RCU-tasks quiescent states in migratepagesbatch() migratepagesbatch() unmaps each folio before moving it, and every unmap runs the mmunotifier invalidate callbacks. On KVM hosts trytomigrate() ends up in kvmmmunotifierinvalidaterangestart() -> tdpmmuzapleafs(), which is expensive, so unmapping a large batch keeps the CPU busy for a long time. The loop already calls condresched(), but on PREEMPTION kernels that is a no-op, and involuntary preemption is not a Tasks-RCU quiescent state. A long batch therefore never reports a quiescent state, and the migrating task (e.g. kcompactd) becomes a Tasks-RCU holdout, stalling the Tasks-RCU grace period for minutes, which is common at Meta fleet: INFO: rcutasks detected stalls on tasks: 0000000055349ecc: .. nvcsw: 1157401/1157401 holdout: 1 idlecpu: -1/56 task:kcompactd0 state:R running task Call Trace: tdpmmuzapleafs tdpmmunextroot gfntopfncacheinvalidatestart kvmmmunotifierinvalidaterangestart mmunotifierinvalidaterangestart trytomigrateone trytomigrate migratepagesbatch migratepages compactzone compactnode kcompactd kthread Use condreschedtasksrcuqs() so a quiescent state is reported even when condresched() does nothing. This has also been discussed at [1]